Technical Faqs

01 General Building

Can Acraseal be used to seal sandstone and composite concrete tiles

22nd February 2011
Acraseal can be used to seal any porous stone or cement based tiles. We would always recommend trialling in a small inconspicuous area first to ensure compatability and that the deisred finish is attained. Once applied to a surface, Acraseal is very difficult to remove.
Can you advise, after using Larsen Concentrated Algicide if the surface can be painted?

10th September 2008
After the Larsen Concentrated Algicide has been applied and has dried, the surface can then have subsequent coatings applied, i.e. paint, plaster, render etc. It is important to ensure the surface is sound, clean and free from other contamination before applying subsequent coatings.
Could i have sone information relating to health and safety for the use of mortar plastiser.

2nd June 2009
The Health and Safety information is provided in the safety datasheet on the product page - Mortar Plasticiser
Couldyou recommend a waterproofing product suitable to use on an existing terrazzo floor for a new vinyl to be laid on.

16th February 2010
By waterproofing product I would assume you mean a damp proof membrane.
If the moisture content of the existing terrazzo floor is too high to apply the vinyl directly, then Larsen DPM can be applied to the terrazzo. The floor should be mechanically prepared (e.g. enclosed shot blasting) to give a clean, lightly textured finsih free from contamination. Then apply Larsen DPM in two coats (constrasting colours are available for refernence).
Depending on the adhesive used to stick the vinyl, a minimum of 3mm of levelling compound may be required (consult adhesive manufacturer for advice). If this is the case the wet second coat of DPM should be fully broadcast with a dry single size sand e.g 16/30 at a rate of 2kg per sq. m. when cured, excess sand should be removed to provide an adequate mechanical key for the levelling compound.
Do you have a product that can be added to a plaster mix to help prevent cracks in smooth "rubbed up" render finish?

22nd November 2008
Generally, cracking in plaster is the result of shrinkage and there a few main causes and methods to reduce incidence of cracking.
Cause: Shrinkage in blockwork. All masonry substrates are prone to shrinkage as they dry out if plastering is applied beofre the structure has 'settled' there is a greater risk of cracks developing at the corners of windows and doorways.
Solution: Allow blockwork to dry out sufficieintly before plastering. Include suitable reinforcing (scrim cloth etc) at critical areas.
Cause: Render is too strong.
Solution: As a general rule of thumb, work on the principle hard centre, soft shell. As you work out from the wall subsequent coats should get weaker to reduce the risk of cracking. The stronger the mix the greater the risk of cracking.
Cause: Normal drying shrinkage. Sunny or windy conditions especially can cause the render to dry out too quickly resulting in crazing of the surface.
Solution: Try to work in the best weather conditions and allow adequate curing by covering with polythene etc or misting with water over the first 7 days.
Additional measures can be taken to reduce the incidence of cracks in render e.g. by adding polypropylene fibres to mix or a polymer additive. However, the best solution is to employ the best working practice where possible.
Do you have any epoxy resin with shear strength more than 20MPa?thanks

7th July 2009
Larsen Epoxy Bond has a slant/shear strength of >30MPa.
How do I clean cement off brick (DARK RED) coloured pavers.

20th May 2009
Remove as much of the cement or mortar residue as possible by mechanical means (scraping or brushing). Wet the area fully, then apply Brick and Patio Cleaner as directed.
As Brick and Patio Cleaner is an acid based cleaner great care should be taken in its application, also it is worth noting that it will attack all cement based materials so an inconspicuous trial area should always carried out first.
i have a white slapdashed
wall about 12 years old and a red colour has appeared. is there anything made to clean it?

7th March 2011
The red colour is probably as the result of an algae growth. Larsen Concetrated Algicide will be suitable to treat and clean the wall. The following is the product datasheet.
I have concrete pavers which have previously been improperly sealed, leaving the dark pavers streaked and milky in color. What can I use to strip down these pavers to remove the old sealent and to restore them to their natural color?

23rd February 2010
This is dependent on the nature of sealer used, however a proprietary paint stripper would be worth trying.
I have put sandstone on part of my house, however it seems to be letting water in. Do ye have a suitable sealer to stop this.

4th November 2009
Larsen Water Repel can be applied to most absorbent surfaces such brick, render or in this case sandstone and will provide a water repellent seal against driving rain.
Water Repel must be applied to a dry surface in dry conditions.
An alternative is Larpruf SWR which is a water based silicone type water repellent.
i need a adhesive fo fix some brick slips to the exterior of my house, i beleve i used some larsen quick dry floor tile adhesive a few months ago and on the packet am sure it said i could use it for brick slips,if i am wrong what can you recomend thanks

19th February 2010
Our cement based tile adhesives are suitable for use externally and would be ideal for fixing brick slips. It is probably better to use a Flexible (S1) standard setting product e.g. Larsen Professional Flexible Standard Set. This will give a long working time and allow adjustment of the brick slips.
I need to bond stainless steel plate 180sq (3mm thick) to concrete (precast unit). Which product do you recommend?

29th April 2008
We have a number of bonding agents which would be suitable. For light duty, non-structural bonding, then I would recommend Fast Grab Construction Adhesive or Bond & Seal. For heavy duty, structural bonding, I would recommend Larfix E.
I need to know the rate at which I should dilute Acraseal. Have you got a system to dilute and what equiptment is advised to spray this product on. Should I put Algicide or Acraseal on first on concrete tiles and slate?

30th June 2008
Acraseal is supplied ready for use and should not be further diluted.
Acraseal should be applied by roller, brush or suitable sprayer e.g. Larsen Galvanised Spray Unit. When spraying care should be taken to avoid the overspray contaminating surrounding areas as the selaer will be very difficult to remove. Acraseal is solvent based - ensure adequate ventilation exists and read safety datasheet before use.
Where there is a build up of algae etc, apply Larsen Concentrated Algicide before sealing. Allow treated area to fully dry before applying any sealer. Where there is a very heavy build up of dirt, moss etc. it is often advisable to clean with a powerhose, then apply Algicide, allow to fully dry then seal as required.
I wanted to ask if Larfix E could be used to bond galvanised lateral restraint straps to precast units/blockwork rather than using bolts/anchors? The lateral restraints were not placed at the time of building and I am trying to fit them remedially, but do not want to use bolts/anchors.

23rd September 2011
Larfix E will bond the straps very stongly to the surface of concrete or blockwork, however I would recommend running it past an engineer for advice.
Depending on what you are bonding to, will have an influence as you will be relying on the surface strength of the substrate to carry the load (pull-off or shear) rather than an anchor (pull-out).
Is it ok to use Bitumen Paint internally on brickwork (intend covering with plaster when paint dry)

10th January 2011
The use of Black Bitumen Paint in this application will provide a surface which would be very difficult to apply plaster to.
A better product to use would be Larsen Rubberproof which is a water based, rubberised, bitumen emulsion. This should be applied in two coats with the top coat fully broadcast with a clean dry 0.6-1.2mm sand to provide a key for the plaster.
Is Larsen brick and patio cleaner harmful to plants?

16th June 2008
Larsen Brick and Patio Cleaner is a Hydrochloric Acid based cleaning product. While it is not classified as 'Corrosive' it would be expected to damage acid sensitive surfaces and this could include plants. It is also possible that spillages on soil would upset the pH of the soil temporarily in the localised area and this too could be damaging to plants.
seeking advice on how to prevent cracking in a narrow band of external render applied to metal lath fixed to timber beam, dimensions 0.3m deep by 3.5m long? i'm thinking expansion joints, glass fibre mesh and polymer additive.

20th October 2010
Your idea is correct, add Larcem 25 SBRBond to the render mix (dilute 3:1 with clean water and use this as the gauging liquid). The inclusion of reinforcing mesh and a separation joint will further reduce the risk of cracking.

02 Concrete

Concrete has popped in back yard can you advise me on what material there is available to lay a screed over the top and what material i would need to use to bond this to the exixiting concrete. many thanks

17th April 2011
It is important to adequately prepare the surface by water jetting or other mechanical means to ensure a solid substrate free of all loose or weak material. Once this is achieved, Larsen Professional SLC2050 External self-levelling compound can be applied to the surface without the need for primer.
Hi there,- in the tech datasheet for larcem 25 SBR it is recomended that chemcrete 100+ be used as a super plasticiser when producing microconcrete. would there be any problem using chemecrete HP3 super plasticiser in its place?

12th January 2012
Chemcrete HP3 superpalsticiser is also suitable. Make sure the superplasticiser and the SBR are added separately to the mix.
I am installing a 1700sq/ft freezer room that operates at a temperature of -25 oc (minus 25). I employed a contractor to power float the floor to give it a sealed finish, however the floor hardened too quickly. Apart from taking out the floor again (150mm fibre mesh, 40 newton concrete) is there a product available that will seal the floor, operate within a temp. of -25 and will withstand the combined weight of a forklift and pallet travelling on the floor on a regular basis. (combined weight is 2,500kg)??

17th March 2008
Larsen Impregnation is a high quality, 2-pack epoxy sealer for concrete. It is ideal for use in industrial situations to seal and protect the floor. Impregnation will be suitable for a service temperarure -30 to +60^oC.
I am renovating an old red brick house that has some structural cracks. What grout do I use to repair the cracks with?
Also an old I beam is rusting. What product can I apply to retard the rust?
Thanks

29th April 2009
Structural cracks in a house should be fully investigated by a professional surveyor prior to carrying out any repairs. Depending on the cause, nature and size of cracks there a number of options as to which product/method to employ. At the simplest, the repair required may be only aesthetic and the most severe the wall may require 'stitching' or the wall needing underpinned. Until this is known a product cannot be recommended.
Depending on the location of the I beam the simplest option may be to blast or wire brush back to bare metal and then painting the beam with something like Black Bitumen Paint.
I have a wood block wooden floor in the kitchen which is lifting away from the concrete underneath due to damp. I want to remove this wooden floor and then apply Larcote DPM to seal the floor. Can a self leveling screed then be used on the resin so that a lino floor covering can be laid? If so which products would you recommend?

27th October 2011
Yes. The best method is to apply the DPM in two coats. The second coat is then fully broadcast while still wet with 0.6-1.2mm dry sand to excess (apporx. 2kg per sq. m.) This is then allowed to harden and the excess sand removed by brush or vacuum to leave a sandpaper-like finish which provides a mechanical key for subsequent coatings, i.e. levelling compounds.
The levelling compound to use depends on the thickness to be made up - up to 6mm use Larsen Latex Levelling compound; up to 25mm use Larsen SLC1500.
I have an issue within a church building. The issue is with the windows. the mullions are concrete and go from outside to in with no cavity. this is causing dampness on the inside walls. I am trying to find some sort of insulation to apply to the wall which can be allowed to have plaster then applied on top of it. At the very least we need an appropriate paint.

4th November 2011
There are two issues to be dealt with separately in this case. Firstly the prevention of damp soaking through the mullion - this can be prevented by applying a suitable water repellent impregnation treatment. I would recommend our product REPEL C for this application, which is a creamy silane water repellent which when applied to the external face of the mullion will leave it with a very low water absorption.
Secondly, the cold bridge created by the mullion can be treated with careful detailing of a suitable insulation material and probably plasterboard to the internal face of the mullion.
I would not recommend just applying a paint or insulation to the inside as the damp will still be travelling through the concrete and will likely surface elsewhere as a different problem. The application of REPEL C should stop the ingress of moisture through the concrete.
I have concrete imprint on my driveway.The paint has lifted/flaked in areas and
I want to re paint it.The colour is black.Where in Ashbourne,Co.Meath ,Ireland are the stockists of Larsen's paint/sealer?

12th July 2010
Normally, printed concrete driveways are not painted, rather the concrete is coloured and then the surface is sealed with a product such as Larseal Super or Larsen Acraseal. We do not sell coloured paints or coloured sealers for this application. For details of where Larseal Super or Acraseal can be purchased contact our Dublin Office on 018348255
I recently applied Acraseal to a newly poured concrete driveway (5 days old). I did this based on the contractor's recommendations. Should I have any concerns regarding the concrete curing properly, sealer working etc.

20th October 2010
Acraseal can function as both a sealer and a curing membrane for fresh concrete. Ususally when used as a curing membrane it is applied as soon as the concrete can be walked on. There should be no problems with your application, however in order to achieve a good seal you may want to apply a second coat of Acraseal.
Is there any compatibility issues in using HP3 super plasticiser along with your SRA or the SC1? Is there there any compatibility issues with using all three together?

22nd August 2011
There should be no issue using these products together in a mix. While there shouldn't be any issue, it would be advisable to dose separately to the mix. Always carry out trial mixes before use.
We are looking for a product to seal a painted concrete surface which would then allow us to lay ceramic tiles.

23rd January 2011
When tiling onto painted surrfaces it is very important to ensure the quality and bond of the paint is sufficient to support the tiling installation. Good quality gloss or epoxy paints may provide a suitable base for tiling, but cheaper floor paints and emulsion should generally be mechanically removed before tiling.
If the paint is sound, I would recommend using Larprime EU. This is a two pack solvent free epoxy primer. After mixing apply to the floor with a roller and then while still wet apply a broadcast sand scatter of dry 16/30 sand at a rate of 2kg per sq. m. Leave overnight for the primer to harden and then brush or vacuum to remove excess sand. This will leave a sandpaper like finish to provide a mechanical key for tiling.
We are looking for product that will allow render to be applied to fair face concrete precast panels. Can you assist.

15th January 2009
Larcem 55 is a styrene acrylic copoloymer emulsion bonding agent which is ideal for use in just such an application.
Ensure the wall is clean and free from mould oil residue (power washing may be required) or other contamination. Mix Larcem 55 neat with cement until a slurry consistency is reached (normally about 3:1). This is then applied to the wall and either:
1. Apply render wet on wet to the Larcem 55 slurry (within about 20min of appliying slurry).
2. Apply slurry to wall and finish with a brush or textured roller to a stippled finish and allow to harden before rendering (this will provide a mechanical key).
We concreted our back yard about 2 years ago this spring/summer. Recently the concrete has started to pop up in places, probably due to rainwater trapped, forming molecules, and now with the heavy frost these have started to open up all over the yard area. Is there anything that can be applied to combat this problem. I would be grateful for your advices. Many thanks

6th February 2009
You are probably correct in your assumption. The action of water trapped in the concrete surface freezing causes an increase of the volume of the water as it turns to ice and this can cuase pop outs. There are also other causes for example the presence of pyrites in the aggregate.
The best way to prevent the pop outs resulting from frost damage is to include an air entrainment admixture (e.g. Chemcrete E110) in the concrete when it is mixed. This creates a controlled air void which provides space for the ice to expand into without causing damage.
As this concrete is in place the only option would be to seal the surface with a suitable product to prevent moisture soaking into the top layer of the concrete and hence reduce the risk of pore ice formation. However, as this is external concrete and therefore unlikely to have a damp course beneath, there is still the risk of ground moisture migrating up through the concrete and in turn this could freeze during a a bad frost.
What product do I seal concrete with to allow me to tile after 3 days curing

7th April 2010
Current recommendations and best practice suggest concrete should be 6 weeks old before tiling. This allows the concrete to have gained a suitable level of strength and dryness and ensures that the majority of any early age shrinkage and associated cracking has taken place before tiling.
The main risk from tiling too early is that drying shrinkage cracking may occur in the concrete leading to cracking or debonding in the tiling installation.
If you are forced to tile onto concrete this early we would recommend using a decoupling matting system, such as our Seri-Dec. These systems help prevent stresses from the substrate being transmitted into the floor finish.
For further information consult our new tiling brochure or phone for further technical advice.
When applying a second coat of larsen concrete dustproofer to concrete floor, how long do you leave the first coat before applying the second?

21st April 2009
The second coat can be applied as soon as the first has absorbed into the concrete.
After the application of the final coat has been applied, it is important to ensure there are no puddles of Dustproofer remaining on the surafce. Before teh final application has dried, the floor should be well rinsed with clean water.

03 Flooring

can any of your self levelling products be used externally ie to level the floor of a large dog pen?

21st December 2009
Unfortunately we do not have an external grade self-levelling compound at this stage.
Could you please recommend a product for raising a screed floor by 8-10mm. The screed has Underfloor heating and will be tiled.

13th June 2008
Larsen Professional SLC 1500 would be the best product to use. This is a single pack (water mix) self-levelling compound for application from 0-25mm depth. It is suitable for use over underfloor heating.
For further information and datasheet, follow this link - SLC 1500
Couldyou recommend a waterproofing product suitable to use on an existing terrazzo floor for a new vinyl to be laid on.

16th February 2010
By waterproofing product I would assume you mean a damp proof membrane.
If the moisture content of the existing terrazzo floor is too high to apply the vinyl directly, then Larsen DPM can be applied to the terrazzo. The floor should be mechanically prepared (e.g. enclosed shot blasting) to give a clean, lightly textured finsih free from contamination. Then apply Larsen DPM in two coats (constrasting colours are available for refernence).
Depending on the adhesive used to stick the vinyl, a minimum of 3mm of levelling compound may be required (consult adhesive manufacturer for advice). If this is the case the wet second coat of DPM should be fully broadcast with a dry single size sand e.g 16/30 at a rate of 2kg per sq. m. when cured, excess sand should be removed to provide an adequate mechanical key for the levelling compound.
do we need to use a special latex screed on top of a floor treated with the speedo accelerator

29th September 2009
No. Once hardened, Speedo screed can be treated as any other, so any common levelling compound may be used.
Do you do a non- cementitious latex levelling compound?

3rd June 2011
No not currently. However if your application is to level a gypsum based screed, then a standard latex levelling compound could be used providing the screed is first sealed with two coats of suitable primer.
Do you have a product to seal granite paving?

5th July 2010
We have a number of products which are suitable for sealing ganite paving, depending on the finish required. If you are happy for the appearance of the paving to remain relatively unchanged , iwould recommend the application of Larsen Streetscape Protector applied in two coats.
Garage Floor repair:
the top surface of the garage floor is breaking down and generally the floor is very dusty. What products should we use to repair and seal the floor?

10th September 2009
Remove as much loose material as possible and then treat the floor with either Larsen Injection Resin or Larsen Impregnation - both are low viscosity epoxy products which should penetrate the concrete and help to bind up and strengthen any loose or weak material
Hi, I am interested in your stain resistant flexible grout. I am about to lay mosaic floor tiles, each tile is 100mmx50mm and they are set in a brick pattern on web backing on a 300mm x 300mm sheet. As they are a rustic design, the gaps between the tiles varies from around 2mm and 7mm, with 4-5mm being the average. Hence do I use the narrow joint or wide joint grout? Will the wide joint grout be able to cope with the small gaps or will the narrow joint grout be able to cope with the wider ones?

30th March 2010
Our Stain Resistant Wide Joint Grout would be the most suitable for this application as it is suitable for use in joints of 2 -20mm. Regading colour samples etc if you call our Sales Manager Martin Colbey (07710864636), he should be able to locate your nearest stockist.
i have a customer whos tiles have lifted off the floor. after inspecting the floor it seems that she has put a layer of varnish on the finished floor to keep dust down which proably lead to the tiles lifting. she now wants to retile the floor. is there anything i can put over the varnish or would i be better to remove the varnish. would flexibilzing the floor and throuwing sand on it letting it set and brushing off the excess ans then laytexing the floor be ok before tileing it again or not. please advise

12th March 2010
The best method would be to mechanically prepare the floor e.g. grinding back to a good quality absorbent substrate. It is worth noting that the floor may be of poor quality if it was initially 'varnished' to keep the dust down. An alternative option would be to use a decoupling membrane such Larsen Ser-Dec and leave the'varnish' in-situ.
I have a wood block wooden floor in the kitchen which is lifting away from the concrete underneath due to damp. I want to remove this wooden floor and then apply Larcote DPM to seal the floor. Can a self leveling screed then be used on the resin so that a lino floor covering can be laid? If so which products would you recommend?

27th October 2011
Yes. The best method is to apply the DPM in two coats. The second coat is then fully broadcast while still wet with 0.6-1.2mm dry sand to excess (apporx. 2kg per sq. m.) This is then allowed to harden and the excess sand removed by brush or vacuum to leave a sandpaper-like finish which provides a mechanical key for subsequent coatings, i.e. levelling compounds.
The levelling compound to use depends on the thickness to be made up - up to 6mm use Larsen Latex Levelling compound; up to 25mm use Larsen SLC1500.
I have an old stone cottage with an old suspended wood floor in one room. I want to reduce the draft by putting vinyl down over the wood. I was advised to roll a layer of bitumen first to seal the floor as much possible. Is this safe/effective in terms of moisture collecting under the vinyl? Are there any problems (or other alternatives) I should consider?

19th July 2011
Ideally the best solution would be to access the under side of the floor and install suitable insulation - there are various metods by which this can be achieved.
Draughts can be greatly reduced by sealing joints between floorboards (larger joints with timber slivers or cork) and below skirting with Multipurose silicone or Painter's Caulk.
The most important thing to ensure when either sealing, covering or installing is that the timbers remain sufficiently ventilated to prevent moisture build-up and ensuing rot.
I have had to take up an Amtico floor as it failed after 2 months. It was layed on top of ceramic tiles. The installers did not initially damp test the floor before putting it down. The ceramic tiles have now been removed and we have tried to remove the ceramic tile adhesive underneath but some of it won't budge. Using a kango machine is doing too much damage to the floor scredd underneath. The floor is now quite uneven and bumpy. On top of that there seems to be a problem with the damp proof membrane under the floor slab and we have high moisture readings and this is what contributed to the floor failing initially. How can the floor be damp proofed now, how can it be levelled and prepared for a new flooring and what is the best flooring solution in your opinion? Can Amtico be laid on it again? Do I have to go back to ceramic tiles? It is a kitchen.

16th July 2010
A surface applied damp proof membrane can then be applied to the floor to deal with the damp problem - Larsen DPM. It is best to apply DPM to a flat surface therefore the residue of adhesive can either be removed with the use of a floor grinder (rather than a Kango) or, as long as the majority of adhesive has been removed from the floor and any remaining adhesive is firmly bonded, a leveling compound can be laid over the floor. If this <6mm, I would recommend the use of our Latex Leveling compound.
Depending on which adhesive is being used to bond the Amtico, a second application of leveling compound (min 3mm) maybe required over the DPM to provide an adsorbent base for the glue.
i need a adhesive fo fix some brick slips to the exterior of my house, i beleve i used some larsen quick dry floor tile adhesive a few months ago and on the packet am sure it said i could use it for brick slips,if i am wrong what can you recomend thanks

19th February 2010
Our cement based tile adhesives are suitable for use externally and would be ideal for fixing brick slips. It is probably better to use a Flexible (S1) standard setting product e.g. Larsen Professional Flexible Standard Set. This will give a long working time and allow adjustment of the brick slips.
I need to raise a floor 10mm before putting down ceramic/stone type tiles. The floor surface is concrete screed. The area will be 10 meters square approx and will only be the product you suggest (no underfloor heating). I am concerned about it not cracking as its 10mm thick and if possible something that will dry in a day as its in my hallway and I will have no access once it is laid. The only other consideration is cost as its a large area.
Thank you for your help.

23rd September 2010
Larsen Professional SLC1500 is a self-levelling compound for use up to 25mm and it would be suitable for this application. For 10m x 10mm you would require approx 8 bags.
I need to screed an existing garage concrete floor to level (2-3mm) & apply decorative finish(can be resin based but needs to be coloured). Can you recommend a product?

25th August 2009
While a standard levelling compound may be suitable, I would recommend the use of Larsen Professional SLC 1500 as the levelling compound. This high quality leveling screed can be applied from next to nothing up to 25mm and will provide a very good finish for the application of decorative finishes.
In terms of finish we have two suitable products -
Polyfloor - a medium duty single pack floor paint
WDC - a two pack epoxy coating offering superior wear resistance
Both are avaialbel in red, light grey and dark grey as standard.
I'm carrying out remedial works to a suspended timber floor (steel joists, 18mm ply, + 6mm ply cross boarded glued and screwed). I need to spot fill the screws heads and, fill the joints in the plywood with a suitable filler. All in middle of live A&E dept - so smell, fumes are an issue. Can you recommend a product? Regards,
Dennis Brownlee
07764313244
(Belfast)

4th October 2010
We have a cement based filler which only needs mixed with water - Feather Edge. This is a fast setting, fine filler ideal for your application.
For prices and further information contact Andrew Duffy a.duffy@larsenbuildingproducts.com
I've been suppled with Larsen Flexible Floor Tile Adhesive by a tile supplier. Screed has gone down today. The screeder advised we'd need a specialised adhesive if we wanted to tile quickly, otherwise we'd have to wait 1 day /mm of screed until it was fully set, especially as we have underfloor heating installed. at 100mm od screed, we'd have over 3 months to wait. Is the adhesive supplied by the tile company suitible? If not, do you supply an adhesive that is suitible for tiling on screen after only a few days?

12th August 2011
When tiling onto a cement based screed there is no specific requirement that the screed is dry. The Code of Practice recommends that the screed be at least 6 weeks old. The reason for this is too ensure that most of the shrinkage of the screed has occurred and that the screed is of sufficient strength to withstand any further shrinkage stress withuot cracking (and therefore damaging the tile installation).
There are 'green screed' tile adhesives available on the market claiming to allow tiling onto screeds at an early age. We do not produce such an adhesive as we feel it is important to tile onto a screed with of an age where the strength and quality of the screed and workmanship can be fairly assessed.
Where Fast-Track projects require early tiling, we recommend the use of our Dry4 Binder or Dry4 Screed to produce a rapid hardening, low shrink screed.
There is currently a builders floor left on house hallway and this needs to rise 25mm. Can u advise what to put on the existing concrete floor to raise the level by 25mm prior to tiling

15th May 2008
The floor level can be raised by 25mm by the application of Professional SLC1500. This a single part self levelling underlayment which can be applied up to 25mm in one layer. Consult the product datasheet for application information.
TDS - Professional SLC 1500
we are carrying out fast track office fit-out and need to infill floor void at first floor level where stair has been removed. we are installing t-beams with insulation over and 75mm concrete screed to take carpet finish. we need floor dry as quickly as possible. what product would you recommend to reduce drying time.

18th November 2009
Instead of 75mm concrete screed, use Larsen dry4 screed, this is a proprietary hydraulic, rapid drying screed. It can be covered after 1 week.
Alternatively, after placement concrete apply Larcote DPM (2-part epoxy dpm) onto concrete and SLC 1500 @ approx. 5mm.
We are looking for a product to seal a painted concrete surface which would then allow us to lay ceramic tiles.

23rd January 2011
When tiling onto painted surrfaces it is very important to ensure the quality and bond of the paint is sufficient to support the tiling installation. Good quality gloss or epoxy paints may provide a suitable base for tiling, but cheaper floor paints and emulsion should generally be mechanically removed before tiling.
If the paint is sound, I would recommend using Larprime EU. This is a two pack solvent free epoxy primer. After mixing apply to the floor with a roller and then while still wet apply a broadcast sand scatter of dry 16/30 sand at a rate of 2kg per sq. m. Leave overnight for the primer to harden and then brush or vacuum to remove excess sand. This will leave a sandpaper like finish to provide a mechanical key for tiling.
We are proposing to use "Shake Top" hardner unto a new concrete floor that is been used to store scrap lead. It is possible that potential light acids might be present in the scrap lead, & leach unto the floor. Please advise if the hardner is suitable for said application?Will light acids cause a problem?
Will the lead react with the hardner?

2nd November 2010
Shake-top provides a very hard wearing abrasive resistant floor. As it is cement based, the floor would need to be sealed to prevent damage from the acids. Suitable sealers include Acraseal or Larseal Impregnation
We are renovating a domestic floor that has an existing pitch-epoxy surface DPM. Could you please comment on the suitability of Larcote PE pitch-epoxy for re-coating damaged and repaired areas, and then probably overcoating the whole floor with a final new surface DPM, before applying floor covering.
Many thanks.

20th September 2011
Due to apparent state of the the existing coating I would recommend removing it by mechanical means, e.g. enclosed shot blasting or grinding, to expose the original substrate.
I would not recommend applying our DPM over an existing pitch-epoxy coating.
We have been asked to look at a solution to coat an existing internal concrete flagged floor with a product that will give slip-resistant properties to the flooring. Can you advise if you would recommend anything in particular and what problems may occur, if any, due to the fact that the base surface are flags, and therefore may be susceptible to a degree of movement

7th December 2009
With the floor being a concrete surface (albeit flags) the most straightforward option may be to simply mechanically roughen the surface either by grinding or enclosed shot blasting. This will give a profile to the floor which will improve slip resistance.
In terms of a coating, either Larsen WDC or PE epoxy coatings can be applied with a sand scatter which again will provide a profile to improve slip resistance. In this case with the possibilty of movement in the flags it would be prudent to coat each flag indivually rather than the floor as a whole.
For further information ring our technical sales on 02890535427.
What is the best way to repair a 0/3mm crack x 750 long in an under floorheating 90mm thick slab prior to tiling. The slab has been laid 10 months.

27th November 2009
Cracks in floors can be repaired with a number of products depending on the width of the crack. In all cases it is important to be sure that the crack is static otherwise it may reappear after the repair is complete. The options are as follows:
Hairline cracks and crazing - Larsen Injection resin squeegeed into the cracks.
Fine cracks up to ~5mm - Largrout EP
Wide Cracks >5mm - Larfix E or Larsen Rapid Patch

04 Tiling

Are Larsen Standard and Fast setting tile adhesives suitable for direct application to aluminium heat spreader plates on underfoor heating systems?

27th June 2011
No, generally aluminium spreader plate underfloor heating systems are designed to be overlaid with timber floors. It may be possible to oversheet the heating sytem with a tile backer board which could then be tiled onto, but it would be better to discuss the options with the supplier of the heating system to get their recommendations.
can i use brown floor grout on wall tiles

16th November 2009
Yes, but the joint must at least 4mm. As our floor grout contains sand great care must be taken when used with glazed ceramic tiles to prevent scratching.
Can I use your flexible floor tile adhesive to tile a new floor over existing tiles?

10th September 2008
Yes, Flexible Floor Tile Adhesive is suitable for tile on tile applications.
It is important to ensurte the existing tiles are firmly bonded and clean. It is advisable to thooroughly degrease the surface particularly if the floor is in a kitchen etc.
Prior to tiling apply one coat of Larsen Acrylic Primer neat and allow to dry tacky before tiling.
Can i use your Impregnating Sealer for marble and travertine tiles ?

1st July 2011
Impregnating sealer is suitable for any porous stone, concrete or tile. For Marble, Travertine etc we can also supply Larsen Professional Marble Protector
Always carry out a trial area in an inconspicuous are or test the product on a spare tile before applying to entire floor to ensure the finish, appearance etc is accpetable.
Can larsen flexible fast set tile adhesive be applied when the pva sealant on concrete floor is still tacky.

21st December 2011
We don't recommend the use of PVA as a primer for cement based tile adhesives. We would always recommend the use of Larsen Acrylic Primer when required with cement based tile adhesives.
When applying the tile adhesive to the primer it is best to wait until the primer has dried clear but remains tacky, this is usually within 1-2 hours.
Can you tell me if CTA Tanking Pack is suitable for use with underfloor heating (concrete screed)

23rd November 2009
Yes CTA Tanking Pack is suitable or use with underfloor heating. However, it is important to ensure the screed is fully dry and that the underfloor heating has been tested for a least seven days before applying the membrane. An alternative and better solution would be to use our new Seri-Dec Matting which will both tank the floor and prevent vapour pressure from building up in the floor.
Gypsum based screeds must have a moisture content of less than 0.5% before covering.
Can you tile direct onto WBP plywood or do you need to use a sealer ? I will be using the Larsen flexible tile adhesive.

21st April 2009
Yes. However due to the supply of inferior grades of plywood to the market recently, we recommend that the surface of the plywood is lightly sanded and then primed with one coat of Larsen Acrylic Primer.
When tiling onto timber it is improtant to ensure that the floor is well supported and free form deflection. Plywood sheets should be ~18mm and screwfixed at 300mm centres ensuring there is sufficient support joist adn noggins and that all board edges are supported.
Can your Impregnating Sealer be used to seal grout?

18th August 2011
Yes, Impregnating Sealer is ideal for sealing grout joints. If the tile is absorbent then I would recommend sealing the entire surface. If it is non-porous (e.g. ceramic) then wipe of any excess sealer from the tile before it dries.
Hello, please let me know if you Flexible Standard Set Adhesive is suitable for use with underfloor heating covered with concrete screed please?

25th November 2011
Yes, our Flexible Standard Set tile adhesive is suitable for use over underfloor heating.
When using a standard setting product on floors please ensure sufficient time is allowed for the adhesive to harden before grouting or trafficking.
How can I remove adhesive from the back of tiles so I can reuse them

20th February 2010
Tile adheisves are designed to exhibit a strong bond to most types of tile and as such cured adhesive can be very difficult to remove. In small areas, mechanical scraping or grinding may be successful.
How much Larsen Flexible Standard Set Adhesive do I need for a 12 square metre kitchen floor?

23rd October 2011
3 x 20kg bags should be sufficient allowing for wastage.
Take care as Larsen Flexible Standard Set will take 16-24 hours to harden before the floor can be trafficked and grouted.
I am doing a tiling job in a train station onto a 12mm ply floor laid over 18mm t&g.What adhesive would you reccomend for a porcelian tile

30th July 2008
Our Professional Flexible Fast Set would be suitable for this application. It is imperative that the plywood is adequately screw fixed at 300mm centres and along edges. Ensure sufficient joists and noggins exist to prevent deflection and the underside of the floor is adequatley ventilated. The resulting floor must be free from excessive deflection prior to tiling. Consult the product datasheet and our Tiling Specication Guide before use.
i am laying limestone tiles on plywood floor with under floor heating, do I need to turn off heating and if so ,why?

23rd January 2010
It is always recommended to turn off underfloor or undertile heating before tiling. If the heating system is left on during tiling the adhesive will set more rapidly which in itself may not be a problem, however there is a greater risk that the adhesive will have skinned over before the tiles are placed. This results in a reduced bond between adhesive and tiles and in the worst cases it can result in a total lack of bond.
I am specifying a job and need your advice. It is a honed and filled travertine tile 60x40cm (very rough back) going down on sand/cement screed with underfloor heating. Grout width will be 4mm, colour ivory. What adhesive, grout and sealer is best?

26th November 2009
Adhesive - Larsen Professional Flexible Fast Set - White
Grout - Larsen Professional Stain Resistant Wide Joint Grout -Ivory
Sealer - Larsen Professional Marble Protector
If the screed is very porous it would be worth priming with Larsen Acrylic Primer
I am specifying a job and need your advice. It is an opaque 10mm thick polished marble tile 30x30cm going onto a wall around a shower, domestic use. The wall is sand/cement plaster on 100mm block. Grout width will be 1mm, colour grey. What adhesive, grout and sealer is best?

26th November 2009
Adhesive - Larsen Professional Flexible Standard Set
Grout - Larsen Professional Stain Resistant Narrow Joint Light Grey
Sealer - Larsen Professional Marble Protector
It would also be worth considering using Larsen CTA Tanking Kit
I am using the flexible standard set adhesive and preping the wall first. I am also using the pink ready made acrylic primer. do i dilute it? or put on straight?

23rd April 2009
Larsen Acrylic Primer can be used as supplied without diluting.
However, when using a cement based tile adhesive on a gypsum plastered wall it is neccesary to fully seal the wall to prevent a chemical reaction between the gypsum and the tile adhesive. This is best achieved by applying one coat of the primer diluted 1 to 1 with clean water. Allow this to dry and then apply one coat of the primer neat. Allow this second coat to dry before tiling.
I am using your larsen flexible floor grout black and I run into a problem. My white ceramic tiles are smudged with black stripes after the grout is applied. What product(s) do you suggest I should use to clean them?

11th September 2009
Often it is simply a matter of cleaning the tiles with a mild acidic cleaner such as Larsen Professional Cement Remover with a plastic, non-scratch scouring pad.
Always trial a small area first and protect yourself and sensitive surfaces when using cleaning products.
i have a customer whos tiles have lifted off the floor. after inspecting the floor it seems that she has put a layer of varnish on the finished floor to keep dust down which proably lead to the tiles lifting. she now wants to retile the floor. is there anything i can put over the varnish or would i be better to remove the varnish. would flexibilzing the floor and throuwing sand on it letting it set and brushing off the excess ans then laytexing the floor be ok before tileing it again or not. please advise

12th March 2010
The best method would be to mechanically prepare the floor e.g. grinding back to a good quality absorbent substrate. It is worth noting that the floor may be of poor quality if it was initially 'varnished' to keep the dust down. An alternative option would be to use a decoupling membrane such Larsen Ser-Dec and leave the'varnish' in-situ.
I have bought your NARROW grouting for my tumbled travertine tiles but find that the joints are nearer 7 mm. Can you suggest how I can still use this grouting? and what will be the problems, if I do?

18th September 2010
Our Stain Resistant Narrow Joint Grout is suitabel for use up to 4mm joint widths. Above this joint width there is an incresed risk of cracking of the grout and also it will be more difficult to attain a well filled grout joint.
If you are forced to use the Narrow Joint grout at widths >7mm, the only thing which you could try would be to make the grout up stiffer than normal by mixing with less water. While this may help, there will still be a greater risk of cracking.
I have had applied porcelain tiles around a bath tub tub with Larsen tile adhesive and grouted with another copmpanies grout, result stains on tiles. Help!

29th October 2009
While porcelain tiles are of very low absorptivity then often have microscopic pores in the surface. When grouted with a fine cement based grout these pores can become filled with cement film and pigments. This is particularly noticeable when the grout is of a contrasting colour to the tile.
Often it is simply a matter of cleaning the tiles with a mild acidic cleaner such as Larsen Professional Cement Remover with a plastic, non-scratch scouring pad.
Always trial a small area first and protect yourself and sensitive surfaces when using cleaning products.
I have had two bathrooms and a cloakroom refitted. The fitter used Larsens professional tile adhesive and grout to fix the tiles. Unfortunately he used the 'Dot and Dab' method to fix the wall tiles. I note from your product advice this is not a recommended method. Can you tell me the problems that could occur from using the ‘Dot and Dab’ method of fixing tiles to the wall.

28th November 2010
Dot and Dab is not recommended as it generally results in the adhesive being applied thicker than the recommended application depth and in there being a relatively low coverage of adhesive on the tile. If the tiles are well bonded, there may be no real problem. Problems generally occur when dot and dab is used on floor tiling or in wet areas, where the recommendation is for 100% adhesive coverage to the the tiles
I have over applied your 'Tile,Slate&Floor Sealer' to ceramic tiles. Is there a product to strip same and do over? I'd really be very obliged for your assistance.

10th July 2009
Tile, Slate & Floor Sealer would be quite difficult to remove once dried as it is designed to protect the underlying floor from damage. Proprietary paint stripping products may be suitable to remove it, however always trial an incospicuous area first for compatability with the substrate.
It is also worth noting that glazed ceramic tiles do not generally require the application of a sealer and indeed most sealers require a degree of porosity in the substrate.
I have recently had a porcelain tile floor layed in our kitchen.How do we remove the residue of grout and adhesive and bring the surface to a high clean finish

1st September 2009
We supply a range of Tile Maintenance products to care for your tiling installations. Cement Remover and Extra Strength Remover are acid based cleaners in the range which will remove grout and adhesive residues. The floor can then be cleaned and maintained with Clean & Shine.
I have removed vinyl tiles from a concrete floor and there is "cutback" adhesive left on the concrete. Do you have any ceramic tile adhesive that is suitable for use over "cutback" without having to remove the cutback from the concrete?

23rd July 2010
Cutback is an old type of adhesive which is based on bitumen. While cement based tile adhesives (particularly flexible grades) will probably bond well to the old adhesive, as it is bitumen based and inherenetly 'soft' we typically find that failure will occur within the old adhesive. All cement based materials will shrink to a degree on setting and this can create enough force to shear the old bitutmen based adhesive.
Our recommendation would be to remove the old bitumen based adhesive until there is at least 75% of the original, uncontaminated concrete showing, before attempting to fix ceramic tiles.
i need a adhesive fo fix some brick slips to the exterior of my house, i beleve i used some larsen quick dry floor tile adhesive a few months ago and on the packet am sure it said i could use it for brick slips,if i am wrong what can you recomend thanks

19th February 2010
Our cement based tile adhesives are suitable for use externally and would be ideal for fixing brick slips. It is probably better to use a Flexible (S1) standard setting product e.g. Larsen Professional Flexible Standard Set. This will give a long working time and allow adjustment of the brick slips.
I over applicated larsen impregnating sealent on slate floor. Is there anyway to remove the black blotches. Acetone for example

9th April 2009
Unofrtunately there is no easy way of removing Impregnating Sealer.
It is worth mentioning however, that it is unlikely that the Impregnating Sealer has caused the blothces (unless a very large over application). It is more likely that the sealer has merely highlighted some of the natural variations in the slate.
I've been asked by a client to tile a large exterior balcony area which was finished with roof grade asphalt. Do you have a product (eg. a decoupling membrane)which would gaurantee that the tiles would not lift due to the expansion and contraction in the asphalt.

14th August 2011
It is impotant to ensure that a balcony finished with roofing grade asphalt is structurally strong enough to be used as an outdoor living space.
Unfortunately, we do not have a decoupling membrane available at the moment, I suggest you contact Schluter systems.
Is Larsen Professional Stain Resistant Narrow Joint grey grout suitable for grouting porcelain laid on plywood?

25th May 2010
Larsen Stain Resistant Narrow Joint Grout is flexible and therefore suitable for grouting tiles suitably laid on correctly prepared timber substrates.
Is Larsens flexible standard set used for grouting and setting tiles

5th February 2010
No, Larsen Flexible Standard Set is a tile adhesive and is only suitable for fixing tiles, it is not suitable for grouting. We have a full range of tile grouts specifically designed for grouting applications.
My customer has bought a cement based tile adhesive made by yourselves. He has a gyvlon flow screed floor. Do you supply a epoxy primer to be used inbetween the two ?

1st December 2009
When tiling over an anhydrite floor screed, we recommend the following:
1. The floor should be dry - less than 0.5%. Underfloor heating if present should be tested for 7 days prior to tiling (this will also help to ensure the screed is dry).
2. Any laitence (scum) should be removed from the surface by brushing or sanding.
3. The surface should be primed with one coat of Larsen Acrylic primer diluted 1:1 with water followed by one coat of Acrlyic primer applied neat.
The following is a link to our specification
Tiling onto gypsum screed
Please can you advise a suitable preperation for plaster skim on walls before tiling in a shower area, I will be using larsen cement based adhesive and professional wide joint grout on travertine tiles.

19th July 2011
The first thing to check is the weight per square metre of the tiles. Plaster skim is only suitable to support around 20kg per square metre of tile and adhesive. If your tile and adhesive is going to be more than this then we would recommend either using a different tile or mechanically fixing a suitable tile backer board to the wall.
Assuming the weights are ok then it is best to use our Tanking system in the shower area prior to tiling. This is a paint on membrane and tape system which is suitable to receive tiling with a flexible cement based adhesive after 24 hours.
Please can you let me know what adhesive and grout I need for pebble
tiles in swim pool?

18th November 2010
Either Larsen Professional Flexible Fast Set or Flexible Standard Set adhesives would be suitable. For the grout, I would recomend Larsen Epoxy Tile grout.
Should I prime a plasterboard wall before tiling with travertine tiles (305mm x 305mm) and using your fast set white adhesive. The plasterboard is the green stuff used for bathrooms.

24th June 2011
Generally plasterboard (which has not been skimmed) does not require priming.
It would be advisable to check the weight per square metre of the tiles as plasterboard is only recommended for use with tiling up to 32kg per square metre (including the weight of adhesive - approx 4kg per square metre).
The grout that I have purchased states on the packaging that it is for joints of 3 to 20mm however I have elected to tile at 2mm joint spacing. I note that your latest product indicates that it can be used for 2mm joints. Can you please advise if the grout I have will be suitable for 2mm joints or will I need to purchase more? The tiled areas include floor, walls and shower cubicle.
Mant thanks.

12th March 2010
We are currently updating the packaging on our Stain resistant grouts. Larsen Professional Stain Resistant Wide Joint Grout is suitable for use in joints of 2-20mm.
We are looking for a product to seal a painted concrete surface which would then allow us to lay ceramic tiles.

23rd January 2011
When tiling onto painted surrfaces it is very important to ensure the quality and bond of the paint is sufficient to support the tiling installation. Good quality gloss or epoxy paints may provide a suitable base for tiling, but cheaper floor paints and emulsion should generally be mechanically removed before tiling.
If the paint is sound, I would recommend using Larprime EU. This is a two pack solvent free epoxy primer. After mixing apply to the floor with a roller and then while still wet apply a broadcast sand scatter of dry 16/30 sand at a rate of 2kg per sq. m. Leave overnight for the primer to harden and then brush or vacuum to remove excess sand. This will leave a sandpaper like finish to provide a mechanical key for tiling.
We have used your Stain Resistant Narrow Joint Grout between the 25mm mosaic tiles lining a swimming pool. We note that you recommend leaving the grout for 3 weeks before filling the pool. Unfortunately, because of the high water table, it is not practical to leave the pool empty for that long. Can you say what the effect will be if we fill the pool after a few days please.

12th February 2011
It is necessary to leave the grout for a minimum of 3 weeks before filling the pool to allow the grout to achieve sufficient strength to resisit wash out from the joints and resist stresses in the structure which may occur on filling.
What is the minium size grout joint with porcelain 45x45cm rectafied floor tile?

9th September 2011
Typically tiles of this type would be fitted with a very narrow grout joint of maybe 2mm. For this application we would recommend using our Professional Stain Resistant Narrow Joint Grout.
It is recommended to give greater consideration to movement joints, even in domestic situations when instally large format tiles with narrow joints.
Where in Wakefield, west yorkshire stocks larsen grout ?

2nd July 2011
If you call our Sales Manager Martin Colbey (07710864636), he should be able to locate your nearest stockist.

05 Repair

A screed in a plantroom has broken up due to the vibration of pumps. The pumps are being replaced and put on anti-vib mountings, but what product is best suited for repair to the screed.

22nd June 2009
Hevy duty floor repairs in areas subject to vibration are best carried out with an epoxy product. For small area repairs use Larsen Epoxy Concrete Repair Kit. For larger areas or reinstatment of the screed as a whole use Larfloor HDS epsoxy screed.
Advised that sandblasting too harsh to remove paint off sandstone around church windows, can you suggest another way?

9th February 2010
I would suggest a chemical paint remover. Unfortunately, this is outside our product range
Can you advise how to repair a section of an insitu reinforced concrete bay window lintel which has spalled of concrete to the exterior vertical face and soffit exposing the reinforcement bar for approx 1.2m along its length. The height of spall is approximately 150mm and 60mm deep. Note the reinforcement is badly corroded so a treatment to prevent a re-occurrance would be required.

25th March 2009
Mechanically remove all loose and friable concrete and wire brush or similar the rebar to remove corrosion. Ensure the surface is free from dust and other forms of contamination. Ensure the rebar and concrete is of sufficient structural integrity to fulfil duty.
Mix and apply Larcem RP to the exposed rebar and allow to harden. Mix and apply Larcem PA to the entire exposed surface and while still tacky (within approx 15min) apply Larcem 1450 Lightweight Repair Mortar.
When the 1450 has sufficiently hardened, Larcem Fairing Coat can be applied to give a smooth uniform, durable finish.
could you tell me your best product to repair concrete that the frost or grit has taken the top off some parts are maybe 8to 10 inches long and 1/2 in deep some are 2 or 3 ins by1/4 if you could tell me your best product i would be most grateful.

15th March 2011
Firstly it is important to remove all loose or friable material until a solid surface is reached. Then Larsen Professional SLC2050 External self-levelling compound can be applied.
Hi there,- in the tech datasheet for larcem 25 SBR it is recomended that chemcrete 100+ be used as a super plasticiser when producing microconcrete. would there be any problem using chemecrete HP3 super plasticiser in its place?

12th January 2012
Chemcrete HP3 superpalsticiser is also suitable. Make sure the superplasticiser and the SBR are added separately to the mix.
Hi, I'm looking for a product that will seal running water through a small gap in a concrete block wall. The water is running from the water table into the outlet side of a septic tank. Would you stock a suitable product?

4th November 2008
Larsen Leakplug is a ultra quick setting (~60 sec), waterproofing compound for repairing water leaks. When mixed with water a paste is produced which can be used to seal water leaks in concrete, rock, blockwork, brickwork, manhole rings etc. It is ieal for use to stem the flow of leaks before tanking takes place with Larpruf CG, Larsen 3:1 Tanking Mix or a Larsen Integral Waterproofer render.
I am looking for a product to seal a 15 mm gap between a first floor patio and a external wall

29th January 2010
A flexible sealant should be used either Polyurethane LM 15 or MS-Polymer (Bond & Seal)
I am renovating an old red brick house that has some structural cracks. What grout do I use to repair the cracks with?
Also an old I beam is rusting. What product can I apply to retard the rust?
Thanks

29th April 2009
Structural cracks in a house should be fully investigated by a professional surveyor prior to carrying out any repairs. Depending on the cause, nature and size of cracks there a number of options as to which product/method to employ. At the simplest, the repair required may be only aesthetic and the most severe the wall may require 'stitching' or the wall needing underpinned. Until this is known a product cannot be recommended.
Depending on the location of the I beam the simplest option may be to blast or wire brush back to bare metal and then painting the beam with something like Black Bitumen Paint.
I currently have external ceramic tiles which are beginning to lift. Have you any adhesive and grout which is suitable for external ceramic tiles which are on a concrete base?

30th March 2010
All our cement based tile adhesive are suitable for external use, however due to the risk of thermal expansion we would always recommend using a flexible tile adhesive exteranlly, e.g. Larsen Professional Flexible Fast Set.
I have concrete imprint on my driveway.The paint has lifted/flaked in areas and
I want to re paint it.The colour is black.Where in Ashbourne,Co.Meath ,Ireland are the stockists of Larsen's paint/sealer?

12th July 2010
Normally, printed concrete driveways are not painted, rather the concrete is coloured and then the surface is sealed with a product such as Larseal Super or Larsen Acraseal. We do not sell coloured paints or coloured sealers for this application. For details of where Larseal Super or Acraseal can be purchased contact our Dublin Office on 018348255
My garage window lintels are badly worn and water is penetrating. How do you recommend repairing or sealing?

15th August 2011
The lintel could be repaired / refaced with or Feather Edge or Rapid Patch repair mortars. Or sealed with Larsen Water Repel or if dusty and friable Larsen Impregnation epoxy sealer.
Repairing plaster around old windows. Is SBR Bond (Larcem 25) suitable?

26th November 2011
SBR Bond (Larcem 25) can be used both in the render and as a priming slurry to greatly improve the adhesion and durability of any repair.
We have a project where damp is penetrating a period home 225mm solid brick wall construction. We are lining walls internalls, but do you have a spray on invisible product to apply to the bricks externally to waterproof them?

16th May 2011
Larsen Water Repel is a solvent based metallic stearate solution designed for wateroofing brick, block and natural stone.
What is the best way to repair a 0/3mm crack x 750 long in an under floorheating 90mm thick slab prior to tiling. The slab has been laid 10 months.

27th November 2009
Cracks in floors can be repaired with a number of products depending on the width of the crack. In all cases it is important to be sure that the crack is static otherwise it may reappear after the repair is complete. The options are as follows:
Hairline cracks and crazing - Larsen Injection resin squeegeed into the cracks.
Fine cracks up to ~5mm - Largrout EP
Wide Cracks >5mm - Larfix E or Larsen Rapid Patch
What is the best way to repair a concrete silo floor, we can only have a total thickness of new material of 50mm,on top of the existing reinforced concrete,which is worn, and has a lot of 20mm exposed aggregate

4th March 2010
A pumpable self levelling compound could be used (Professional SLC 1900) or alternatively a cheaper option would be to use a polymer modified screed bonded to the existing concrete. This can be achieved with Larcem 25 (SBR Bond).

06 Screeding

A section of a concrete floor requires a self levelling screed which is allow for a depth of 12mm in places?

10th August 2011
Larsen Professional SLC1500 is suitable for use from feather edge to 25mmm and should be suitable for you application.
Can Larsen 1500 SLC be laid onto WBP plywood to make up floor levels so the actual depth of fill is less than 25mm?

25th June 2010
Larsen Professional SLC1500 is only recommended for use on solid substrates such as concrete or screed. For application onto suitable fixed and prepared plywood we would recommend the use of Larsen Professional SLC1550 which is a fibre reinforced leveling compound. To further strengthen the floor a reinforcing mesh can be laid into the product.
do we need to use a special latex screed on top of a floor treated with the speedo accelerator

29th September 2009
No. Once hardened, Speedo screed can be treated as any other, so any common levelling compound may be used.
Do you have a floor screed product that canbe laid 40 thick on board insulation?

9th July 2009
Depending on the application there are a few options. If it is a domestic situation, typically with underfloor heating and a flowing screed is possible, I would recommend Larsen floTherm Liquid Screed.
Alternatively, for a fast drying semi dry screed, Larsen dry4 Binder (with the inclusion of Larsen Fibrescreed) can be mixed on site and laid like a traditional screed.
how do i mix the Flotherm liquid floor screed.

10th October 2011
Flotherm liquid floor screed can be purchased readymixed from numerous concrete suppliers throughout the island of Ireland.
For site mixing use a good, clean screeding sand free from lignite and with a low organic content and mix.

A typical starting point mix design is:
600kg Flotherm Binder
1200kg sand (dry weight)
330L water (total water)
The flow should be checked before pumping commences and should be in the region of 230-250mm.
Mixing can be carried out with a suitable pump mixer.
For more information contact our Technical Department
I need to apply a lightweight screed to a fiberglass deck thickeness 5 upto 12 mm

28th May 2010
Unfortunately we do not manufacture lightweight screeds at this time.
I need to screed an existing garage concrete floor to level (2-3mm) & apply decorative finish(can be resin based but needs to be coloured). Can you recommend a product?

25th August 2009
While a standard levelling compound may be suitable, I would recommend the use of Larsen Professional SLC 1500 as the levelling compound. This high quality leveling screed can be applied from next to nothing up to 25mm and will provide a very good finish for the application of decorative finishes.
In terms of finish we have two suitable products -
Polyfloor - a medium duty single pack floor paint
WDC - a two pack epoxy coating offering superior wear resistance
Both are avaialbel in red, light grey and dark grey as standard.
i would like to know if i can mix the flo screed myself by using a water drum & mixer which we use for mixing plaster

4th January 2012
In theory yes it could be site mixed in this way. However, in practice it much better to use a pump mixer to ensure a continuous supply of material as the floor is poured. If you would like to talk to someone regarding our Flotherm, call Jonathan Mooney on 07710864634.
I'm being given conflicting advice from tradesmen as to whether self levelling screed is strong enough to be used to smooth out an exposed concrete floor prior to painting. Floors are all internal (ie foot traffic and furniture only). Any advice as to the best type of screed / paint to use would also be appreciated. Thanks

16th February 2011
In order to provide a wearing finish a suitable self levelling screed must be used. Our Professional SLC2000 Industrial is suitable for providing a wearing finish without further coating, however the application of a sealer is recommended to reduce the risk of staining. Professional SLC1500 is suitable to receive a suitable floor coating preferably a 2 pack epoxy or equivalent.
My customer has bought a cement based tile adhesive made by yourselves. He has a gyvlon flow screed floor. Do you supply a epoxy primer to be used inbetween the two ?

1st December 2009
When tiling over an anhydrite floor screed, we recommend the following:
1. The floor should be dry - less than 0.5%. Underfloor heating if present should be tested for 7 days prior to tiling (this will also help to ensure the screed is dry).
2. Any laitence (scum) should be removed from the surface by brushing or sanding.
3. The surface should be primed with one coat of Larsen Acrylic primer diluted 1:1 with water followed by one coat of Acrlyic primer applied neat.
The following is a link to our specification
Tiling onto gypsum screed
we are carrying out fast track office fit-out and need to infill floor void at first floor level where stair has been removed. we are installing t-beams with insulation over and 75mm concrete screed to take carpet finish. we need floor dry as quickly as possible. what product would you recommend to reduce drying time.

18th November 2009
Instead of 75mm concrete screed, use Larsen dry4 screed, this is a proprietary hydraulic, rapid drying screed. It can be covered after 1 week.
Alternatively, after placement concrete apply Larcote DPM (2-part epoxy dpm) onto concrete and SLC 1500 @ approx. 5mm.
What product do I seal concrete with to allow me to tile after 3 days curing

7th April 2010
Current recommendations and best practice suggest concrete should be 6 weeks old before tiling. This allows the concrete to have gained a suitable level of strength and dryness and ensures that the majority of any early age shrinkage and associated cracking has taken place before tiling.
The main risk from tiling too early is that drying shrinkage cracking may occur in the concrete leading to cracking or debonding in the tiling installation.
If you are forced to tile onto concrete this early we would recommend using a decoupling matting system, such as our Seri-Dec. These systems help prevent stresses from the substrate being transmitted into the floor finish.
For further information consult our new tiling brochure or phone for further technical advice.
Your "Dry 4 Screed" has been specified to construct a 6m x 6m x 100mm base on an existing concrete floor. Can you tell me what quantity of your product I need to order. Also what proportion of water to SBR Bond (Larcem 25) you recommend. Should I use a Mix of Larcem 25 and cement as a bonding agent to the existing floor and new base

9th November 2009
This would require approximately 275 x 25kg bags of Dry 4 Screed.
Larcem 25 is usually diluted 1 part with 3 parts water to be used as a gauging liquid or mixed 1:1 with cement when used as a bonding agent for bonded screeds.

07 Renders and Plastering

best method of applying render to concrete lintels above widows and best mix

12th September 2009
Ensure the concrete is free from dust, mould oil or any other contaminants. Apply a bonding grout of Larcem 25 mixed 1:1 with cement and then immediatley plaster with Mix A as described on the Larcem 25 datasheet.
Can I apply new rendering directly on top of an existing small pebble dash which is in good condition or must I remove it first?

2nd May 2011
It is always best practice to remove old renders, especially when they are pebble dashed. Otherwise there is a risk that the original render will not be sufficiently strong to support the weight of the additional layer of new render.
Do you have a product that will allow me to render directly onto a concrete blockwork retaining wall. The retaining wall is external... my concern is potential spalling of the render in the future

11th March 2011
Larcem 25 SBR Bond can be mixed with cement to provide a priming slurry. This should be applied immediately before the scratch coat with the scratch coat applied wet on wet. This will ensure a very strong bond of the scratch coat to the substrate. Further, Larcem 25 SBR Bond can be mixed with the render to improve bond, flexibility and ultimately crack resistance.
Do you have a solution for waterproofing a painted roughcast dash render on a solid house external wall.

12th February 2010
Unfortunately no. Larsen Water Repel and Larpuf SWR are both surface applied masonry water repllents, however both products must be applied to a porous surface in order to function.
This leaves you with two options, either remove the paint and apply a masonry water repellent or alternatively simply repaint the wall with a suitable water repllent masonry paint.
Do you market/recommend a suitable sealer product which would prevent a soot staining problem penetrating through a plaster skim finish on an interior wall of Church Building

12th May 2009
Unofrtunately, I do not think our sealer would be suitable for this application. However there are specialist paints on the market which can prevent damp and staining showing through the top coat paint.
House, 14 years old with red algea staining on external wet dash roughcast render. Do you have a product that can remove this without seriously damaging the render

23rd June 2009
Larsen Concentrated Algicide will deal with most algae staining. Simply dilute the product as directed and spray onto the affected area and allow to dry.
In heavily contaminated areas the area should be powerhosed to remove heavy deposits and then sprayed with the diluted algicide as above.
I have to plaster an old block wall that is 20 years old and is covered in red algae on both sides.Is there a product that will guarentee to get rid of the algae and the plaster not to blow off.

17th July 2010
Larsen Concentrated Algicide can be used to treat algal growth prior to plastering. For best results remove as much groth as possible by power washing etc, then apply Larsen Concentrated Algicide as directed.
Larsen Concetrated Algicide will have no effect on subsequent plaster or paint coatings.
I need to render a Victorian brick tank to make it water proof. The current render needs replacing. Can you reccommend an additive or a render and if neccessary a surface treatment.

The water stored is rain water and is there any way to do this for the water to be safe for human consumption?

16th March 2010
Unfortuantely if this is for drinking water we do not have a suitable product. The render or additive in this case would need WRAS approval.
If the water is not for consumption then there are a number of tanking options available including Larsen Integral Waterproofer, Larpruf CG and Larecm 25 SBR Bond. Contact our Technical Sales (a.duffy@larsenbuildingproducts.com) for further advice.
seeking advice on how to prevent cracking in a narrow band of external render applied to metal lath fixed to timber beam, dimensions 0.3m deep by 3.5m long? i'm thinking expansion joints, glass fibre mesh and polymer additive.

20th October 2010
Your idea is correct, add Larcem 25 SBRBond to the render mix (dilute 3:1 with clean water and use this as the gauging liquid). The inclusion of reinforcing mesh and a separation joint will further reduce the risk of cracking.
the soft stone surrounding a bay window in a 1900 house has cracked in places and the surface come away, I need to rebuild the original profile with render and then paint. do you have a product to apply before commencing the rendering or to mix with it/ the surface of the stone is very soft.

21st March 2010
If the stone is very soft, the best option would be to remove it and replace with a similar material this would probably also mean bedding in with a Hydraulic Lime Mortar.
If the damage to the stone is not siginificant the profile could be raised with the application of Larsen Rapid Patch fast setting repair mortar.

08 Others

A contractor has used Larsen Wood Preservative to treat timbers in a house and has splashed and smeared it on the plastered walls of the rooms (green colour). Can you recommend a product to block the stains and stop them coming through freshly applied paint?

4th May 2011
The first thing to do is to ensure the Wood Preservative has dried, as it is solvent based, any residual solvent could affect the bond of the paint. Once it has dried any commercially available stain blocking paint (such as products available to block nicotine stains) should be sufficient to block the colour. The dyes used are solvent soluble not water soluble and so should not migrate through a water based paint.
Can I use feather edge to repair a floor with underfloorheating

4th February 2010
Yes, Larsen Featheredge is suitable for use on a cement based floor (concrete or screed) with underfloor heating. It is not suitable for repairing gypsum screeds.
Ensure the heating is turned off 48 hours before application and allow 24-48hours before switching the heating on.
Can the Polyfloor Garage Floor Paint be used on a gypsum based (calcium suplphate) floor screed? If so, are there any special precautions that need to be taken? e.g. when tiling where the floor had to be double primed?

22nd September 2011
Polyfloor would probably be okay for use on a gypsum screed, but it would be better to use a water-based epoxy coating like our Larcote WDC. Water based epoxy coating tend to exhibit a better bond to gypsum screeds than solvent based coatings.
Normal paint preparation methods are all that is required, if the surface has laitence, then it would be recommended to grind/buff the surface and vacuum before coating. The first coat of WDC can be diluted with up to 10%water for use as a priming coat. The screed shoud be dry prior to coating.
Can you provide a product sealer to apply on to a bradstone masonary block wall to form a seal againest water ingress

5th November 2009
Larsen Water Repel can be applied to most absorbent surfaces such brick, render or in this case Bradstone block and will provide a water repellent seal against driving rain.
Water Repel must be applied to a dry surface in dry conditions.
An alternative is Larpruf SWR which is a water based silicone type water repellent.
Do you have a product which would safely remove Bitumen from soft red brick please?

1st December 2009
Remove as much as possible by scraping or other mechanical means. the remainder can then be softened or dissolved by the application of white spirits or simiar solvents and blot off with clean cloth.
It will be difficult to remove the bitumen completely from the brick and there is a risk that the solvent may carry the stain deeper into the brick so carry out a small trial first.
Do you have a suitable product to repair damaged wood such as thixopropic 2-pack epoxy

1st February 2012
While we don't have a specific wood filler, we have a couple of products which might do the job - Larcrete PM Polyester Mortar and Larfix E Epoxy Adhesive and Filler.
Hi, I'm about to build a timberframe house with a basement area within shuttered retaining walls, the specification includes a membrane on the inside of the walls (Newton 500) but nothing on the outside. Some of the formwork contracters I have spoken to say there should be a coating or membrane applied, one has suggested a paint on black bitumous coating which they use on bridges, I have looked at your website and find a simple bitumen paint but also Larcote PE. Even if not required I would like to ake a belt and braces approach and apply something to the outside before the backfill - what do you suggest/recommend ?

8th June 2010
Generally, when a membrane/drainage system is specified, there is no requirement for another waterproofing system. It may be worth talking to the membrane manufacturer at www.newton-membranes.co.uk.
Larsen Black Bitumen Paint will offer a degree of protection from water ingress, but like any paint coating it may get damaged during backfilling. Another option would be to apply Larpruf CG to the external wall. This is a cement based waterproofing slurry which would greatly reduce the passage of water throught the wall.
The most important factor would be to ensure that the walls are constructed using best concrete prcatice and that great care is taken over details and to eliminate the risk of cracking.
I am linking an old concrete foundation to a new one with rebars by drilling the old and inserting the bars. Would any of your epoxy products be suitable for fillings the holes to satisfactorly anchor the rebars in the old foundation?

23rd March 2009
Our product Larfix E Epoxy Adhesive is routinely used for similar applications. After drilling the holes, they should be blown out with an airline to ensure they are dust free. The hole should then be partially filled with Larfix E mixed as directed and the rebar pushed in with a twisting action to ensure full contact and absence of voids. REmove the excess Larfix E from the mouth of the whole before set.
I have a large timber barn which is in good condition. The site is reasonably exposed, particularly the southwest side where the prevailing winds come from.......I need to decide which product to use i.e. Lardec, Lardec 24 or Creocoat. Can you advise the difference between Lardec and Lardec 24? How many coats would you recommend? Do you recommend an annual maintenance coat?

13th November 2009
Depending on the type of timber and exposure conditions it may be advisable to first treat the timber with 2 coats of Larsen Clear Wood Preservative.
Once this has dried the wood can then be stained as required. Lardec 24 has higher resin solids than Lardec (and is therefore more durable) and this would normally be applied in two coats in exposed conditions. Maintenance coats can then be applied as required and this will greatly depend on the exposure conditions but would typically be every two years.
I have window cills, 35 years old, which have been pained over the years with santex, oil based paint and latterly with exterior masonary paint. Those exposed to the sun all day flake over time. Exterior paint gathers soot spots and is difficult to keep clean. I am currently cleaning them down to concrete which still has a smooth sutface and only one of 13 has some slight spalling. can you recomment a total treatment which will be durable in sunlight, smooth for cleaning and white. Someone suggested floor paint. Would this do?

24th August 2011
I would recommend you talk to a paint manufacturer for advice on the choice of paint. I do not think floor paint would be suitable.
As with most things the key is in the preparation. It would be advisable to ensure that they are stripped back to bare concrete, if using a chemical paint stripper, ensure they are also well washed to remove any residues. Remove any loose or friable material and dust.
Using a suitable repair mortar (e.g. our Feather Edge) re-face the surface to leave it uniformly level and smooth.
Depending on the paint used a water repellent primer or priming coat of paint would be recommended.
I wish to use your woodworm treatment solution. I want to know what type of respirator to use as i will be applying by spraying - I have a full face respirator I just want to know what the correct type of filter to use with your product as I will be applying in an enclosed area.

20th August 2011
An organic vapour filter should be suitable. It would be advisable to inform the supplier of the filter of the product details to ensure the correct grade is supplied.
We would always recommend trying to ensure there is also sufficient local ventilation / extraction when working in enclosed areas. If this is not possible an air fed respirator would be advisable and also to always carry out a risk assessment.
i'm looking for a jointing sand stabilizer in your product range?

24th October 2008
We have a specific product for this application - Larsen JointSave. This is a water-based polymer latex which will soak into the jointing sand and bind it together.
Alternatively application of Larsen Polyseal will bind the jointing sand and seal the paving to enhance and protect.
I'm looking to purchase a fire retardent expanding foam to seal openings in walls where cables and pipework have been installed. I need a fire retardent foam but I want to make sure we purchase a suitable product. This is for use throughout the site but also in a boilerhouse and electrical switchgear room. Can you recommend a suitable product that meets any applicable Building or Fire Regs. Thanks.

21st July 2010
Larsen Fire Retardant Expanding foam is a one component polyurethane foam which is designed to make a fire retardant seal between ‘stony’ construction parts.
It is used to produce a high quality rigid polyurethane foam which bonds, seals and insulates most construction materials offering a fire rating of up to 80 minutes. The cured foam is resistant to most chemicals.
Larsen Water repel has been recommended for one of the external walls on my mothers house. There is Virginia Creeper on most of the wall. The installer is going to remove the creeper before applying Water Repel. Will the product be effected by the creeper growing back over the wall in time?

17th June 2010
Larsen Water Repel once dry should not damage the Virginia Creeper. However, it will render the facade water repellent and as such the wall may be less suitable to sustain the growth of the plant.
Larsen Water Repel has been used on my house to prevent ingress on rain water into the brick work. The application was done in windy weather and there is still some water coming through.
Should Larsen Water Repel be used for this type of application?
Can Larsen Water Repel be applied by brush rather than spray?
Can Larsen Water Repel be cleaned from glass windows and also self cleaning glass?

14th December 2009
Larsen Water Repel is a surface applied masonry water repellent designed to reduce the penentration of driving rain through brick, block, render or stonework. Depending on the porosity of the masonry, 2 or more applications may be required to ensure adequate protection.
Larsen Water Repel can be applied by spray or brush to dry surfaces. When applying, best practice should always be followed and this would mean not applying by spray during windy conditions due to the risk of overspray.
Overspray etc of Larsen Water Repel is difficult to remove from glass and other surfaces and this should always be avoided.
Plaese advise on how to remove residue from cured easy foam (expanding filler and sealer) on foil coated pvc windows.

6th March 2011
Cured expanding foam should be mechanically removed, i.e. carefully scraped off. Small amounts of residue may be softened and srubbed off with alcohol or similar. Always check to ensure the solvent used (alcohol) doesn't damage the substrate (the frame).
We have a contractor who has used Larsen Wood Preservative to treat existing roof timbers. He has only applied one coat and your instructions asks for two coats. He has applied a very liberal coating and by our calculations he has achieved the same loading. Is this okay?

21st December 2010
The important point is to ensure a suitable concentration of active ingredient is achieved within the timber. This can be achieved by painting, spraying or dipping. The application methods for our product are based on recommendations for this type of product as detailed by the HSE.
We use alot of timber to manufacture various crates/crating systems. We are looking into a sealant/preserver in case customers leave timber (or ply) crates outside in all conditions. Would you have any ideas?

26th June 2008
Larsen Wood Preservative (Clear) can be used 'industrially' for the preservation of timber. The easiest method would be to spray (2 coats) or ideally dip the timber (~1 hour) to be treated. The timber to be treated should be as dry as possible to allow penetration of the preservative. Always test a trial area first. Please be aware that this product is solvent based and so adequate health and safety precautions should be taken as required. I would advise carrying out extensive trials with any plywood as the solvent may affect the glue binding the layers of ply.
What product can be applied to rendered external walls disfigured by rain water running off concrete coping stones

5th November 2011
This is normally a result of dirt carried in the water penetrating the surface of the render during rain. Often the best way to prevent the problem is to ensure all drip grooves and related detailing is such to prevent water running off the coping or sill directly onto the render.
Where this cannot be prevented or where the problem still exists, the application of a stain resistant impregnation treatment such as Larsen REPEL 38, can greatly reduce re-occurance. Furhter, after the application of REPEL 38 to a surface both water and oil based staining will be much easier to remove as well as being less prevalent in the first place.
What typer of sealer would you recommend for sealing concrete roof tiles, some type of sealer that i can spray on

20th April 2009
We do not have a specific product for application onto in situ roof tiles. There are products available on the market which provide a full weather proof, rubberised coating of tiles and slates in situ and companies which carry out the supply and fit.
If you only require to seal the surface to reduce moss growth etc, then the application of Larsen Path and Patio Sealer should be sufficient.