Tiling Question

Can i use plasterboard (green paper) on top of plywood as flooring?

Hi I am installing a new kitchen but I wanted to tile the whole floor first. I live in a flat so wanted some advice. The floor is not cement based or anything. It is just floor boards so it is flexible. I thought I would put 18mm softwood plywood and then moisture resistant plasterboard on top and then tile over that using Mapei flexible adhesive and grout. Am I going about this wrong?

i came across this in terms of using PVA on plywood. http://www.ultimatehandyman.co.uk/tiling/diy_Tiling_Why_not_to_use_pva.htm

4 Answers

Best Answer

Yes do not use PVA its a no no use SBR I wish contractors would stop advising on this, stuff is no good for tiling!

Answered 15th Sep 2012

A. G. Fright Tiling Specialist

Member since 28 Feb 2011

YES you are going about this wrong! Plasterboard is for walls and ceilings NOT for use as a floor covering. I would advise either covering the original flooring with 19mm moisture resistant t&g flooring which is to be screwed to the original flooring at about 300mm intervals, then a coating of pva, and then tiles on top of that using flexible adhesive and flexible grout OR remove the original floor boards screw the new floor sheets as above to the joists (making sure you miss any water or gas pipes and electric cables) a coating of pva and then tile using the flexible adhesive & grout. the first option would increase the height of the floor by about 35mm depending on the thickness of the tiles, the second option which is more work but gives the best results by keeping the floor at the correct height is the better of the two. No doubt you have seen what happens to plasterboard if it comes into contact with water, it swells and starts to crumble, imagine if you had this type of covering under a lovely tiled floor and 6 months down the line moisture was to get under the tiles? DO NOT use plasterboard as a floor covering.



Regarding your PVA doubts,,, the article link you have added refers to 3 products, Ardex, BAL and Nicobond,
in your original question you stated you were using Mapei, if you have any doubts then you should contact Mapei and ask to speak to technical support. We can only give advice regarding the work we do as builders and the way we work to gain the end result, all builders are not the same but the products we use are the same. I have used PVA for years to seal walls and floors prior to tiling without any issues for both domestic and commercial work.

The other massive bit of advice i would give to any DIY'er is, if you dont know how to do a job then employ someone who does, if it then goes wrong due to the materials they used it will be down to the builder to put it right not you!

Answered 7th Aug 2012

Mick's Property Maintenance

Member since 3 Jan 2009

i would not advise putting plasterboard on the floor. Plasterboard is for walls
Only! It's composition is not strong enough for a walking surface! It is not very strong against compression.

18 mm ply is more than enough! Use the best quality you can find ! not the soft wood ply, but the strong one in with layers of ply in it...
all you need on top is PVA, and make sure you screw it down with appropriate screws! one should know what he is doing. Than the PVA, than Mapei flexible!

Make sure the adhesive is the appropriate one for the tiles you have (porcelain , slates, ceramic, etc.)
All the best!


Answered 8th Aug 2012


Member since 15 Sep 2010

If you are using ply you need to use only WBP certified. (The WBP stands for waterproof and boil-proof). Use 18mm sheets screwed down every 30cm and laid in an interlocking pattern like brickwork. The back and edges of the sheets should be sealed with a coat of SBR primer available from tile shops.
- don't use plasterrboard on the floor
- don't use PVA. Its crystals WILL re-activate when exposed to water content of the tile adhesive and weaken the bond
- ensure the deflection or flexing of the floor is eliminated before doing any tiling
- Mapei flex adhesive and grout should be fine. Measure accurately when you mix and if using a paddle on a drill - use low speed under 300rpm
Good luck

Answered 5th Sep 2012

GID Tiling & Repairs

Member since 20 Sep 2010

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