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Do i have to lift all my tiles pva and start again or is there anything else i can do to salvage this?

I am tiling my living room, 23 sq m. It is split into two halves, the top seems spot on, I am having a problem with the bottom half, one corner in particular. I have put plywood down prior to tiling, however did not PVA this (is this essential?). I have been using a flexible adhesive suitable for floor and walls. My problem area is one corner where the ply keeps bubbling, warping, flexing not sure the correct term, but you get my drift, this results in tiles lifting. I removed tiles and used new sheet yesterday, same problem tonight. I did not PVA the top half and I am not having any problems there? Do I have to lift it all and PVA it or is there anything else I can do to salvage this and keep costs down? Thanks guys

10 Answers from MyBuilder Tilers

Best Answer

First of all you need to use 12mm ply or 18 ply on a floor any smaller will breake and will not do the job

second PVA is not recommend on anything you tile on, as PVA only sticks to the timber, you need a tile primer like BALE or MAPIE or ARDEX brand to name couple thats to get to a true fixing

third screws should be 15cm to 20cm apart longer enough to get threw the ply and the flooring underneath and you should aslo apply grip fill under neath it to make sure its not moving.


Answered 2nd Jun 2011

When you say you have laid ply, what base is the ply covering. if its screwed down sufficiantly and then primed with an acrylic primer youll have no probs at all.
If you use pva it will result in the tiles lifting. Pva forms a barrier that will lift straight away. Acriylic primers soak into the ply slowing down the cure of adhesive and stops the moisture being sucked out the adhesive to quickly resulting in a premature cure that wont bond. almost the same as trying to lay paving with a really stiff dry mix it just wont stick to anything.
If your plying over anything other than joist floorbaords or chipboard then you have a problem.


Answered 30th May 2011

Never use PVA in prep for tiling.
Depending what you're laying your ply over, is it not possible to replace the ply with cement board?
much better surface to tile to.


Answered 5th Jun 2011

The latter advice above is more proffesional, never use PVA (Acrylic or SBR primers are the best), cement board is sound advice.
My advice is;
Use a powdered adhesive (Fleixble) referred to as single part, a standard flexible will be classed as S1 which under test condition will flex up to 5mm, a latex and or rubber crumb adhesive are generaly class S2 which would flex over 5mm, however this is a lot more expensive.
Cement board if you can get it, again fixed in accordance with manufacturers instructions, (you will get a leaflet at your purchase point), this will generaly mean stick with there silicone/glue, and then screwed down at 20cm (8") intervals.
Walk on the area before tiling and after boarding, if you can feel any movement or hear any creaking it is still moving. If you can't find cement board as thick a ply as possible.
If you are finding after this the tiles are still lifting, look for cracks in the adhesive bed this is where the problem is. This can be got over with a further matting or decoupling mebrane, but thats for another day! and a hole new question!


Answered 13th Jun 2011

Hi, What sort of ply are you using?


Answered 30th May 2011

Hi. It could be that the ply you have used is too thin or only general use ply where as should be at least WBP ply and the thicker the better. The ply should always be coated first with an acrylic primer or PVA to seal the sub floorwhich will help adhesion. I would sugest at least 12mm WBP ply glued and screwed down at 150mm centres, coated with primer and then tiles laided using a 2 part fast set flexible adhesive. Hope that helps

TSH Builders


Answered 30th May 2011

you haven't mentioned anything about screws, have you put any in?? if not you need to and you need to put lots in, approx 1 every 15-20 cms apart all over, as it will bubble otherwise, which will make the tiles come up. Make sure they are galvanised and and no longer than 1 inch as you will be in gander of hitting pipe work. Use at least 6mm marine ply, no thinner and make sure you leave a gap from the edge of the ply to the edge of the wall, approx 10-15 mil.


Answered 31st May 2011

Hi Gary,
Yes you should have used a thick mix of pva, also the floor ply quality does make a difference/ marine ply- althought more expensive has a stronger bond between the layers. If you are laying on top of joists you need 19mm ply/ onto floor boards you need 13mm, lots of screws- but make sure theres no PIPES!
Hope this helps you?
Thanks Graham


Answered 30th May 2011

Not sure what u mean by bubbling/
warping, is this the ply? it needs to be at least 6mm thick any thinner and it will move under weight. Try to use a sealant on the untreated timber and use anodised screws or galvnised nails, bright steel etc will rust. For your adhesive use flexible adhesive(powder mix), instead of water use latex (Keraquik or similar) and again when you grout, use latex and grout powder not water, that should it. Use a notched trowel and not dots on the corners, twist the tiles into place.


Answered 30th May 2011

Could not agree more i always use Bal bond used it for over thirt years no problem sounds like shuttering ply was used


Answered 1st Jul 2011

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