Plying out a floor

[davy583]

Hi again all,



When plying a floor to tile over dose it matter witch wayyou lay the ply I.E. along and floor boards or across the boards. Also witch isthe best ply to use.



Many thanks

 

[Stewart]

I always lay it across the boards in a large room and also stagger the joints. You need to use an exterior grade ply, normally wbp and at least 18 mm thick. The sub floor still needs to be deflection free and I leave a 2 mm gap between the sheets. I always overboard my ply with hardie, no more ply or a decoupler. If the floor is in good condition and is deflection free, then you could just use the hardie or no more ply, but with floor boards, they do need to be in good condition.

 

[Rich]

Brilliant advice above.

I would add that I like to seal the underneath of the ply with a PVA mix before fixing them down, this will help protect the ply from any moisture from under the floor.

Have you thought about using a backer board instead? have a read through the link below is you want some info on them


Plywood floors...

 

[White Room]

Pva has no place in tiling, I would advise sbr.

 

[Aston]

its also worth while pointing out, that when you screw into your floor boards, you need to try and get screws into the joints were possible and not just fastened to the floor boards? obviously, watch out for water and electrical connections!!

you also need a perimeter expansion gap around the edge of the room.

agree with beam regarding sealing the underneath and sides of the ply with sbr or suitable acrylic primer

 

[Rich]

Fair enough, I would never advise using pva for anything that came into contact with any tiling materials but think it would be fine for sealing the underside of the ply but, agreed, sbr would be better.

 

[Aston]

i know were rich is coming from. you'd think that pva would be ok on the underneath of the ply but all it takes is to screw through a water pipe and cause a burst and the underneath of that ply is going to get soaked at high pressure for at least 3-5 minutes or the time it takes to turn off the water.

once water has penetrated through the pva and soaked the wbp ply enough, then you have the possibility of it blowing and expanding the surface which affects the tile!. then youve got future problems.

i know pva was used for years and it might seem a bit over the top at times to insist on avoiding it but tilers have to be bang on top of any situation that could cause a failure and avoid being held accountable or even worse, sued, so my advice for any new or old tiler is avoid pva in any form of tiling or prep work...

theres so many areas that we cant control 100% control in tiling, so lets make sure we get the areas we can control right.
hope i dont come across as patronising in this reply, i just want new tilers to be aware of what can happen.

ed

 

[Rich]

Bang on Ed, good point, well made. Couldnt agree more