Setting Out condition of plyboard

[tactile]

2 questions really.
i know a few tilers who use pva to seal plyboard. Is this safe or really not recomended?

Also if i was to tile onto ply board that had been PVA'd and partially tiled onto with ToppFix flexi adhesive and the tiles then removed and Adhesive scraped off. Is there a primer that would recover all that so i can retile using the same ply? or should i insist on new ply?

i hate getting jobs that other people have started!!!

its 12mm ply on a 25mtr floor. with 60/60 porceline tiles.

[Rich]

No!! If PVA has been used, the ply needs to be taken up and replaced. The ply also needs to be min 15mm thick. Get the new ply down and then you will need to have a look at the adhesive to see if it needs to be primed (some dont). If it does then use the primer made by the same people. I use 2 part adhesive when tiling onto ply or I overboard with a backer.

[mikethetile]

12mm is insufficiant for overboarding anyway as its not rigid enough to take the deflection out of the floor

so I would go for a replacement any way

if you could remove the pva from the surface of the board you could overboard with hardy backer bedded on addy , which would bring you up to 18mm

problem is getting the addy to adhere to pva

so best bet is rip up and start again

[whitebeam]

Do you know if the pva was thinned out or put on straight from the container

[tactile]

cheers all!
i would have thought the PVA would've been 1part to 4 parts water but dont know this for sure.
i know 12mm isnt ideal but its very sturdy, the joiner nailed it every 10cm and then the original tiler put screws inbetween every nail!!! . . This is the reason i'm asking the question, cos its gonna be a bugger to take up! Would Bal primer not seal the pva?

or would all them nails and screws weaken the wood as apposed to making it sturdy?

confused?

[whitebeam]

I'd try some warm water on the ply and see if you can scrape off any pva, sbr thinned to a 3-1 would be what I would be using to prime the ply.

Or perhaps as already mentioned 6mm hardie backer

[Alan.P]

Take up all the tiles, scape / sand / wash off the pva, the underside and edges of the ply should have been primed with an sbr primer and then, depending on adhesive, depends on the primer, as said, 12mm is on the thin side, have you got height issues, can you overboard for piece of mind ?

[tactile]

yeah! i think the Hardibacker is the easiest option, but pricey for 25mtr!

i'll screw it down with adhesive under it for good measure!

cheers everyone!

[doug boardley]

12mm is insufficiant for overboarding anyway as its not rigid enough to take the deflection out of the floor

so I would go for a replacement any way

if you could remove the pva from the surface of the board you could overboard with hardy backer bedded on addy , which would bring you up to 18mm

problem is getting the addy to adhere to pva

so best bet is rip up and start again

the hardie backer doesn't make the sub floor more rigid tho' Mike, it needs to be a minimum of 18mm wbp ply, then I'd suggest hardie on top of that

[Scott]

Why is the a need to seal the underside of the boards? Isnt that just overkill?

[doug boardley]

Why is the a need to seal the underside of the boards? Isnt that just overkill?

No Scottley, it prevents moisture ingress penetrating the laminated layers of ply and thus debonding, the edges should be sealed too