possible problem floor

[negsy26]

hi guys,got a folor to tile in a few days and there is a potential problem,the floor has been ripped up and 'apparently' 12mm wbp ply has been put down. now, i do not know nor does the guy who lives there if this ply has been sealed underside or edges !! whats the best way out of this ? many thanks .

[timeless john]

First thing to establish is it 12mm plywood and what tiles do you intend putting down.
How big is the floor and what weight do you anticipate it will be.

[david campbell]

if the floor has been ripped out then 12mm ply isn't really sufficient,it should be 22/25mm and extra noggins into the joists to stabilise the floor from any movement

[negsy26]

22-25mm !! surely 18mm is the max needed !! its a bathroom so the usual bathroom traffic not sure how big as i have not seen it and been told its 333x333 ceramic tiles going down, 12mm ply should be fine or maybe overboard with 6mm backerboard but not sure about the edges and underside not being sealed having an effect in time.

[grumpygrouter]

I think David thought you meant 12mm straight onto joists, not as overboarding!

[david campbell]

when you said "the floor had been ripped up" i assumed you meant the floorboards or t&g

[negsy26]

well to be honest im not sure what the hell has gone on as ive not seen the job yet.so lets assume worst case scenario here-12mm ply straight onto joists which has not been sealed underside and edges.whats the advice on that ? many thanks you guys.

[Dan]

That's not enough, you'd stand between the joists and it will move. You need to seriously consider deflection in the floor; movement up and down with weight.

If there ARE T&G boards down, you'd still need to use a minimum of 15-18mm according to british standards. If the boards have come up, you need 22-25mm.

Don't let this whole job come back on you because of somebody else's mistake. Either advise them correctly and do the job right, or let some other shmuck do it and go back in 6 - 12 months when it's all gone wrong.

You could overboard it again perhaps, which wouldn't cost too much and shouldn't be too much of a maul. But you need to make sure that the existing boards have had extra noggins added, and for sure, the right size SCREWS (not nails).

I'd take a look at it myself if I were you.

[negsy26]

yeah thats cool dan, im looking at it tomorrow and should get some more info as builder will be there, to be honest i was more concerned about what could happen if the underside and edges have not been sealed but everything else is ok? and just out of interest do you guys prime the face of plywood prior to tiling or just seal the underside and edges? i myself have primed and havent, i was just curious !!

[whitebeam]

Thats why I like hardie backer, no priming

[negsy26]

haha right guys looked at this floor this morning. its 2msq and 300x300 travertine is going down.floorboards have been overboarded with 6mm ply(not 12mm like i was told ! ) screwed down every 200mm. having jumped around on it quite a bit i must say im impressed as it doesnt move at all.the question is tile straight on top or not? underside and edges not been sealed !

[Sir Ramic]

6mm is not adequate, you may as well tile onto cardboard. Do it right and do it once

[Dan]

I agree. If the ply is on top of T&G, 6mm isn't enough. Even for ceramics according to the british standard. So you'd need to overboard again with 12mm (to get 18 total) as it's travertine you're sticking down and not just lightweight ceramics.

I understand there will be concerns with the height, T&G + 6mm + 12mm + adhesive + travertine but imagine you having to pay to rip it all up and do it properly in 12 months time. I'd rather do it right the first time personally.

[negsy26]

how about 6mm backerboared stuckdown with flexi and screwed down? will that work as that will bring the finished level down a bit?

[timeless john]

If your happy that the floor is sound /no deviation Hardie should be fine.
Follow their instructions cover all the ply joints and tape the boards.

[negsy26]

cool, thanks guys. i told the builder next time make it 18mm ply if going on top the floor or 25mm if going on the joists.i think he has taken it onboard !!