tiling over floorboards

[Chrissy78]

i know that this subject has been covered loads but i cant find anything that asnswers my specific question.

i want to tile the entire ground floor in ceramic tiles and all but the living room is concrete based. there is quite a lot of play in the floorboards in the living room so i realise that i need to put some plywood down to strengthen it. but, can i just totally replace the existing floorboards with 12mm ply fixed to the joists or does it definately need to be overlayed?
the reason being that i don't want to raise one room higher than the other rooms as this will make the whole project pointless (making a clear continuous and matching run).

will just 12mm plywood be ok to tile over and what preparations should i use.

thanks
Chrissy

 

[WoodYouLike]

You have to use 18mm plywood at least, 12mm is not loadbearing and will flex.

 

[Richard C]

there is quite a lot of play in the floorboards in the living room so i realise that i need to put some plywood down to strengthen it. but, can i just totally replace the existing floorboards with 12mm ply fixed to the joists or does it definately need to be overlayed?

The tile base must have no perceivable flex or your tiles will fail & the reasons for the floorboards moving must be sorted out first. The minimum recommended overboard is 15mm WBP ply; 12mm WBP overboard is sufficient in most cases on suspended floors in bathrooms, but that’s the minimum. A ground floor is, however, more heavily loaded & 12mm overboard may not be sufficient. You cannot just lay 12mm onto the joists, it will not give sufficient rigidity & the tiles will fail. I would only use 25mm for a heavily loaded/used suspended ground floor. You will need a decoupling membrane between the concrete floor & the timber or it will crack where they meet.

the reason being that i don't want to raise one room higher than the other rooms as this will make the whole project pointless (making a clear continuous and matching run).

One way around it is to raise the concrete floor to match the new timber floor

will just 12mm plywood be ok to tile over and what preparations should i use.

No, it WILL fail; as I said above I would use 25mm.

Have a tread of a very recent & very similar thread;
//www.diynot.com/forums/viewtopic.php?t=208810