best products to use over joists before tiling ?

[bmx]

Hi i have stripped a bathroom floor that was rotten and wanted to know the best way to re board it as i plan on tiling the floor?

the joist centres are 450 and a few are at 400.

is there a product like cement partial board that will do the job in one? or do i need to use 18mm ply then the hardie stuff?

 

[Paul C.]

You'll need to board the floor out first with moisture resistant chipboard (the green stuff) or 18mm WPB Ply. Overboard that with the 6mm hardie backer or a further layer of 18mm ply. Whichever you go for, the overboard will need to be screwed down at 300mm centres (this is the recommendation from British Standards BS5385), and that should be good to go. But as it is a new substrate and it will take time to settle, I would seriously consider using a decoupling membrane to cater for lateral movement.

Any Ply or chipboard, would need to be sealed with an SBR Primer on the back and sides to prevent distortion from atmospheric change.

In your situation, over boarding is a MUST. your joists are too far apart so there would be too much deflection regardless of the board type or thickness you choose.

 

[bmx]

ok thanks is there a way of doing it so i can just tile onto the floorboard, i.e. if i pt an extra joist in between every joist to make the centres 225 ish and use flexible adhesive onto a new green chipboard floor ??

 

[ree]

There's no need for any extra joists: 400mm is 16" the traditional spacing for centres. 450mm is neither here nor there - no deflection will take place.
Neither are two layers of 18mm necessary - we've often laid tile on 22mm T&G floor boards or ply, using flexi adhesive and flexi grout. Not recommended but it works.
Green T&G chipboard is fine but any kind of WPB is an unecessary expense.

18mm with 6mm backer board will work fine - nothing else needed.