9mm marine ply

[jivemonkey]

Hi,

Bought 9mm marine ply, cut to size as one piece, to lay onto first floor level bathroom floorboards then overlay 6mm hardibacker boards with adhesive and screws into the ply.

I have been told 9mm ply is too thin and my tiles will crack (they are large rectangualr tiles), but is this the case when there are already floorboards and I will also overlay hardibacker, should I buy a thicker piece around 15mm to be on the safe side??

 

[RDTiling]

Hi there.

If your floor boards are free from deflection, then you can miss out the ply wood completely and put hardi backer board straight onto the floor boards and then you are good to start tiling

hardie boards should be 'glued and screwed' to the floor boards and by that I mean trowel tile adhesive (6mm trowel) over the floorboards and then set the hardi boards of top of the adhesive and them screw the boards down.

hardie recommend that a non-flexible adhesive is used to fix their boards, however I know of plenty people who use flexible adhesive and have never had and problems.

Also, the joints between the boards should be taped as per hardie's instructions.

I hope this helps.
Rich

 

[Qwerty]

http://www.jameshardie.co.uk/images...ent_backerboard_installation_guide_manual.pdf

 

[RDTiling]

http://www.jameshardie.co.uk/images...ent_backerboard_installation_guide_manual.pdf

The short version of my reply, I should've thought of that!

 

[beanz]

As above, it's all about the deflection. If there's no bounce in the floor, you're good to go. Otherwise, I'd use at least 12mm, although British Standards quote 15mm. Make sure your floorboards are all solid, and screwed down before you start. If you're going down the ply route, you could over lay that with Ditra matting, rather than Hardy, so you'll get 3mm back.

 

[thompsonbrown]

Hi,

Bought 9mm marine ply, cut to size as one piece, to lay onto first floor level bathroom floorboards then overlay 6mm hardibacker boards with adhesive and screws into the ply.

I have been told 9mm ply is too thin and my tiles will crack (they are large rectangualr tiles), but is this the case when there are already floorboards and I will also overlay hardibacker, should I buy a thicker piece around 15mm to be on the safe side??

If your floor is pretty sound and free from deflection you probably would get away with just Hardy. If you start looking at overboarding with say 15mm ply, then hardy then tile. You end up with a huge step into the room.
If the floorboards are in bad shape why not rip them up put a few extra noggings in where needed and lay a new floor using 18mm ply. Its a bit more work but it will look better than a step.

 

[White Room]

All to the above...

 

[jivemonkey]

thanks, the floorboards dont seem to move much, not noticable anyway, previous floor was mosaic on thinner ply and that was okay my idea was 9mm ply then 6mm hardibacker screwed and adhesive down = 15mm sub tile flooring to give a stiff floor but I am leaning towards buying 15mm ply as I would rather over engineer than end up having to refit my floor which would be a horrendous amount of work...