To tile on 18mm ply or?

[Jim85]

Hi, first post and a beginner to tiling (first job as a favor to parents!). The job is a small bathroom ( 5 x 8 ft ), original subfloor was rotten/warped chipboard that had been soaking over a period of 5+ years from a leaking bath seal. Pulled it all up and put down 18mm ply over joists with a dozen noggins glued and screwed in to take out as much deflection as possible. The floor is now solid and am wondering what would be the next step in preparing the surface before tiling.

Undersides and edges were primed with an acrylic primer.
The joins in the plywood are all supported by joists/noggins and all bar one join in the ply is perfectly flush. The one join has a lip of about 1 -2 mil.
Tiles have already been bought and are 280 x 360 johnson ceramics.

I've read countless posts and information about covering the ply with ditra, durabase, 6mm hardibacker and just tiling straight over the ply, but can't decide what would be the best option. I was thinking of thinsetting durabase over the ply to both get rid of the lip and provide a good tiling substrate at the same time (I believe this method would add the least depth to the current floor level as ideally that would be kept to a minimum). My questions regarding this method is with the thinset choice.

Would I have to prime/seal the top of the ply?
Would I use modified/unmodified thinset to lay the durabase?
Would I then use a waterproof flexi bagged adhesive on top of that? I've seen vids/posts showing tiles being bed in a further layer of thinset on top of the matting.

Any direction would be much appreciated as a bit lost in the options that seem to be available to me right now

Cheers

Jim

 

[Ian]

Welcome along to TF. If I were in your position, I'd stick 6mm hardiebacker to the ply and screw it also. Then tile with SPF. Whichever adhesive you choose will determine whether you prime the ply or not. Just follow the manufacturers instructions. The ditra/durabase is not needed IMO.

 

[Jim85]

Thanks for the quick reply mate, yeah it seems the more straightforward of options for sure. You say stick and screw, i'm guessing with a normal thinset? The only bother I have with throwing down hardi is getting the door to still fit inside the lining after the hardi/addy/tile depth. That and hoping it's not as hard to cut as the 12 mil stuff. Cheers

 

[Ian]

It's not as hard to cut as the 12mm. Hardie recommend that it is stuck down with a non-flexible adhesive, make sue you screw it down while the adhesive is still wet and that you use alkali resistant tape on the board joints. I did a fitting guide a while back, I'll find it and post a link.

 

[Ian]

http://www.tilersforums.com/tiling-forum/58805-installation-hardiebacker-250-500-a.html