Joist - ? - Tiles

[tackit]

Bathroom project.

All old floor boards removed and joists exposed, so my question is what do I put down before laying porcelain tiles?

I know the adhesive wants to be cement based flexi but am unsure of the substrate to use.

Will 12mm cement based boards be sufficient to tile over on their own?

 

[Burnerman]

Personally I'd go for 18mm OSB.....12mm cement boards are much too weak.
John

 

[AdamCH]

You can't fix 12mm tile backer directly to the joist, it's nowhere near strong enough - you'll be straight through it.

I'd recommend:

Use exterior grade ply - minimum 18mm but 22mm is better. Depends on how far spaced your joists are though. Use lots of noggins to help strengthen the floor and support the ply. Screw it to the joists and noggins - I fix every 4 inches but that's probably more than necessary.

Then overboard with 6mm hardie backer board / other tile backer board. If you are going to under floor heat then use an insulated backer like Marmox.

For adhesive use a rapid set single part flexible like Weber set Rapid SPF. Use white if the tiles are light coloured and grey if they're dark.

 

[tackit]

Ok thanks very much. I did ask at the builders merchants and they came up with the same.