Tiling over floorboards in bathroom

[J_c]

Hi -- I'm a competent DIYer but new to tiling and looking for a little advice. I'm renovating the bathroom at my new place as when I moved in it was in a horrid state -- water damage everywhere, blown plaster, leaky soil pipe etc. I've ripped out everything back to the bare floorboards and capped all pipes; now I'm looking to tile the floor so I can install a new bath, sinks, loo etc.

My question is about how to tile a suspended timber floor. It's square edged rather than t&g, if that's important, and it's generally in good nick but a bit uneven and damaged in places, and I understand that the natural movement in timber floors causes serious problems for tiles. Would the best thing to do be to remove it and replace with 22mm plywood, then add a waterproof backing board over that before tiling? Or should I leave the floorboards in place and put plywood then backing over them?

Any advice would be very welcome; I'd also be grateful if you could offer any tips or direct me to a step-by-step guide to this kind of flooring. I'm generally good at this sort of thing but, as I say, I'm new to it and looking to do a good job.

Thanks for running such a helpful forum! Jim

 

[Andy Allen]

As you have taken everything out I would remove the floor boards, add some extra noggins between the joists to reduce any deflection, board the floor with 22 mm ply but prime the underside an edges of the ply first, then fix some 6mm cement board to the surface of the ply, fix it with adhesive and screws, this will give you the perfect surface to tile too...!

 

[J_c]

Lovely, thank you! Would hardie backer be the normal choice for 6mm cement board? And while I have you -- what would you recommend I use to prime the underside and edges of the ply?

 

[Qwerty]

Use an SBR or acrylic primer. @HardieBacker is a popular choice for overboarding and will be perfect for your needs

 

[J_c]

Excellent, cheers. And a dumb question -- when Andy says prime the underside of the plywood, is that the side that contacts the joists or the side that contacts the hardiebacker?

If it all turns out ok, I'll get back to this thread with photos and let you know how it turned out ----

 

[Qwerty]

All over, underside, topside and sides

Yes, please do share with us all afterwards