Subfloor advice for tiling

[DIY Bobster]

I am looking for some advice on suitable bathroom subfloors on joists. I have had a look on the forum, and am struggling to find an answer.

Currently the bathroom subfloor is some kind of 18mm chipboard screwed onto the joists (400mm centres). Previously carpet was laid on top of this so deflection of the sub floor wasn't a worry. The bathroom is relatively small (tiled area is approx. 1.2m x 2m). I am planning on adding electric under floor heating and then tiling. An additional consideration is that I can't go too high with the floor height, so adding a layer of cement backer board onto chipboard and then adding Wedi layer wouldn't work.

Previous advice from a bathroom fitter was to keep the existing subfloor, add 6mm Wedi board to act as insulating layer for the electric UFH and then tile on top of that. However, when searching to see if any bonding was required between chipboard subfloor and Wedi (other than screws), I cam across lots of advice against tiling onto chipboard as the subfloor.

Additionally, the current subfloor resembles swiss cheese due to me and my multitool making some exploratory holes to see what the joist were like and pipes etc. SO I am now thinking the best way would be to rip up the chip board and start again onto joists.

What options do I have for starting from scratch or (if possible) keeping the existing subfloor?

Thanks in advance!

 

[drives]

We had a similar dilemma but similarly we didn't want to raise the overall finished height of the floor. Have you considered glue down lvt with design strips to mimic tiles? Done well, it can look good. That might negate the desire for electric UFH which is presumably to combat the cold tile underfoot. Realistically how likely are you to use UFH in one room? We've had it in a previous house in an en suite and never turned it on.

 

[tell80]

OP,
Presumably, you now know where (if any) your pipe & cable runs are in the floor?
The 18mm chipboard must be firmly screwed down to the joists and no movement present.
A few holes in the c/board are irrelevant.
Then glue/screw down the backer board to the joists thro the chipboard.
As above, forget about elec UFH.