Bathroom wet UFH floor buildup

[Super_Paulie]

On 15/02/2026 at 23:51, Nickfromwales said:

I've never used backer board and only ever 6mm or more of plywood (glued and screwed down) and then tile straight onto the ply.

 

I've bought this from Wickes before I even clicked on I should have got marine ply. 

 

Wickes 6mm ply

 

Will this stuff be ok? I'll be tiling, so priming and flexible adhesive on top of this.

[Nickfromwales]

39 minutes ago, Super_Paulie said:

 

I've bought this from Wickes before I even clicked on I should have got marine ply. 

 

Wickes 6mm ply

 

Will this stuff be ok? I'll be tiling, so priming and flexible adhesive on top of this.

Yup. It'll stick like shit to 2 blankets  I've never bought marine ply as if the water is getting to the plywood, you're already wrapped in both of those blankets!

[Super_Paulie]

12 hours ago, Nickfromwales said:

Yup. It'll stick like shit to 2 blankets  I've never bought marine ply as if the water is getting to the plywood, you're already wrapped in both of those blankets!

 

Great, I'll crack on then. Off work for a few weeks so I'm hoping to get the bathroom somewhere near sorted. Just spent the day setting up a temporary bathroom in the neighbouring bedroom... When you gotta go you gotta go!

[Nickfromwales]

8 hours ago, Super_Paulie said:

 

Great, I'll crack on then. Off work for a few weeks so I'm hoping to get the bathroom somewhere near sorted.

Use LOTS of 4.0 x 25mm screws to fix the plywood down, and if the subfloor is even SLIGHTLY suspect I put the ply down over a 3mm notched bed of neat PVA.

[Super_Paulie]

5 hours ago, Nickfromwales said:

Use LOTS of 4.0 x 25mm screws to fix the plywood down, and if the subfloor is even SLIGHTLY suspect I put the ply down over a 3mm notched bed of neat PVA.

 

That's my plan. 25mm seems scarily close to the pipes though. I've got 20mm and 25mm screws, just to see what I dare put in. Seems 25mm is only an impact driver away from spoiling the whole party with the pipes underneath.

[Nickfromwales]

7 hours ago, Super_Paulie said:

 

That's my plan. 25mm seems scarily close to the pipes though. I've got 20mm and 25mm screws, just to see what I dare put in. Seems 25mm is only an impact driver away from spoiling the whole party with the pipes underneath.

22mm deck or 18mm deck?

 

If 22mm deck, plus 6mm ply, then you’ve got 4mm before you poke out the other side.

 

My impact drill has 4 setting for speed / torque, so is much more manageable, but if you’re not rushing you’ll be fine. 
 

I mark a grid out and go for a minimum of 120 centres, 100mm best practice imho. Never had issues so I don’t deviate from this.