Advice for Wetroom Floor

[SimpleSimon]

Hi there

I'm a DIYer putting in an upstairs wetroom floor. I'm currently at the stage of floor joists, which I've beefed up with extra noggins so it's good and solid.

Does the following list of layers make sense? Is it overkill (or underkill!)? All comments very much appreciated!

1. 18mm WPB ply (not marine ply)
2. 6mm tile backer board
3. Tanking primer (from wetrooms-online)
4. Tanking solution and tape on joints (again from wetrooms online)
5. Tanking solution layer on everything
6. Electric underfloor heat mat
7. Tile adhesive
8. 8mm Slate Floor Tiles
9. Grout
10. Slate Tile sealing solution

I'm using a wetroom tray (yet again from wetrooms online) in the shower itself, so this will replace the tile backer board in step 2.

I know some people have concerns about slate in bathrooms but its a gamble which "we" (as in my wife) have decided to take.

Thanks for your help
Simon

 

[Simon Dale]

10mm backer 6a decoupling

 

[SimpleSimon]

Thanks for the quick reply Simon!

So I add 10mm backer on top of the heat mat before laying the adhesive. Does this mean I can remove the 6mm backer in step 2 or do I need both?

(I'm not concerned about heat going downwards as its a warm kitchen below and there will be mineral wool insulation between the joist to reduce sound transmission anyway.)

 

[Old Mod]

I think what Simon is saying is
10mm backer over ply, and a decoupler over ufh mat because you’re using a natural stone product.
We would never suggest laying stone without a decoupler or antifracture mat, with or without ufh.

 

[Old Mod]

Personally my approach would be slightly different.
10mm backer over ply, or 6mm hardie if height really is a big issue. Joints taped
Then ufh mat.
Latex over ufh mat, not only to protect it but to give a good uniform surface to tile to and to deliver better heat transfer.
Then I would tank everything before laying tiles.
To my thinking, why would you tank below an electrical system that runs the risk of getting wet?
Surely you’d want the electrical element of your floor protected at all costs?
Well I would anyway.

 

[SimpleSimon]

Edit: Crossed posts - posted this before reading 3_fall's second post so deleted and will repost

 

[Old Mod]

Close 🙂
I would put the ufh under tanking,
And latex over cables before tanking, for reasons explained above.

 

[SimpleSimon]

Thanks 3_fall - that makes sense what you said about the electrics - sorry for the crossed posts!

So my new list is like this?

1. 18mm WPB ply (not marine ply)
2. 12mm tile backer board (I can only get 12mm rather than 10mm)
2a. Electric underfloor heat mat
2b. Latex
3. Tanking primer (from wetrooms-online)
4. Tanking solution and tape on joints (again from wetrooms online)
5. Tanking solution layer on everything
6a. Decoupling mat
7. Tile adhesive
8. 8mm Slate Floor Tiles
9. Grout
10. Slate Tile sealing solution

 

[Old Mod]

That’s about as belt and braces you could get.

But..... 😀

Actually after engaging my brain properly, not something that’s done often on a Sunday.

After latexing over your ufh you can use a waterproof antifracture mat instead of the other two processes,
Sorry, I should of been more focused when replying.

So......,
Backer boards over ply
Ufh
Latex
Waterproof antifracture mate
Tiled
Done

 

[Old Mod]

Green waterproof antifracture matting over ufh

Ready to be tiled