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

 

[Simon Dale]

Isomat ??

 

[Simon Dale]

You got that one in before me lol

 

[Old Mod]

Isomat ??

Yes Simon.

 

[WetSaw]

You can get some very realistic looking slate effect porcelain tiles just to confuse things a bit more!

 

[SimpleSimon]

pdc: I already have the slate tiles, so that's one thing I don't have to think through!

3_fall and Simon: So something like this for the waterproof anti-fracture mat (I can search through the forum to get particular brands):

Decoupling / Anti-Crack Membrane - http://www.thewetroomstore.co.uk/decoupling-anti-crack-membrane/

And I can just tape together rather than using any liquid tanking at all, then tile straight on top?

 

[Old Mod]

Yes you can Simon.
I’d be interested to know who makes their one, there are very few that are waterproof.

 

[Old Mod]

Our sponsor Isomat (logo top of page above) supplies the green one in my images.

 

[SimpleSimon]

Sounds like that's the one to use then, assuming I can get someone to ship it to Dublin, but that's another thread altogether...

Just to be 100% sure I've got it, here's my new list:

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
6a. Isomat or similar, taped on seams and at walls
7. Tile adhesive
8. 8mm Slate Floor Tiles
9. Grout
10. Slate Tile sealing solution

 

[Old Mod]

Thats exactly right.
For me anyway.

 

[SimpleSimon]

Perfect - thanks to you and the others for all your help

 

[WetSaw]

Doesn't the slate want sealing before grouting?

 

[Simon Dale]

Usually I find slate is very dirty so needs to be washed and completely dry before sealing, or take care with grout and adhesive seal when finished must be dry or picture framing !!

 

[SimpleSimon]

Thanks for the extra tips - now you mention it, the sales people did suggest sealing the slates both before and after laying, so I'll do that, and also wash & dry them first.

A couple of other questions while I've your attention too...

What's meant by the latex layer that goes on the UFH? Is this a powdered tile adhesive that's been enriched with a latex solution like this one, or something else?
Everbuild Floor Flex Plus Latex Leveller Liquid 5 Litre - https://www.goodwins.ie/products/everbuild-floor-flex-plus-latex-leveller-liquid-5-litre-0071025.html

Also, I've a couple of options regarding tile backing boards. There seem to be two types - cement boards like Hardibacker or this one here:
Permabase 8x4' 12mm Non Combustible Cement Board - https://www.goodwins.ie/products/permabase-8x4-12mm-non-combustible-cement-board-0023296.html

Or foam based ones like this one:
12mm Tile Backer Board 1.2 x 0.6mtr - https://www.goodwins.ie/products/12mm-tile-backer-board-1-2-x-0-6mtr-0023293.html

I'm guessing I'm better off with a cement board for a floor?

Sorry for all the questions!

 

[WetSaw]

Latex otherwise known as Self Levelling Compound.

 

[SimpleSimon]

OK, thanks pdc, I've used self levelling compound before - it wasn't very self levelling as I recall!