Shower tray fitting on wood decking

[G and J]

2 hours ago, Nickfromwales said:

Ok, so you may want to go for 12mm plywood everywhere else upstairs, and drop back to 6mm at the threshold of the bathroom doorway. That'll allow you the 'good job of it' plywood layer, and then a 6mm deficit for you to install a mat and some electric heating mat, submerged in SLC (use Mapei LINK as it has fibres), and then your LVT will be flush from the hallways to the bathroom floor.

 

Everything needs priming, expect @Pocster, he's already primed to the hilt. 

 

Brush some primer / water solution over the floor and UFH immediately before mixing the SLC, as you need to lay 'wet on wet' here for success.

 

Add 1/4 pint of water to the SLC right before you throw it onto the floor, after you mix it to their instructions. 

Oh well, if I should have allowed for 12mm ply throughout upstairs then I need to add another line on the “I screwed up” list.  Ho humm.  
 

But our stairs are in and the levels are set for 9mm total floor covering depth - 6mm ply plus ~3mm of LVT.  We’ve no thresholds between rooms as we want a continuous floor treatment throughout.  So the electric matting goes onto the chipboard, with the levelling compound.  We’ve been recommended a local flooring company who are happy to apply the levelling compound on the UFH mats I install. 
 

I’ll be putting the shower trays direct onto the chipboard as I’d rather not see a line of ply under them.  Perhaps my next step is to test fit the trays and see how flat, stable and level they are, and then take it from there. 

[Nickfromwales]

1 hour ago, G and J said:

Oh well, if I should have allowed for 12mm ply throughout upstairs then I need to add another line on the “I screwed up” list.  Ho humm.  
 

Another one for the free 1hr chat I offered you, lol. You are a tough cookie to crack....aka stubborn.  Same here.

[Nickfromwales]

9 hours ago, G and J said:

Oh well, if I should have allowed for 12mm ply throughout upstairs then I need to add another line on the “I screwed up” list.  Ho humm.  
 

But our stairs are in and the levels are set for 9mm total floor covering depth - 6mm ply plus ~3mm of LVT.  We’ve no thresholds between rooms as we want a continuous floor treatment throughout.  So the electric matting goes onto the chipboard, with the levelling compound.  We’ve been recommended a local flooring company who are happy to apply the levelling compound on the UFH mats I install. 
 

I’ll be putting the shower trays direct onto the chipboard as I’d rather not see a line of ply under them.  Perhaps my next step is to test fit the trays and see how flat, stable and level they are, and then take it from there. 

You won’t see the ply as the rest of the floor covering comes up way higher than that.

 

You’re very brave putting SLC straight down onto the chipboard, but if someone says they’ll warranty the job without even a 3.6mm (aka 4mm) ply binder then it’s on their head I guess.

 

I’ve never laid anything directly onto particle boards, ever, but I have had lots of insurance work from others who did so.

[Super_Paulie]

On 01/03/2026 at 13:53, Nickfromwales said:

https://www.protilertools.co.uk/product/ultra-tile-fix-proprimer-advanced-polymer-primer?msclkid=9ae67650c99f1ca414e81ff48b4305ea&utm_source=bing&utm_medium=cpc&utm_campaign=Shopping%3A Pro Tiler Tools&utm_term=4585925567009231&utm_content=1.1 All Products - Pro Tiler Tools

 

Most tile places will sell this or similar.

 

Use it neat on the underside of the try, it may take a lot, and then on the floor dilute by 25% with water and get the deck sopping wet. Leave for 15 mins for the surface to saturate, then buff back off any excess with a sponge or tea-towel etc.

 

Does this still l hold true for tiling @Nickfromwales? I'm going for porcelain over 6mm plywood (which is over chipboard) already glued and screwed. I went over it with Ultra primer 3:1 mix last night, should I go over over it again just before I start to mix up my adhesive? Instructions on the container are ropey at best. Advice welcome.

[Nickfromwales]

2 hours ago, Super_Paulie said:

 

Does this still l hold true for tiling @Nickfromwales? I'm going for porcelain over 6mm plywood (which is over chipboard) already glued and screwed. I went over it with Ultra primer 3:1 mix last night, should I go over over it again just before I start to mix up my adhesive? Instructions on the container are ropey at best. Advice welcome.

If it's a solid deck then you'll be good to just have a damp sponge in the dilute mix, and use that 1m2 at a time as you're laying, just to stop the surface from being 'dry' when the tile adhesive hits it.

[Super_Paulie]

37 minutes ago, Nickfromwales said:

If it's a solid deck then you'll be good to just have a damp sponge in the dilute mix, and use that 1m2 at a time as you're laying, just to stop the surface from being 'dry' when the tile adhesive hits it.

 

Gotcha, it's solid as in 22mm P5 with 6mm Ply glued and screwed. It says on the back of the container that it must be dry before adhesive, which is kinda the opposite to what I've read on here where it needs to be "tacky". I've just found a tech sheet from UltraTile SPES that says to apply it neat on plywood before adhesive as well, so that's 3 options! 🤣

 

Happy to go with professional plumber experience with this one though 👑 

[Oz07]

10 hours ago, Super_Paulie said:

 

Gotcha, it's solid as in 22mm P5 with 6mm Ply glued and screwed. It says on the back of the container that it must be dry before adhesive, which is kinda the opposite to what I've read on here where it needs to be "tacky". I've just found a tech sheet from UltraTile SPES that says to apply it neat on plywood before adhesive as well, so that's 3 options! 🤣

 

Happy to go with professional plumber experience with this one though 👑 

Ive not read the whole thread but is there a reason you overboarded with ply? I thought p5 was good stuff. 

[Super_Paulie]

2 hours ago, Oz07 said:

Ive not read the whole thread but is there a reason you overboarded with ply? I thought p5 was good stuff.

the chipboard is there purely to act as a backer for the tiles, ive been informed tiling directly onto P5 is not a good idea.

[marshian]

11 hours ago, Super_Paulie said:

the chipboard is there purely to act as a backer for the tiles, ive been informed tiling directly onto P5 is not a good idea.

 

Rightly or wrongly before tiling I've always over-boarded chipboard floors with 5 or 6mm ply and then stapled it down (rather than glue or screw) then tiled over the top of the ply. My logic was if I ever need to replace the tiles it was easier to get the tiles off then the 5 or 6mm ply up with the adhesive to get back to a nice clean and level surface - re-board and again and re-tile.

 

I get to test my plan shortly as both Utility and Kitchen floors need re-tiling!!!

 

The Kitchen floor needs replacing fully replacing due to a water leak that got under the floor tiles 😞

 

[Super_Paulie]

10 minutes ago, marshian said:

 

Rightly or wrongly before tiling I've always over-boarded chipboard floors with 5 or 6mm ply and then stapled it down (rather than glue or screw) then tiled over the top of the ply. My logic was if I ever need to replace the tiles it was easier to get the tiles off then the 5 or 6mm ply up with the adhesive to get back to a nice clean and level surface - re-board and again and re-tile.

 

I get to test my plan shortly as both Utility and Kitchen floors need re-tiling!!!

 

The Kitchen floor needs replacing fully replacing due to a water leak that got under the floor tiles 😞

 

 

I full bed PVAd the ply, no chance that would ever come up!