Shower tray fitting on wood decking

[G and J]

I’m having a couple of hours off the build, so of course I’m on here researching.   No hope is there.  

 

We have 22mm decking (a caberboard equivalent) upstairs throughout.  I believe it’s really nice and flat but I will check that carefully.  I’ve read up all I could find on here, and as a result I think …..

 

I don’t need to fetch up the flooring to replace with marine ply, but I do need to prime it.  I think this is for adhesion rather than waterproofing.  

 

The tray instructions say lay on a bed of sand and cement, but if the decking is flat then ct1 appears an excellent bedding material.  I can’t believe the mortar mix won’t just turn to dust over time, with footfall and temperature cycling (J has skin removing shower flow temperatures!). 

 

We’ve put 15mm green plasterboard with oodles of screws on max 400mm centres, and we can tank that after fitting the shower tray.  If it’s better or easier or both to do beforehand please correct me. 

 

The wastes are lurking in holes in the floor, all connected up and ready, they sit quivering with anticipation on their own special noggin so they can’t drop too low.  When I actually fit them to the tray I’ll put a wipe of ct1 on the trap itself under the rubber washer, then on the washer, before carefully not cross threading the top bit as I screw it in.   I’ve practised that a couple of times using a 12mm plywood stand in shower tray with a 90mm hole in it.   I really must get out more. 

 

Then I scrubby scrub the shower tray’s bottom, (a clean bottom always helps) before carefully squirting ct1 on the bottom of the tray before dumping it in place.  I then pull it away from the walls a bit and squirt yet more ct1 into the gap before pushing it home.  

 

Next day I run water into the tray and watch underneath for drips or expanding wet patches on my ceilings.  Simples.  

 

So what can I improve on all that?

Edited February 21 by G and J
Guess who pressed return too early!

[Oz07]

Has anyone ever bedded one in on foam?

[MikeGrahamT21]

I’ve heard people using flexible tile adhesive in place of sand and cement, seems a good strong option which will flex with heat cycles and loading

[G and J]

52 minutes ago, Oz07 said:

Has anyone ever bedded one in on foam?

That would scare me.  Partly as I hate foam. 

[G and J]

47 minutes ago, MikeGrahamT21 said:

I’ve heard people using flexible tile adhesive in place of sand and cement, seems a good strong option which will flex with heat cycles and loading

There’s a good few posts advocating that too, and I guess from my point of view both will give a good, strong bond with enough flexibility to endure.  I’ve got ct1 and I’ve used it many times so I’m at home with it, hence my preference.  But I’m open to other viewpoints. 

[Nickfromwales]

57 minutes ago, Oz07 said:

Has anyone ever bedded one in on foam?

Nobody sane!

[Nickfromwales]

10 minutes ago, G and J said:

There’s a good few posts advocating that too, and I guess from my point of view both will give a good, strong bond with enough flexibility to endure.  I’ve got ct1 and I’ve used it many times so I’m at home with it, hence my preference.  But I’m open to other viewpoints. 

Is it a stone-resin tray?

 

If so, use flexible tile adhesive, it takes much better to the tray, and as you say using said mixture to scrub and key the underside so get a great bond.

 

2 hours ago, G and J said:

The tray instructions say lay on a bed of sand and cement, but if the decking is flat then ct1 appears an excellent bedding material.  I can’t believe the mortar mix won’t just turn to dust over time, with footfall and temperature cycling (J has skin removing shower flow temperatures!). 

Same here. Every one I've taken up to replace has turned to crumbs.

 

2 hours ago, G and J said:

we can tank that after fitting the shower tray.  If it’s better or easier or both to do beforehand please correct me. 

Do as much tanking as you can before fitting, so you don't get it over the new tray. It's best to leave that cure and CT1 the tray to tanking, and then just cut in a final coat after you've fitted the tray. Lots of thin layers and make sure it has dried before fitting the tray.

[G and J]

8 minutes ago, Nickfromwales said:

Is it a stone-resin tray?

 

If so, use flexible tile adhesive, it takes much better to the tray, and as you say using said mixture to scrub and key the underside so get a great bond.

They are, so will do.  Maybe bulk buying 38 tubes of ct1 wasn’t such a good idea….

 

9 minutes ago, Nickfromwales said:

Do as much tanking as you can before fitting, so you don't get it over the new tray. It's best to leave that cure and CT1 the tray to tanking, and then just cut in a final coat after you've fitted the tray. Lots of thin layers and make sure it has dried before fitting the tray.

Gotcha.  Makes perfect sense.  

[Nickfromwales]

2 minutes ago, G and J said:

Maybe bulk buying 38 tubes of ct1 wasn’t such a good idea….

🤐

[G and J]

6 minutes ago, Nickfromwales said:

🤐

For sale, one carefully owner…..    lol

[crispy_wafer]

I think you’re pretty well covered with advice, but I’d second getting as much tanking done beforehand, for what it’s worth I also covered the floor, any joints that were under the tray too, and all round the keyhole for the waste.  Flexible tile adhesive was also used.  
 

oh, have an old towel, some wipes nearby, and someone nearby to help wipe down cos tile adhesive sticks like sh*t and gets everywhere you don’t want it too 😂.

[G and J]

53 minutes ago, crispy_wafer said:

tile adhesive sticks like sh*t and gets everywhere you don’t want it too 😂.

I knew there was a reason I wanted to use ct1 lol

[Nickfromwales]

5 minutes ago, G and J said:

I knew there was a reason I wanted to use ct1 lol

Bucket of water and a sponge, is all you need. Wash your hands and tools frequently, but if you've done the job properly you should not see any tile adhesive after fitting the tray, whatsoever. It should all be under the tray only, so if it's looking like it's going to ooze out everywhere, you mixed too much up!!

 

Remember you do not put tile adhesive under the lip that runs around the tray underside, the adhesive stays away from those so they can move / flex, you just silicone these gaps later on.

[G and J]

Thank you NFW.  
 

However, I must flag how much I hate that word.  Just.   Sigh. 

[Nickfromwales]

3 minutes ago, G and J said:

Thank you NFW.  
 

However, I must flag how much I hate that word.  Just.   Sigh. 

"Simply" any better?

 

Just........an alternative suggestion lol. Just saying.

[G and J]

It’s the endless ‘just’ jobs that trash hours each day. 
 

It’s the face in your hands frustration of struggling with an awkward task and being asked by those watching  ‘why can’t you just?’

 

I’ve decided to classify ‘just’ as a swear word.  It can join ‘should’ on the banned list. 

[SiBee]

I have just installed our Mira stone resin tray (900 x 1700) installation  methods vary manufacturer to manufacturer. Mira recommends bed on a weak sand and cement mix or use a suitable construction adhesive. Their tech help confirmed CT1 would be suitable. I tried the sand/cement mix but wasn’t happy so cleaned it up and redone using a few tubes of clear CT1. Took a leap of faith with the level because once laid in position I could not prize it up off the adhesive. I had lowered with banding straps which snapped when I tried the lift. Left 24hrs and all solid and level.

Check out what Rodger says on the skill builder YouTube channel. 

I preferred the clear CT1 for this task. Thought process being that it’s a bit thicker in consistency than the white and the bed needed to make up a 3mm gap.

our previous tray which I installed approx 10 years ago was bedded on the sand and cement mix which was good for years but then developed creaking noises but no obvious movement? On removal,the bedding mix was all cracked and turning to dust.

I read everything the Welsh Wizard posts, he is amazing but do check out skill builder. Mira also told me not to use tile adhesive. You don’t want to bond the tray in position. Even flexi tile adhesive won’t allow for the different expansion movements.

The indecision is a painful. 
You already have a suitable adhesive if that helps. How much of a bed do you need to make up under the tray?

[Nickfromwales]

Many ways to skin a cat, but tried and tested for 3 decades wins for me.

 

If you're saying you stuck it down and couldn't then adjust or manipulate it, and hoped it was level, then I guess that's one reason not to use a sealant / mastic. I found this out a long time ago, where the mastic turns into a sucker cup and then it's a case of getting wood chisels or small pry bars under the edge to try and adjust it.

 

This was with a Novellini tray, prob 15+ years ago or more, and it was clean and spotless when laid but I did notice some bounce in the centre of it, where it was thinnest at the trap, and that was it for me. Back to tile adhesive, and never looked back.

 

9 hours ago, SiBee said:

Mira also told me not to use tile adhesive.

 

Fitted 2x Mira Flight trays on a previous build, and the client commented on how solid they felt; one on the raft slab but one also on the 1st floor deck over posi's.

 

10 hours ago, SiBee said:

You don’t want to bond the tray in position.

 

I couldn't disagree more. Such a bond is also formed when you seal the sides of the trays to the walls, 2 or 3 sides around, and fixing trays into place firmly is of paramount importance so you don't get movement / cracks in the grout where the tiles come down to meet the tray.

 

9 hours ago, SiBee said:

Even flexi tile adhesive won’t allow for the different expansion movements.

 

This is exactly what flexible tile adhesive does, the clue is in the name . The thing most people don't do is decontaminate the underside of the tray, which is often dusty and feck or has mould release agents on it. Regarding movement, these don't typically move much, if anything at all. There's a brief change in state when you turn the hot shower on, but that's about it. Even my 800x1800mm bath is stood in every day, and the grout line and silicone seal haven't shown signs of movement in a busy house with 6 people in it; I fixed a batten to the wall and set the bath down into CT1 and the same back to the 2 plaster boarded walls. Been in for around 8-10 years now with zero signs of movement.

 

Give old Skill-boy my number, and we'll go argue it out over some beers.

[G and J]

I love this forum.  Informative and interesting.  Our build is very definitely all the better for our membership.

 

Our bath and two shower trays arrive Tuesday, and I want to fit them el pronto so my next quandary is exactly what I prime the caberdeck equivalent (other brands are available lol) with and which flexible tile adhesive I use. 
 

I know I should know this stuff, but hey, throughout the rest of the build I’ve not known what I needed to know, so it’s business as usual at this end.   
 

So folks, what’s your favourite primer and sticky for this application?

[G and J]

Now don’t all rush in at once lol

[Nickfromwales]

3 minutes ago, G and J said:

Now don’t all rush in at once lol

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.

 

Don't let it dry completely before sticking the tray down, tacky at most. Butter the floor, butter the underside of the tray, and then apply a notched bed to the buttered floor, and away to go. Aim for a consistency like clotted cream.

 

What's the make up of the rest of the bathroom floor around the tray? Plywood and tiles? UFH mat to go in? Best result would be if you glue and screw 6mm plywood down onto the entire floor area, and then stick the tray down on that. 

 

Is it exposed particle board (caber) or Egger? If Egger (laminated) then you'll defo need to ply first. 

[G and J]

4 hours ago, 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.

 

Don't let it dry completely before sticking the tray down, tacky at most. Butter the floor, butter the underside of the tray, and then apply a notched bed to the buttered floor, and away to go. Aim for a consistency like clotted cream.

 

What's the make up of the rest of the bathroom floor around the tray? Plywood and tiles? UFH mat to go in? Best result would be if you glue and screw 6mm plywood down onto the entire floor area, and then stick the tray down on that. 

 

Is it exposed particle board (caber) or Egger? If Egger (laminated) then you'll defo need to ply first. 

Thank you Nick.

 

Upstairs is Kronospan Fast Clean chipboard.  The majority of upstairs will have 6mm ply with posh lino bits glued on.  In the main bathroom we will instead have an electric UFH mat thingy with a layer of levelling goo, then the posh lino bits.   The UFH mat will not extend under the shower tray, I had assumed it would just sit with the lino butting up against it, but there’s no reason I can’t screw down a layer of 6mm ply if it’s a good idea.  I assume the ply still needs priming.

[-rick-]

16 minutes ago, G and J said:

Upstairs is Kronospan Fast Clean chipboard.  The majority of upstairs will have 6mm ply with posh lino bits glued on.  In the main bathroom we will instead have an electric UFH mat thingy with a layer of levelling goo, then the posh lino bits.   The UFH mat will not extend under the shower tray, I had assumed it would just sit with the lino butting up against it, but there’s no reason I can’t screw down a layer of 6mm ply if it’s a good idea.  I assume the ply still needs priming.

 

Phew, far too much technical jargon there. I'm struggling to keep up! 😜

[Nickfromwales]

12 minutes ago, -rick- said:

 

Phew, far too much technical jargon there. I'm struggling to keep up! 😜

He's a man of many words, mostly curious ones...............perhaps he should lay off the Stella's a bit  

[Nickfromwales]

20 minutes ago, G and J said:

Thank you Nick.

 

Upstairs is Kronospan Fast Clean chipboard.  The majority of upstairs will have 6mm ply with posh lino bits glued on.  In the main bathroom we will instead have an electric UFH mat thingy with a layer of levelling goo, then the posh lino bits.   The UFH mat will not extend under the shower tray, I had assumed it would just sit with the lino butting up against it, but there’s no reason I can’t screw down a layer of 6mm ply if it’s a good idea.  I assume the ply still needs priming.

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.