Fitting a stone resin shower tray on plywood

[George 3G]

Hi all,

 

I'm in the middle of a bathroom renovation and I'm crossing off the last few jobs before the tiler comes. The biggest job left to do is to fit the 1700mm x 760mm Merlyn stone resin shower tray. I've removed the old chipboard floor, added extra noggins to the floor joists for additional strength and laid a new 18mm plywood floor. The bathroom is only 1700mm x 2000mm and there is a steel under the doorway so the floor is pretty rigid but there is a 10mm or so drop across the bathroom floor (over the length of the shower tray). I wanted to make sure my plan for fitting the tray is correct, I've done some searches on here and found some very helpful advice, especially from @Nickfromwales but I just wanted to make sure I hadn't missed any steps in the process. I'm a complete novice and haven't done anything like this before!

 

So as it stands, my plan is:

 

1. Clean back of shower tray to remove any trace of mould release agent
2. Prime underside of tray with Ultra Tile Fix Primer
3. Prime Plywood with Ultra Tile Fix Primer
4. Lay either Jackoboard or Hardie Backer Board with tile adhesive and screws to tray area of floor in a step form to "bulk out" thick areas of tile adhesive to avoid any adhesive sinkage.
5. Back butter shower tray with 10mm trowel
6. Lay tile adhesive over Jackoboard / Hardie Backer Board with 10mm trowel
7. Fit Tray
8. Lay Hardie Backer Board to remainder of floor which will have a self leveling screed laid over it by the tiler to level.

 

I also want to add some CT1 to the three sides of the tray that contact the Wedi board wall, what is the easiest method of doing this on a tray that is in contact with the wall on three sides?

 

Lastly I plan to use either of these adhesives for fixing of the tray and the Jackoboard / Hardie Backer Board to the plywood floor, is there a preference between the two or can anyone recommend a superior product? I really want to have as much time as possible to ensure the tray is level before it sets.

 

Ultra Tile Fix ProFlex SPES Standard Set Flexible S1 Adhesive White 20kg

BAL Flex One Tile Adhesive White 20kg

 

Have I missed anything or are there any tips to help make the process easier for a novice?

 

Any advice will be greatly appreciated, thanks!

[nod]

I would just bed the tray directly on to the ply with a flexible tile adhesive 

[Nickfromwales]

Avoid step 2, just damp it with a few tubs of a wet sponge before laying onto wet adhesive.

2 minutes ago, nod said:

I would just bed the tray directly on to the ply with a flexible tile adhesive 

+1

There isn’t a need for the backer board, and I’m not a big fan of it tbh. Flexible TA is fine for a 10mm runoff, and I’ve always used Ultra unless the client has had BAL included with their bathroom / tile order.

To get the CT1 done, just seal up after the tray is laid, if you don’t have any ‘wiggle room’ to “goop up” first. 
 

[Nickfromwales]

 

[George 3G]

4 hours ago, Nickfromwales said:

Avoid step 2, just damp it with a few tubs of a wet sponge before laying onto wet adhesive.

+1

There isn’t a need for the backer board, and I’m not a big fan of it tbh. Flexible TA is fine for a 10mm runoff, and I’ve always used Ultra unless the client has had BAL included with their bathroom / tile order.

To get the CT1 done, just seal up after the tray is laid, if you don’t have any ‘wiggle room’ to “goop up” first. 
 

 

Okay great, that's made my life easier and saved me money, thanks! The Ultra TA states it can make up to a 20mm bed too so that will be plenty, I only suggested BAL as I had read good things about them! Should I still back butter or notch the back of the tray?

 

There isn't any wiggle room between the tray and Wedi board on the walls, will this not cause me an issue trying to force CT1 down the gap? Is it not worth at least applying some to the three sides prior to laying the tray, or will this just end up spread down the three Wedi boarded walls?

 

I do also plan to use this sealing kit between the tray and the Wedi board once the tray is in and set:

https://www.rubberduckbathrooms.co.uk/abacus-no-more-leaks-4m-shower-and-bath-sealing-kit

 

Thanks again!

[Nickfromwales]

Following my advice / techniques in the thread I linked by creating a bond / up-stand in one would be ample. No need for that product afaic, but if you’re happier ( feel more confident ) to apply that then there’s no reason not to use it.

You can ‘paste’ the 3 sides round of the Wedi with clear CT1 immediately prior to dropping the tray in, and then mask up and top coat with more so as to have a wet-on-wet bead of CT1 all the way around. 
Don’t worry about getting it a bit mucky, as cheap baby wipes will clean it all off perfectly well. Use loads of them, one or two wipes with each before discarding into a carrier bag as you go. 
Masking the tray before you start the installation would help. I use 2” PVC electrical tape. Stick the tape just shy of where the tiles will stand out from the walls. Peel off the masking the second you finish applying the top seal of CT1 and have done the clean up with wipes. 

[George 3G]

Hi Nick, thanks for the concise instructions, I'll do just that!

 

Can you clarify this first paragraph for me please? Are you referring to the CT1 or my suggestion of back buttering / troweling adhesive onto the back of the shower tray?

 

9 hours ago, Nickfromwales said:

Following my advice / techniques in the thread I linked by creating a bond / up-stand in one would be ample. No need for that product afaic, but if you’re happier ( feel more confident ) to apply that then there’s no reason not to use it.

 

 

 

Also from the thread you linked above, when you say "tool displaced sealant" are you advising that when you drop the tray in, any sealant that is squeezed out from between the tray and the wall you spread up the wall with a filler knife or similar?

  

On 20/08/2017 at 23:47, Nickfromwales said:

@MAB

Sorry, I missed this somehow. 

If using tile adhesive, you need to be very sure there are no contaminants from manufacture on the underside. I've had a few which have some slimy stuff ( a mould release agent of sorts I suspect ) and nothing will stick to that.

I'd use Sikaflex between the tray and the backerboard, applied whilst bedding the tray into the tile adhesive. Use that to create the fundamental seal between the tray and wall, and then tool the displaced sealant onto the BB to create an upstand seal ( have you read my comments in the tanking / wetroom thread )?

 

Thanks again @Nickfromwales, I owe you a beer, or three!

[Nickfromwales]

The product I refer to there is that "no more leaks shower seal" item.

9 minutes ago, George 3G said:

when you say "tool displaced sealant" are you advising that when you drop the tray in, any sealant that is squeezed out from between the tray and the wall you spread up the wall with a filler knife or similar?

Yup. So all of that gets done as one wet application. You'd butter the Wedi with CT1 immediately before dropping the tray in, then apply an excessive amount around the 3 sides, and then you'd tool that into place as per that thread to create the up-stand.

12 minutes ago, George 3G said:

Thanks again @Nickfromwales, I owe you a beer, or three!

My second favourite currency lol.

[George 3G]

Thanks @Nickfromwales!

 

So my to do list is as follows:

 

1. Clean back of shower tray to remove any trace of mould release agent
2. Prime Plywood with Ultra Tile Fix Primer
3. Back butter or trowel underside of shower tray
4. Butter Wedi board with CT1
5. Butter three sides of Wedi board with CT1
6. Fit Tray into final position
7. Spread displaced CT1 up Wedi board and remove excess on tray with wet wipes
8. Lay Hardie Backer Board to remainder of floor which will have a self leveling screed laid over it by the tiler to level.

Have I missed anything please? I also read one of your suggestions in another thread regarding test fitting the waste prior to fitting the tray to count how many turns are required. When I removed the tray off the old sand and cement base the plumber who had attempted to fit it had not only used silicone when Merlyn advise not to but the waste was out of place by about 10mm to the tray, straining the components. I need to check that the waste has not been damaged from this!

[George 3G]

Another question, what type of plywood should I be using for the bathroom floor? 

 

Thanks!

[Temp]

Some form of WBP plywood. A good timber merchants may stock several grades. To be honest it ranges a lot in quality and price. I got some from a chain beginning with W that was junk. Some places call their best "Marine Grade" but I'm not sure thats an official term.

[Nickfromwales]

On 11/04/2022 at 17:47, George 3G said:

Have I missed anything please?

Nope, all good.

6 hours ago, George 3G said:

Another question, what type of plywood should I be using for the bathroom floor? 

 

Thanks!

For under the tray or for the remainder of the bathroom flooring? If the latter, green P5, for the former as per @Temp’s reply.

[George 3G]

Brilliant, thanks both @Tempand @Nickfromwales !

 

So I think I have one more question before I'm ready to lay the tray. The plumber who carried out the prep work and who has since left the job left this piece of studding at floor level (see photo below), he then boarded the wall with the Wedi board flush to it and then used some Wedi self adhesive joint tape over to cover the joint. Something I wasn't happy about at the time, especially as the shower tray sits against this wall.

 

I have removed the tape this morning as if I am going to leave it like this prior to tiling, I think the fixing screws/washers that the tape sticks over should at least be sealed with Wedi 610 first. You could see the tape lifting off these where it hadn't stuck properly. My question is, is it okay to repeat what he had done? Or is there a better way of preparing it. I really don't want to be altering that piece of studding if possible.

 

Thanks again all!

 

 

[George 3G]

Or what if I was to just cover the whole area in Wedi 610 sealant? It says its suitable for using on wood!

[Temp]

Weds 610 is probably as good as anything because it will be designed not to dissolve the foam.  You could embed some mesh tape in the 610.

 

 

 

 

[Nickfromwales]

4 hours ago, Temp said:

Weds 610 is probably as good as anything because it will be designed not to dissolve the foam.  You could embed some mesh tape in the 610.

 

 

 

 

Yup. I’d go with that. 
The guy is a cock for not having the Wedi drop to the floor. Terrible detail there. 
610 is good stuff too. 

[George 3G]

Thanks both! The plumber indead was a cock, and it's thanks to his mistakes I've had to inherit the job to finish it ready to be tiled!

 

It's good to hear I was right to suggest covering that exposed studding with Wedi 610 and I've done just that, this morning, so thanks both!

 

Would it be a good idea to use Wedi 610 down the three sides of the tray that contact the wall? Or should I stick to using CT1? I have both at home so it doesn't make a difference as far as that goes.

 

Thanks!

[Nickfromwales]

Is there any timber behind the bottom of the Wedi panel eg directly above that timber? Push against it and see if it moves inwards.

[George 3G]

Now I've lifted that part of the floor I can actually get my hand up behind one end of the exposed studding and I can feel a second timber above it.

[George 3G]

Actually, it may be plasterboard!

[Nickfromwales]

Just now, George 3G said:

Actually, it may be plasterboard!

Push the Wedi. If it moves you’ve still got work to do  

[George 3G]

The three washers shown are into studding but I'm not sure if there is a second horizontal piece of studding sat above the exposed piece shown in the photo.

 

I've given that whole area of Wedi a push and it moves but only absolutely minutely, no more than it does between the fixings further up the wall.

[George 3G]

I just searched through my phone and found this photo from when the tray was test fitted, you can see the second stud sat on the lower stud with red paint on that is now exposed! Panic over!

 

He obviously just sat the Wedi on top of that lower stud instead of cutting that step away and fitting the Wedi board all the way to the floor.

 

Out of interest @Nickfromwales, what would I have had to do if that second stud wasn't there? Your posts above sounded ominous! 

[Nickfromwales]

Drill a series of holes and pump full of gap-filling expanding foam is my normal solution there.

[George 3G]

Well everyone, it's in, it's level and it's solid as a rock! Thanks to @Nickfromwales and @Temp for their advice, I couldn't be more grateful!