Replacement shower tray base puzzle

[Beverly27]

Following on from my previous post, we have now taken up the shower tray and removed the plaster on which the tiles were mounted. The causes of the dampness and leaks from the shower installation are becoming increasingly evident, including today's discovery, shown in the photo, of the shower tray mounted on blobs of adhesive and some rubble rather than a solid base.

It might be tricky to see from the photo, but the ply upon which the tray was mounted runs under the floor tiles (beneath my feet in the image) rather than being a separate section. Given the rest of the job, I suspect it may not be marine ply. It's a bit springy, so there are likely no noggins to support it. I suppose I need to remove it to install a marine ply platform for the shower tray that is solid. How would you suggest I do this? I have considered cutting through the ply directly adjacent to the floor tiles, with a circular saw, but I don't want to cause more problems.

 

[Madrab]

Multitool and cut straight along the ply. Looking at the colour though it may be HW/WBP.

You need to check the subfloor, if there was water ingress. That and lift the floor and check underneath and strengthen if req. That pipework could have been routed better - holes through the framing would have been my choice or kept it underfloor.

 

[Beverly27]

Multitool and cut straight along the ply. Looking at the colour though it may be HW/WBP.

You need to check the subfloor, if there was water ingress. That and lift the floor and check underneath and strengthen if req. That pipework could have been routed better - holes through the framing would have been my choice or kept it underfloor.

Thanks, Madrab, I'll do as you suggest. Agreed about the pipework. Is there any point in having it re-routed, though, now? I have no idea.

 

[Madrab]

All depends on whether it's sealed behind the wall panel or does it sit inside the shower space? If it can compromised the sealed from the shower into the wall then ideally it should be moved.

 

[Beverly27]

All depends on whether it's sealed behind the wall panel or does it sit inside the shower space? If it can compromised the sealed from the shower into the wall then ideally it should be moved.

Oh goodness. Do you know whether rerouting the pipes would be time-consuming and costly? I'm on a tight budget.

 

[Madrab]

It all depends on where the left wall (plasterboard?) is sitting and where that pipe actually ends up in relation to the tray and the wall? If the shower is flat on that board then does that pipework actually sit alongside the edge of the tray? If that's the case then that's a real area of concern when it comes to making a waterproof seal. How was the tray sealed up to the left wall if that pipework is in the way?

Or does the tray actually sit above the pipework? Having trouble seeing how that would all end up. What does that pipework supply? Given it's soldered then it would take a little work to have it moved into the wall. What's under the floor?

 

[Beverly27]

It all depends on where the left wall (plasterboard?) is sitting and where that pipe actually ends up in relation to the tray and the wall? If the shower is flat on that board then does that pipework actually sit alongside the edge of the tray? If that's the case then that's a real area of concern when it comes to making a waterproof seal. How was the tray sealed up to the left wall if that pipework is in the way?

Or does the tray actually sit above the pipework? Having trouble seeing how that would all end up. What does that pipework supply? Given it's soldered then it would take a little work to have it moved into the wall. What's under the floor?

The left wall, with the shower valve, was plasterboard mounted on OSB. It sat just above the copper pipes, which protruded a little in front of this plasterboard, and so this wall was a few mm away from the edge of the tray, but the tiles on it sat on the tray, sealed to it with silicone.

The copper pipes protrude 32mm from the stud work and were 35mm high from the surface of the 12mm base ply on which the shower tray sat. The face of this ply was 25mm beneath the level of the floor tiles, as shown in the attached drawing.

The plan (below) is to sit the new tray above the level of the pipes and to build the aqua board (Abacus Elements) wall out so that it will directly abut the tray and run down the side of it before stopping just above the pipes, so there’s no gap between the tray and aqua board. I don’t know what the pipework supplies. Under the floor was insulation. It seemed in good shape, apart from the far corner, which had black mould. We’ll replace this part of the ceiling (of the room below).

The plan, also attached, is to:

1. Build the (left) wall above the pipes out by 20mm, possibly with one sheet of 11mm and 1 sheet of 9mm OSB, unless there’s a better way to achieve this 20mm, plus the 12mm aqua board, making 32mm. This means that the aqua board will then abut the side of the shower tray.
2. Install noggins on the joists for extra support, although not sure if needed or what to use for these, to mount a 30mm marine ply foundation to sit the shower tray on. The shower tray is 40mm in height, so the aqua board wall above the copper pipes will run 23 mm down the side of the shower tray, with no gap between them.
3. Use flexible waterproof tape that will be tiled over and attached to the aqua board and tray so there is a waterproof barrier between the edge of the tray and the wall.

I’m keen not to reroute the copper pipes due to the cost, but I want to ensure we don’t have any more leaks. I’d appreciate any feedback because I don’t know if this plan is watertight (!) and if I should do anything differently.

 

[Madrab]

Ok, looks like it will be a better option than it was before, though I would always look to tank the wet space. Fit the wall boards etc, then you can use a waterproofing kit with tape to seal in all the edge/corners create a waterproof skin.

Look at the Mapei waterproofing kit or similar

It's not expensive and comes with the primer, tape and paintable membrane, it's one of the best budget kits available IMO, give it 2 or more coats up to head level.

When fitting the tray then drop the tray down onto the ply into the space then lift at one end and drop in the adhesive/fixing medium then drop back down a few mm out from the walls, be quick and fill the wall gap all the way around with a good quality silicone without any spaces, especially in the corner and then push the tray tight home to the wall. That will create the wall to shower seal all the way around, clean off the excess that's squeezed out flat to the tray top and then leave to dry for 24hrs.

When you tile back down then seal again (don't grout at the tile/tray threshold, use silicone), that way you are creating a 3 layer seal.