Shower tray into a screed floor

[bandejapaisa]

I've got the DPM + insulation down on a block and beam floor. It's 150mm PIR. Screed will be 55mm + 20mm floor covering in the bedroom.

I have an adjacent new bathroom which I wanted to be a tiled wet room, and want this level with the bedroom floor at the door threshold, or very close.

I also want the shower tray flush with the rest of the bathroom floor, which means figuring it out now, before I lay the screed.

I'm looking for any tips on embedding the shower tray/forma in the screed. I'm thinking I need to have some plywood underneath the tray first, at least to make up the height, but is this enough support if I lay this on the PIR and then the shower tray on top of that? I'm assuming once the screed is down, the weight of this means the PIR isn't moving - just feel i need something more solid underneath the tray....18mm ply minimum?? Would I let the screed flow over the edges of the plywood to hold it in place... ie. by shuttering it off?

So many questions, and searching for the answers....

 

[23vc]

You can either buy a wet room shower former exactly for that purpose, or freehand the screed to a sensible fall, after fitting the gulley. I’ve done it twice, and freehanded the screed both times. Worked a treat.

Edit - just realised your probably doing a free flow liquid screed, whereas I’m talking about sand and cement. I’ve heard of people putting a block of insulation in, pouring the screed around it, then removing it and fitting the former , so that could be an option.

 

[bandejapaisa]

Thanks.

Yes. I'd be getting a liquid screeder to come in. Also yes, I read about the block of insulation being put in and screeding around it.

I'm fine with doing those things. My main concern is, can the shower former just sit on top of 150mm PIR??? My common sense is telling me no and I should put something more solid underneath it.

 

[23vc]

I think the idea is you allow the screed to flow under the former, or under the block of insulation that’s going to be dug out and replaced by the former.
So I’d be thinking something like:
- Your base PIR
- 4 half bricks or something to get the right height for the bottom of the former, and to take each corner of the shuttering insulation block
- The shuttering insulation block with some additional weight on top to stop it floating

Then Pour the screed, which would flow under the shuttering block, taking away your worry about how it’s supported. Then it gets ripped out and replaced by the former, which will be at the correct height dictated by those 4 brick/supports.

 

[robinbanks]

I’ve heard of people putting a block of insulation in

Block of insulation (i.e. a cuboid of polystyrene-esque material) like a shower tray former (i.e. a cuboid of polystyrene-esque material) you mean?

Saves taking it out that way..

which will be at the correct height dictated by those 4 brick/supports

Just so I'm clear, are you proposing to sit these bricks on top of the underscreed insulation, or do they bridge the insulation layer?

 

[23vc]

Block of insulation (i.e. a cuboid of polystyrene-esque material) like a shower tray former (i.e. a cuboid of polystyrene-esque material) you mean?

Never used a former, but used sacrificial PIR to shutter stuff like this a lot. If you can do away with the insulation and stick the former straight in, then great. But you’d have to be absolutely bang on and ensure it doesn’t move, whereas shuttering it and bedding it down after the pour, gives a bit more margin.

Just so I'm clear, are you proposing to sit these bricks on top of the underscreed insulation, or do they bridge the insulation layer?

On top. It makes the gap that screed flows into, to support the former/shuttering.

 

[robinbanks]

can the shower former just sit on top of 150mm

It's not the right height. A pre formed insulation block incorporating a fall to a welded-in drain hole is typically 20 to 35 mm high and you're pouring a 55mm screed. If you're looking to embed it so its top surface is flush with the surrounding screed I'd put some timbers across the room at the height the top of the screed will be then put the former under the timbers together with some packers that will keep the fall shape of the former if it flexes when it floats. When the screed is being poured lift the former so the screed flows under it and let it float til it's held down by the wood. Keep pouring the screed so it rises up the sides to flush. I'd pick a 20mm tray if you're installing a 55mm screws and I'd aim to have a ring of thicker screed all around the tray. Ensure any insulation under the tray is well fitted and not rocking/flexing, and also ensure that the drain/trap fitted to the former is fully serviceable from the top. The simplest solution I've found to insulation that rocks or flexes is to stand either side of the rocking fulcrum and cut the top surface of the insulation so it snaps and forms around the fulcrum

 

[Wayners]

Have you watched

 

[bandejapaisa]

Thanks all for responses. Was very useful getting various techniques. I'll crack on.

 

[robinbanks]

Have you watched

Don't think I'd be pulling my 22mm P5 eggerdeck out to replace it with 18mm ply ..

Not sure how relevant the rest of the video is for a wet room tray but I didn't watch it all