base for shower tray

[dpmiller]

So I'm finally starting on the ground floor buildup. It's 50mm poured screed on 150mm insulation (100mm PIR/50mm graphite EPS). I'm unsure of how the tray works in this situation...

 

The tray is (IIRC) about 45mm thick, so I'll need to set it on ply/OSB/cementboard to get the levels right. That bit's OK. But how does said underlayer sit on the PIR, is it just bonded down or should it extend under the screed edge too, to "key" it in? It's in a corner so two walls and two floor edges.

 

ta

[PeterW]

Are you looking to get the tray dead level with the finished floor ..? What tiles / floor finish are you using and how big is the tray ..?? With stone cast trays you normally bed them on a mortar bed and this would be the same. 3:1 sand cement with SBR added I think is what Uncle @Nickfromwales recommended previously ..? That would bond rock solid to everything around it and the bottom of the tray. 

[dpmiller]

@PeterW  1400x900 trays. No I don't want flush with FFL. I'm aiming for 10mm or so above, but final finish isn't decided yet. Guessing 15mm will cover the final finish, which is likely to be tiles.

So (say) 18mm plus a thick mortar bed or 25mm and a thin bed of tile adhesive will get me to the height I want

 

I was thinking/ wondering more about how much movement there might be in the PIR rather than how the tray would be supported as such.

[Declan52]

I left a rectangular hole in my screed, used 3*2 to form the opening, to allow my finished floor to go down. Once I had my tiles picked out I could work out my final height and used a strong dry mix of sand and cement to fill the hole up to the height it needed to be. My tray was also the same size and it's heavy so it's not the sort of thing you would move when you stub your toe on it. The weight of the surrounding slab keeps the insulation from moving plus with the gap round the outside of the tray filled in once you where happy with how it set it can't move so was solid.

[Temp]

+1

How did you do the waste? On the few I've done its easier if the waste can move around a bit so it can be pulled to the underside of the tray when you screw the top part into it. So I left a channel for the pipe and trap to move around in rather than encasing it in the sand and cement. I just put a small block of wood under the trap so it wouldn't drop down so far the threaded top part couldn't reach.

[Declan52]

There was a 100 waste pipe already set in the sub floor so I used the correct cap and bend to get it roughly where it needed to be. I had a channel cut out of the floor insulation which allowed me some wiggle room for moving the pipe and waste trap. Dry fitted the tray to make sure the trap was where it needed to be and then covered the waste pipe in sand then the dry sand cement mix. 

[Nickfromwales]

The most recent one I did was the following;

Cut out DPM, cut out insulation, foam insulation to block and beam, weigh down until cured.

Then apply foam to top of upper insulation and spread DPM back on top until all in contact and keep doing so whilst foam cures so the DPM is bonded to the insulation. You could make a plywood baffle and weigh down if easier. 
 

( Note, obvious waste connections done in parallel to these processes ). 

Then reinstate DPM and tape it up to death and back. 
 

Tray then simply laid onto plywood pattresses which were foam bonded to the DPM and then flexible tile adhesive onto those pattresses and tray onto that ( cleaning and preparation of the underside of the tray carried out as required ). 
 

Tray set into place and tile adhesive left for an hour or two to cure. 
 

Cardboard funnel then made and self levelling compound flooded into the remaining void under the tray ( nearly 2 bags in this instance ) to a) fully fill the void and leave the tray ‘locked in’ at all 4 corners and all 4 sides, and b) to mechanically support the trap ( which is best practice imho ). 
 

[Nickfromwales]

That’s going NOWHERE, EVER   

[Nickfromwales]

Other option could be to use Wedi insulated panels, which you can build up in layers of differing thicknesses, to achieve the same result. DPM will remain intact as the Wedi system is watertight. Just foam around edges then, instead of pouring SLC as the SLC would bridge damp. 

Edited October 27, 2020 by Nickfromwales

[dpmiller]

Thanks all. Damp isn't ever going to be a problem anyway as the whole subfloor is poured on a Radon barrier and they're internal walls.

[andy]

On 27/10/2020 at 14:06, Nickfromwales said:

Other option could be to use Wedi insulated panels, which you can build up in layers of differing thicknesses, to achieve the same result. DPM will remain intact as the Wedi system is watertight. Just foam around edges then, instead of pouring SLC as the SLC would bridge damp. 

Right, it's about time I did some shower trays @Nickfromwales!  I'm fed up of just having a bath...

 

Thinking of Wedi Fundo Plano to keep depth as low as possible.  I will need to put some sort of mix underneath the trays to get the correct height, is this normally done using a 3:1 dry mix?  That would seem to be the easiest to tweak to get the levels bang on but has anyone else got experience of these Wedi trays?

[Nickfromwales]

On 16/05/2021 at 11:24, andy said:

Right, it's about time I did some shower trays @Nickfromwales!  I'm fed up of just having a bath...

 

Thinking of Wedi Fundo Plano to keep depth as low as possible.  I will need to put some sort of mix underneath the trays to get the correct height, is this normally done using a 3:1 dry mix?  That would seem to be the easiest to tweak to get the levels bang on but has anyone else got experience of these Wedi trays?

Wedi is a little difficult in execution, so I'd recommend a GRP former if you're planning on tiling the 'tray'? Diamond or Impey dependant of drain finish / type, and size of area. Also with Wedi, you cannot go for a mosaic less than 50mmx50mm as the tray material / construction suffers from point compression failures. Eg stiletto on a 25mmx25mm piece of mosaic = down she goes. 

[Temp]

+1

 

Wedi is ok for some things though. I used it for a tiiled wash stand. Very good for that as easy to cut. 

[andy]

1 hour ago, Nickfromwales said:

Wedi is a little difficult in execution, so I'd recommend a GRP former if you're planning on tiling the 'tray'? Diamond or Impey dependant of drain finish / type, and size of area. Also with Wedi, you cannot go for a mosaic less than 50mmx50mm as the tray material / construction suffers from point compression failures. Eg stiletto on a 25mmx25mm piece of mosaic = down she goes. 

Will look at Impey then but clearance to soil pipe is a bit tight for drain so could be slightly tricky to sort that bit.

[Nickfromwales]

15 hours ago, andy said:

Will look at Impey then but clearance to soil pipe is a bit tight for drain so could be slightly tricky to sort that bit.

Rotate the tray 180 degrees?

[andy]

57 minutes ago, Nickfromwales said:

Rotate the tray 180 degrees?

It's the vertical clearance between former and soil pipe combined with soil pipe being a wee bit close to the wall too.  I hindsight I'd have pulled the drains out into the room by a foot but hell that's for the next house now

 

From the floor level to the top of the DC2 is about 80mm I think and I don't think either will let me drop straight down into soil pipe, so need a solvent weld elbow, alas.

[Nickfromwales]

Any pics? Can't you just fit a strap on boss onto the soil stack?

[andy]

On 18/05/2021 at 17:47, Nickfromwales said:

Any pics? Can't you just fit a strap on boss onto the soil stack?

 

OK, so not the speediest reply @Nickfromwales but you know how it is, building a house and all that

 

So for good or bad I went down the Wedi route and the next challenge is to join a 40mm ABS (or 45mm depending upon if I trim the pipe back or not) to a 40mm solvent weld.  I have got a McAlpine T28M which would work fine but the knuckle would nessecitate cutting into the bottom of the Wedi base... I think if I cut it back to the thicker section then it's about the same fit as solvent weld but what can I weld them with?  The whole assemly will be filled with a 5:1 dry mix so it has to be 100% before the tray goes down.  See the pic of the trap.

[Nickfromwales]

You cannot solvent weld onto that fitting. It would either be a push fit manufacturer supplied connector or a compression fitting as you have mentioned. IIRC the Wedi formers have a metal ring on the underside, and there is supposed to be a chunky compression rubber seal ( usually supplied with the waste ) that separates the top of the part above from the underside of the tray a little. Do you have one?