Low rise shower

[MortarThePoint]

I need to fit a shower tray with its underside about 50mm above the screed for most of its area. There is a hold back in the screed in the area of the waste so deeper in that area, but I can happily mortar in bits of paving slab onto the hollowcore concrete floor there. Most legs have a minimum height greater than this and require a sheet of plywood too. What would you recommend? Options that I am considering already:

1. Mortar down 35mm thick paving slabs. With a 7.5mm bed of mortar below the slab and 7.5mm bed of mortar between the slab and the tray I'll hit the 50mm required. Will have to cut some curved slabs which could be tricky.
2. Make a timber frame out our 50mmx25mm battens and put 18mm plywood over the top of that. Then a 7mm bed of mortar will hit the 50mm required. Not too keen on adding a load of wood underneath in an otherwise all concrete setup
3. Find a 1100mm x 800mm left offset quadrant shower tray that has space underneath and can have a hole cut in its skirt. Not sure such a thing exists

 

Any suggestions for what I should dress the raised edge with? i.e. between the tray and the floor tiles

[MortarThePoint]

@Nickfromwales I'm gearing up to do this now. What approach would you take?

[Alan Ambrose]

Concrete into a former to get the shape you might have had if you had started at the beginning?

 

Or a stack of marine ply, ditto?

 

>>> Any suggestions for what I should dress the raised edge with?

 

Matching cut floor tiles? Stainless strip? It's an aestethic decision, so personal choice. Post up a photo maybe?

[Temp]

I've done two or three shower trays on beam and block floors with insulation, UFH and screed.

 

I like the waste pipe to enter the area under the shower as far as possible from the trap so the trap can move a bit in all directions. Not essential but it makes alignment a tad less critical.

 

Then I build a timber frame as per option 2. Normally treated 2*4 cut down if necessary. At least 18mm WPB on top. 

 

I cut a clearance hole in the WPB so the bottom part of the top access trap can be moved about a bit in all directions including vertically so it can be pulled up against the underside of the tray by the top part. This is why I like some unsupported length of waste pipe.

 

I do a dry run then mortar the tray down. I Used flexible tile adhesive last time as I had some already for tiling. Used a notched trowel. I screw in the top part of the trap while still soft. Later removed and refitted with sealer.

 

Two of the trays are virtually at FFL but I allow a bit of clearance so the bottom door seal doesn't rub on the tiles when you open the door.

 

 

 

[Conor]

I built a timber box topped with 18mm ply. It says on insulation and fixed to the adjacent block walls. Cut out hole and notch for waste. Best way. I fitted mine pretty much flush with the finished floor. Why are you raising yours?

[MortarThePoint]

4 minutes ago, Conor said:

I built a timber box topped with 18mm ply. It says on insulation and fixed to the adjacent block walls. Cut out hole and notch for waste. Best way. I fitted mine pretty much flush with the finished floor. Why are you raising yours?

I have to raise it to get the required waste fall unfortunately

[Temp]

Some top access traps have a higher waste than others. 

[Alan Ambrose]

I like the idea of ply over, say PIR, insulation.

[Temp]

Could easily fill wood frame with offcuts of insulation. I didn't bother as all showers on first floor.

[MortarThePoint]

52 minutes ago, Temp said:

Some top access traps have a higher waste than others. 

 

The McAlpine ST90CP10-NRV is just (53mm + seal) deep from the underside of the tray to the trap's bottom (image below). There wouldn't be enough space between the pipe and tray to fit 18mm ply though, so I would have to cut a channel in the ply all the way to the edge of the tray which could weaken it. Conversely, the trap that came with the tray (Crosswater STHFW6190, second image below) has about 33mm between underside of tray and top of pipe and is overall about 73mm deep.

 

The screed is 65mm deep over HCF and the waste pipe is already raised up 40mm above HCF by other factors. That connection point is 1.5m from the shower waste position, so these two options work out as a rise above unfinished floor of:

    McAlpine ST90CP10-NRV : 40mm + (18mm/m * 1.5m) + 73mm - 65mm = 75mm,  so about 60mm above top of tile (i.e. FFL)

    Crosswater STHFW6190 : 40mm + (18mm/m * 1.5m) + 53mm - 65mm = 55mm,  so about 40mm above top of tile (i.e. FFL)

Another thing to like about the NRV valved one is that it can act like an air admittance valve (AAV) so I wouldn't have to worry about the shower trap drying out. It's in the kids' bathroom, so they may not be showering for a few years as they are young enough to prefer a bath.

 

 

 

[Nickfromwales]

On 15/10/2024 at 11:29, MortarThePoint said:

@Nickfromwales I'm gearing up to do this now. What approach would you take?

Defo lose timber any time you can.

 

Build up with tile adhesive and cement board vs batten and plywood is my recommendation, and live a long happy (leak free) life. 👍

[MortarThePoint]

4 hours ago, Nickfromwales said:

Defo lose timber any time you can.

 

Build up with tile adhesive and cement board vs batten and plywood is my recommendation, and live a long happy (leak free) life. 👍

 

So you'd go cement board, but of the options given it would be Option (2) Mortar down 35mm thick paving slabs.

 

Cement board would be better as it allows a hole to be cut for the waste pass through rather and then still providing support to the corner of the tray past the waste. I'm guessing in reality there isn't any load applied to a tray in that location anyway. I'm a wuss about Cement Board so I think I'll go with the concrete slabs & mortar and for the corner I will screw some timber to the wall and have mortar between that and the tray.

 

I've had a wasted day trying to source plywood, but that's a whole other story.

[Nickfromwales]

Ok, but don’t use mortar, it’s crap, use flexible tile adhesive instead.

Cement is way to friable, and will just disintegrate over time removing any support you assumed it would provide long term.

 

If you can fit / cut a paving slab then cement board should be a doddle?! 
Again, use tile adhesive regardless not mortar for bedding those too. 

[MortarThePoint]

19 minutes ago, Nickfromwales said:

Cement is way to friable, and will just disintegrate over time removing any support you assumed it would provide long term.

 

Interesting as I gravitate towards mortar because it's a material I'm much more familiar with. Would adding SBR give you more confidence, or you'd still air towards the flexible tile adhesive.

 

I know some tray manufacturer's suggest a very weak sand:cement mix at perhaps 8:1 which I can appreciate would be pretty weak. I'd be more inclined towards 6:1.

[Nickfromwales]

5 minutes ago, MortarThePoint said:

 

Interesting as I gravitate towards mortar because it's a material I'm much more familiar with. Would adding SBR give you more confidence, or you'd still air towards the flexible tile adhesive.

 

I know some tray manufacturer's suggest a very weak sand:cement mix at perhaps 8:1 which I can appreciate would be pretty weak. I'd be more inclined towards 6:1.

I’ve been doing this for 30+ years chief, do as the wise Welshman says lol. 😜 

[Nick Laslett]

What about a 50mm thick piece of marmox board? Cut hole for waste, tile adhesive to stick down. Tile adhesive to fix tray to board. They actually do 60mm boards, or 100mm XPS plinth too.