Shower Tray Waste Routing

[SproutsDad]

In a new downstairs utility/shower room I have a shower tray waste to route below plywood floor into solvent weld 32mm new pipe. Acess is limited beneath by solid underfloor with 100mm joist floor and 22mm plywood floor.

I have bought the MacAlpine ST90CP10-70 shower trap, see photos, because it is rated as a good one. I didn't want to use the free one supplied with the tray which looked flimsy and already had the thread crossed.

>> Note - I intentionally want to keep the tray close to the floor because it is for easy near-level access showering. I want to avoid building up a structure beneath the tray.

>Pipework routing - I have a number of options to route this but have to consider dropping the tray in and probably doing all the sealing and tightening up from above, which I have seen done in a couple of videos.

I have shown three suggestions A, B & C in the photos and, although A is the shortest and probably least likely to present leak problems in the future (?), it is also rigid and if dropping the tray on from above, it offers little/no room for adjustment.

Suggestions please and your view on which, if any of these I should go for.

> Sealing - Should I use a sealant/silicone around the rubber seals when fitting?
I understand that it would need to be a neutral cure to not affect the rubber seals.

> Mortar bed under tray? - this tray is very thick GRP and robust, plus it is extremely close to the floor - 15mm bottom of tray to underfloor.
Do I need to bed it in on mortar? It is not a resin & sand type already filled.
Maybe sounds crazy but could expanding foam be used to fill the void - taking care not to gunge up the waste trap?

All suggestions gratefully received.

 

[muggles]

When you say 32mm pipe, do you mean 40mm? 32mm is for basins and is too small for showers. It should also only be used for a max of 1.7m, 40mm can run up to 3m, if you're going further than that 50mm should be used.

I'd only consider A as an option if I was doing it - flexible pipes like that are natural hair and soap traps, and can sag over time as well, leading to blockages

I use Sticks Like Sh*t to seal up the waste - neutral cure and really strong

The mortar bed is to provide support and prevent flexing - foam won't do that. Any movement in the tray after installation will eventually cause a leak, and GRP trays have considerably more flex than stone resin ones

 

[Hugh Jaleak]

I'd go personally for the shortest route, plastic pipe will allow a slight flex, if the tray is installed correctly, there shouldn't be an issue. The rubber washer provided should be ample to make a seal, you don't need anything on the internal side of the tray, as they are not designed to hold water, like a bath or basin.

What are the manufacturers instructions for installing the tray? Follow these to the letter or any warranty claims will be void. I certainly wouldn't use expanding foam, as you've no idea what its going to do as it cures, and again, will likely invalidate any warranty on the tray.

Waste, needs to be minimum 40mm from a shower. If the existing waste is only 32mm, it needs upsizing from where the tray connects to the drain or stack.

 

[Hot&Cold]

Never liked them shower trays where the waste outlet is in the tray entrance area,have to remember its a weak spot and it will be walked on a lot, there is no support under the trap. Waste connection in the opposite corner yes.

Also consider the raised domed mushroom cover could not be designed for standing on and feel uncomfortable under foot. I prefer these mcalpine outlet/traps.

The 40mm existing drain pipe can be teed into but it needs a defined drop, bends kept to a bare minimum and of the shortest run possible.

Option A is sending the shower drain water in the most direct route and is not slowed by the bend and/or flexi pipe.

How many other basins,sinks,bath use the existing 40mm drain pipe ?

The tray is usually bonded to the plywood with building adhesive CT1 is good but consult the tray installation instructions.

expanding foam is not needed.

Happy plumbing

 

[SproutsDad]

Yes it is 40mm, 32mm on an adjoining basin. The whole new 32/40/50 into 100mm waste network has been done new by a plumber for a washing machine, shower, kitchen sink, wash basin. He is too busy now to continue so I am picking it up. I'm happy with solvent weld Hep2o etc but need and appreciate some help on this shower.

Thanks everyone for the replies - well I did ask!

Glad that you feel Option A is the best.

So maybe I should have asked before buying the shower tray, but I have it now and won't be binning it. But I can look at :-
> Waste trap - Swapping the waste trap for the one that Old&Bold suggests.
I can't see it on the McAlpine site if it is their's? Can you please give a model number etc, who sells it?

The one I have came from Screwfix, it can go back. I had been to plumbing merchants first, but they were more expensive even with trade discount, replying "Suppose I can order one mate, but it'll take a week" ???

> Support for the shower tray - it is of a thick and robust section and with no apparent flexing. But if you feel it won't be robust enough, can I .......
a - bed it in mortar all over or in key load areas?
or
b - bed some battens into the underside level with the floor. << Preferred?

Thanks again.

 

[Hugh Jaleak]

This is available from Screwfix, https://www.screwfix.com/p/floplast-shower-trap-chrome-40mm/16391 should be ok to swap with what you have. If you prefer the McAlpine, try an independent Plumbers Merchants, the chains tend to be expensive for the DIY'er.

I would still be referring to the manufacturers instructions for installing the tray, failing to comply with these, and the tray fail during the guarantee period, I highly suspect they'll refuse any claim under the guarantee if the tray hasn't been installed as per their instructions. It may be designed to allow some slight movement, preventing that movement by adding support when not required could do more harm than good.

As an aside, how many other appliances are connected to that waste pipe? Showers ideally need a dedicated waste, right through to the stack or gulley.

 

[Hot&Cold]

http://mcalpineplumbing.com/traps/shower-traps-accessories/st90cp10-70c-90mm-shallow-shower-trap (target price £28)

That shower tray needs to be bonded to the ply floor,unless the supplied instructions say different.

Is the base of the tray fitting flush on the ply if so run a few circles of CT1 and place it down and level (walk in the tray) to ensure its bonded down.

 

[SproutsDad]

Thanks, that is the same trap that I already have but the top cover is flat and chromed brass instead of the domed one I have. I will try a merchant for it, Screwfix don't have that exact one.

The shower tray will be directly on the ply at the vertical flange/edges which are about 35mm high. The perimeter is the only bit which touches the ply floor. The underside of the tray area is suspended about 20mm off the ply underneath. It was for that reason I had thought to put battens bonded into the underside of the tray resin/GRP and levelled off to span the void between the tray underside and the ply floor.

The 40mm waste run goes into a 50mm for 500mm length then runs into the 100mm running out of the house, no vertical stack because this is ground floor.
The only other thing on this 40mm dia run is a washing machine, in the same room and highly unlikely that a wash load and the shower would run at once.

Thanks again.

 

[SproutsDad]

Not so keen on the Floplast, a few low star reviews on it, but thanks. I will try to track down the McAlpine suggested by Old&Bold.

Sealing to tray - What about the neutral core silicone, is it any good on rubber ring seals?

 

[Hugh Jaleak]

Would recommend you keep the washing machine and shower on separate wastes. Over time, the waste is likely to gunge up, should the washing machine empty, (and they pump out at a fair rate), and the waste not be able to handle the flow, you'll have it all reappear in the shower tray, if it overtops the tray, you'll have a mess....

You do not need any kind of sealant on the waste, the rubber seal supplied should suffice. Sealants can affect the plastic, damaging the tray.

 

[SproutsDad]

Thanks for the advice on the shared waste. I will separate them but can they later meet up in a 50mm or do they need to go separately all the way to the 100mm stack?
Currently the new network done by the plumber has 32mm's going into 40's or 50mm's, a couple of which join into the 100mm separately then out to the street.
A new/separate washing m/c waste directly to the 100mm stack, that one may not be so easy - not sure if I can get access to the 100mm under floor to join into it. Will check.

Thanks

 

[Hugh Jaleak]

I would personally, keep them separate if you can, although joining them both into the 50mm pipe is vastly better than both on a 40mm. You'll notice eventually if the shower is slow to drain, washing machine will have a higher flow rate so will probably take a lot longer to gunge the pipe up.

 

[SproutsDad]

Thanks Hugh. It would be major surgery to lift the glued down ply floor to get a dedicated 40mm from the washing m/c to the main 100mm outlet.

However, I have access to the 50mm and the two 40mm's currently meet at a branch in the existing 40mm run, which then later goes into the 50mm and from there out to the 100mm underfloor stack.

>> Proposal - see sketch, I could replace that 40mm part so the washing m/c and shower each join into a shared 50mm close to each of them.

In fact the washing m/c could run almost entirely in 50mm as the main 'artery'. The 40mm shower feed would meet the 50mm much further down the run, much closer to the 100mm final outlet.
See photo of sketch if it helps .

Thanks

 

[Hugh Jaleak]

40mm run from washing machine should be ok on the initial run, upsize to 50mm at the tee where the shower couples in, although you may have to look at measures to prevent the washing machine siphoning the shower trap! What length is this run too? Should really ensure compliance with regs.

 

[SproutsDad]

Thanks for the reply, this seems to be growing, but best sorted now rather than a mess if the washing m/c waste overflows or backs up!

But thanks for the alert. I have paid a plumber to take it this far, so I don't know what his thinking was regarding anit-syphon?
I have an open floor and a building control guy who will need to sign this all off. So it's got to be right before closing the floor up with T&G 22mm ply.
Thanks for the alert especially if this might not be compliant / to regs.

There has been no mention to date of anti-syphon apart from on the sinks and basin, but I think those have anti-syphon bottle traps.

Washing machine waste - The plumber has left what looks like a standard WM3 McAlpine, separate trap with standpipe, an open top trap kit.
But reading the accompanying installation instructions, it looks like the McAlpine WM4 +TV1 TeeVent system would be better because it incorporates a non-return valve. Quoting from their instructions they say........

"The TeeVent system, which incorporates a non-return valve, provides an air break and enables the waste system to be sealed. This syestem has the advantage over a standpipe becaues if a blockage should occur, the non-return valve prevents flooding". (McAlpine)​

Q? >> Based on the above, should I continue with the WM3 standpipe or swap for a different arrangement with non-return valve?

Waste system design - see updated sketch with dimensions. What do you suggest I do? From the run lengths seen in the sketch should I continue with it as drawn, i.e. extend the 50mm to just beyond the shower and then continue to the washing m/c in 40mm, with / anti-syphon / non-return valve?

Thanks again for the advice, much appreciated.