Longer thread shower waste

[mitchino]

I ordered a McAlpine 90mm x 50mm shower trap for my walk-in shower. The base will be 18mm ply with the shower tray bedded in mortar on top. I don't think the threads of the top half of the trap are going to reach the threads of the bottom half when I assemble everything. I really need more threads on the top part of the trap. Do McAlpine make such a thing? The other alternative is to widen the hole in the plywood so the whole trap presses up against the bottom of the tray, but the tray is quite thin around the plughole and I wanted to support it with the ply. What is the solution?

 

[ShaunCorbs]

You don’t tighten the tray into the ply aswell

 

[mitchino]

ah ok - always tighten waste straight onto the tray?

 

[ShaunCorbs]

Yes

 

[mitchino]

That seems like a fairly large area of thin shower tray around the waste that will have no support from the ply base? I found this long waste, can I not use that to solve the problem? Is the ply likely to get wet if the trap secures to it?

McAlpine Long Waste for 90mm Shower Traps ST90W/BODY-L

Free First Class Delivery, Same Day Dispatch, Brand New, VAT Invoice upon request.

www.theonestopbathroomshop.co.uk

 

[ShaunCorbs]

It’s designed for this there stronger than you think

 

[mitchino]

Can you explain why I can't bridge across the ply and tray with the waste? Is the ply likely to get wet? Sorry to go on and on!

 

[Duncan Stirling]

Can you explain why I can't bridge across the ply and tray with the waste? Is the ply likely to get wet? Sorry to go on and on!

Yes, the ply will get wet. As mentioned, affix trap to tray and cut out plywood around trap.

 

[AdrianP]

You will likely end up with a very sorry situation if you try that! Think of the routes available to the water and where the seals are, and what keeps them tight in the long term:

• Firstly there's the gap between underside of trap top and topside of tray. You'd probably be ok there (initially) if you sealed it well , but any water that did get through would no longer be protected by the main seal which is normally provided on the underside of the tray, it'd be straight into your ply. The ply would start to rot pretty swiftly, after which there's nothing to hold the top seal tight. That top seal is going to be dependent (for it's tightness) upon there being zero give through the ply and mortar including when weighted by occupants. Are you sure that ply won't compress just a little over time?
• Secondly, once in the trap the water will migrate back up the trap thread where it will soak into the ply. I suppose you could smear a load of silicone on the thread, but that isn't normal practice, and I wouldn't recommend it.

If you want to keep the hole in the ply as small as possible (and you have enough space beneath the tray) I sometimes use a standard bath trap (type without overflow connection) or p-trap connected to a top access waste (eg: BES 10374/10376/10377)?

 

[mitchino]

Thanks for that