# How best to seal a shower trap?



## askew70 (1 Aug 2007)

Our shower trap is leaking and I am trying to repair/replace it. It all seems very straight-forward except for the question of how to seal between the threaded waste flange and the opening in the shower tray.

I bought a new trap, whose instructions say to use silicone sealant between the flange and the shower tray, but the sales guys where I bought it said that no silicone sealant is needed. I fitted it dry and it didn't leak when I poured a bucket of water into the tray but did leak the next time someone had a shower.

I am wary of using silicone sealant, as the motion of threading the flange into the trap will move the sealant and perhaps leave gaps. If it continues to leak once the sealant is dry then the only way to remove the flange to try again will be to cut it out, which won't be easy.

The original flange had just a thin washer between it and the shower tray, but I haven't been able to find a new version of this washer (it feels like a form of soft polystyrene). I'm not even sure that a washer alone is adequate - the plumber that fitted it was incompetent (e.g. he fitted the shower enclosure without mastic between the back of  frame and the tiles so it leaked the first time we used it) so I have no faith in how he chose to seal it. Also, we don't know how long it has actually been leaking (the shower is in place for a few years, but only recently did enough water build up for it to soak through the ceiling below) so it is not clear whether the washer ever provided a watertight seal.

So, is the best way to seal between flange and shower tray to use appropriate silicone sealant, or to use an appropriate washer? Thanks for any advice.


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## Leo (1 Aug 2007)

You should always use washers where provided. In an ideal world where the parts are of good quality (threads match and mating plates are smooth and flat) and you can get easy access and ensure a very tight connection, no silicon should be required.

You can also get non-setting sealants that will allow the dismantling of the connections in future. Apply a good coat to the threads, and the action of screwing the connection together should ensure a full seal.
Leo


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## askew70 (1 Aug 2007)

Thanks Leo. The new trap came with no washer (just a washer to sit between the trap and the base of the shower tray), so it certainly seems to rely upon silicone sealant alright (the instructions  mention "neutral silicone sealant - Dow Corning 794 or equivalent"). 

One problem that I face is that the hole in the shower tray is sunk lower than the surrounding surface, and it is impossible to see whether the waste flange sits snugly against the sloping edges of the hole - putting in a lot of sealant, and hoping that the excess will squeeze out, might work but it might be hit and miss. 

A "miss" would be a lot easier to deal with if using a non-setting sealant. When you mention a non-setting sealant are you referring to something like Plumber's Mait?


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## Leo (1 Aug 2007)

Plumber's Mait is more of a putty, and so you're probably less likely to get a good seal all around the threads.

If the instructions call for silicone, I'd go with it. DC 794 is a 100% silicone, unlike many of the cheaper products out there. There are other quality silicones on the market, the Sealux one is carried by a lot of the plumbing and tile outlets.
Leo


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## kittycole (1 Aug 2007)

Hi,
I would use mait. Its not the threads that are leaking, its more likely to be where the trap sits on the tray. you use mait like mala and roll it into a strip, you then wrap it around the top of trap to make a washer. this mait washer seals between the inside of the tray and trap. when youu tighten up trap any excess mait will be squeezed out and easly removed to use again. as mait is non setting it is easy to disconnect after. silcone provides just as good a seal and can be easly disconnected when set but its very messy and hard to completely remove from tray.


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## askew70 (2 Aug 2007)

kittycole said:


> Hi,
> I would use mait. Its not the threads that are leaking, its more likely to be where the trap sits on the tray. you use mait like mala and roll it into a strip, you then wrap it around the top of trap to make a washer. this mait washer seals between the inside of the tray and trap. when youu tighten up trap any excess mait will be squeezed out and easly removed to use again. as mait is non setting it is easy to disconnect after. silcone provides just as good a seal and can be easly disconnected when set but its very messy and hard to completely remove from tray.



I think you are right about the threads not being the problem, and you have made me realise that I may actually have two separate problems. 

I had been thinking that the portion of the waste that sits on top of the shower tray was my only problem, and that if I could seal between the bottom of this and the top of the tray that this would be all that I'd need. However, the seal between the underside of the tray and the portion of the trap that sits under there must also be inadequate as otherwise this should trap any water leaking from above. So, maybe it should never matter that water leaks from above so long as the lower portion of the trap is properly sealed against the underside of the shower tray?

I'll have to have a closer look from underneath the tray to figure out whether I can solve this without having to lift the floor to disconnect the waste pipe (so that I can seat the trap properly against the bottom of the tray). It may be that the trap was never fit snugly enough when the shower was installed and the current position of the waste pipe may make it impossible to achieve a snug fit without first disconnecting the pipe and probably shortening it (at the moment I have access only from a hole in the ceiling below but this doesn't allow me to disconnect the old trap from the waste pipe). I really hope it doesn't come to that.

Thanks to yourself and Leo for the advice.


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