Replacing DPM/Sealing Waste Pipe Questions.

[shaky1105]

I wonder if some of you guys would mind giving me some pointers on the best way to finish off the work I'm having to prepare for fitting my shower tray on a concrete floor please ? I've posted this in the Building Forum as it seems more apt than the Plumbers Forum and I've attached some pics to hopefully help explain what I'm on about:-



The narrow piece of channel (where the shower trap is temporarily placed) is newly cut by me. The rest of the channel to the right (albeit widened to expose the existing DPMso I can join onto that) is what existed and was completely loose (due to the old CH & water pipes being in that space, unwrapped and no DPM replaced !) so has been removed all around the house and reinstated with a newly attached DPM.

The issues I am not sure of are as follows:-

1. There seems to be two DPM's on this house (A 1980 detached bungalow) as you can see from the pic outside of the core drill exit. Is this normal for this age of bungalow ? I'm going to use a Pipesnug on the outside exit as I've done on the Bog outlet coz they look neat and my re-pointing/brick repair skills are limited to say the least - haha)

2. I know the internal DPM has to be turned up the wall on replacing it (I do that leaving loads of excess and trim it once the new concrete has cured) but what is the correct way to seal the shower waste pipe leading through the wall ? I'm getting a bit paranoid about any damp working it's way into the floor after doing a bit of the floor wrong in another part of the house and having to break it all up and start again, so I want to make sure this bit is done right coz it will basically all be under the new tray once finished.

3. Should the waste pipe be set into the concrete channel refill, or would I be better-off leaving it in an exposed narrow channel a tiny bit wider than the pipe itself ? This bit would help me a bit as well if it can be left "open" coz I'm not yet 100% certain of the final base level that the shower will be at so this would give me a bit of "wriggle-room" to adjust the height of the pipe to attach the tap onto the tray once it's in place. If it should be completely encased in the concrete, so be it. I'll just have to make sure I get the trap positioned accurately.

If it helps, the tray I'm fitting is an 1800 x 800 anthracite Mira Flight Level. Any tips or suggestions on any better way to do this (if I'm going about it all wrong - lol) would be gratefully received.

TIA

 

[shaky1105]

No-one ? Pretty please

 

[cdbe]

I doubt you will have any issues with damp from that small hole where the pipe goes through the wall, just just cut a neat hole through the membrane. A bit of "slack" to adjust the waste position is a good idea as long as you don't compromise the support for the tray - maybe trial fit the tray, get the waste right then fill in.

No idea why you have two DPC's (the ones in a wall are damp courses, the one under the floor is a membrane).

 

[shaky1105]

Thanks for the reply cdbe and also for spotting the typo re: DPM & DPC . All of the bungalows around here have the same double DPC, two courses apart, so I guess it was just how the developer did it at the time.

I was going to try to cut the hole in the new bit of DPM as accurate as I could anyway so it's good news that I should be Ok just doing that. I might just try to place some strips of DPM tape over the pipe/DPM joint just as a bit of a belt/braces backup as well. Re: the "slack" in the pipe, I was hoping that seeing as the tray can be mounted on legs (which will only be "spot" supports around the tray) and I'm gonna be fitting it directly on the concrete floor on a sand/cement mix, the max 2" (If I do create a channel for the waste pipe) slot of no support about 4" in from the edge of the tray and only just over half it's length wouldn't be a problem. I'm gonna get the pipe position as near as possible obviously but with the best will in the world, a bit of "give" would be useful .

I've already positioned the tray where its final position will be to be able to mark the cut-out in the floor for the trap so when it comes to final fitting, I should be fairly close as it is. It's just the finished height of where the trap outlet is, to marry up to the waste pipe that I'm trying to give myself a chance with.

Fingers crossed