Burying waste pipe in floor screed - damp membrane??

[Lobster]

I'm laying a new concrete kitchen floor shortly, and need to bury a 1.5" waste pipe throught/beneath it. (This is because the sink will be on the wrong side of an internal doorway, and there's no other route to the gully outside).

The pipe will run through the screed, with suitable fall on it, and emerge at the outside wall about 1.5" above the outside ground level, and will be about 2-3" below the floor level and DPC on the inside; so it will enter the house above the Kingspan insulation and polythene dampproof membrane I'll be installing.

Question - I'll obviously need to penetrate the membrane with the waste pipe, but how do I do that without compromising its dampproofness? Presumably there must be a recognised method, as what I'm doing isn't particularly unusual.

Thanks David

[Set Square]

It will presumably penetrate a vertical bit of membrane where it is turned up against the wall? If so, can't you cut a hole in the membrane and seal round it with mastic?

Whatever you do, I would recommend setting a *larger* pipe into the screed, and then having the actual waste pipe running through the inside of it. It will aid maintenance no end! I did precisely that when converting the back end of the garage into a utility room. The washing machine waste had to be taken out under the floor. I set a length of 3" (I think) pipe into the screed (which was 6" deep - so plenty of fall) and put some shuttering about

6" square right in the corner where the washing machine stack pipe was going. There is thus a 6" square area with no screed in the corner, for accessing the end of the buried pipe.

[Lobster]

Mm, that's kind of what I'd been thinking of, just not convinced of the integrity of the joint with pipes and polythene flapping about, and little scope for overlapping the two to give a reasonable size of interface. Plus this is outdoors and exposed, so I'm going to have to assemble the DP membrane, kingspan and lay the screed all in one day (ie can't leave it overnight for mastic to set nicely before laying the screed.)

Nice, I like the idea of shuttering off the area where the pipe emerges; I was a bit worried about burying a 90-deg bend in the concrete! But given that this will give me access to both ends of a continuous length of 1.5" pipe, personally I think it'd be overkill to use the larger pipe too. Famous last words :-)

Thanks a lot David

[Set Square]

In that case, try to cut a round hole in the membrane - just big enough for the pipe to pass through - and then stick the membrane to the pipe with Gaffa Tape.

My rationale for sleeving it was that the whole pipe could be taken out and unblocked if necessary - or even replaced. Having said that, that was in

1989, and I haven't had to take it out yet! [Bet I will, now!]