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

In an earlier contribution to this discussion,
Lobster   wrote:


> 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


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.
-- 
Cheers,
Set Square
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Set Square wrote:

> In an earlier contribution to this discussion,
> Lobster   wrote:

>>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.

> 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?


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.)


> 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.


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

In an earlier contribution to this discussion,
Lobster   wrote:


> 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.)
>

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.


>
> 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 :-)
>

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!]
-- 
Cheers,
Set Square
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