Repairing internal concrete floor membrane

Hi,
sorry - it's another hypothetical question ;->
Re: "The Bungalow Project", we've evolved the new plan so that it works much better WRT to where new rooms will be and also WRT to logistics of doing the job.
The gotcha compromise is that one of the two bathrooms (well, the other is a bog and shower) has ended up landlocked behind a bedroom[1]. I'd have a toilet 1.2m away from the external wall.
So I need to bury a 110mm pipe under the floor and out through the wall. No general problem with any of this, simple straight run under a doorway, the drains outside are fairly deep and no issues with fall. Assuming that the wall footings are deep enough (out of the way, to be determined by digging hold outside) I have one problem to solve:
How do I repair the floor membrane after I've cut a trench about 300mm by 1.2m?
Here: http://www.diydoctor.org.uk/projects/constructiongroundfloor.htm
suggests I need to pour a load of "Structural Epoxy Pouring Grout" in, covering 150mm of the existing membrane on all sides of the cut and backfill with concrete then screed. Assuming I'd need at least 50mm of the epoxy, that's an absolute minimum of 16 litres which is coming in to 240 quit+VAT.
I'm aware that diydoctor are trying to sell their goods, so the question is:
Are there other acceptable ways to repair the membrane? I would have thought that, after dropping concrete around the pipe level with the existing membrane, that laying new membrane well overlapping the old, taping and pouring more concrete would have been sufficient. But I have no practical experience of DPCs...
Thanks for your thoughts :)
Cheers
Tim
[1] Bathroom being landlocked allows the bedrooms to have proper windows. Previous plans have severely reduced window area in one bedroom. I can live with electric lighting and forced ventilation in one of two bathrooms, but making a bedroom dark will be much worse.
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Tim S wrote:

You could get away with not digging any floors up if you used a saniflo.
Also, how do you know the existing floor has a membrane already in it? - they were only used from the late seventies onwards......saying that, I wouldn't worry too much about it, they are never completely sealed anyway and are often ripped and punctured several times during the concrete pour - 17st blokes wearing concrete encrusted wellies and pushing 5cwt barrows of concrete aren't very gentle WRT visqueen - it doesn't really matter, so long as you backfill and pack down as tightly as possible, then /try/ to get as much of the ground covered as possible prior to re-concreting
--
Phil L
RSRL Tipster Of The Year 2008
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Phil L coughed up some electrons that declared:

Hi Phil,
Valid suggestion, but after reading this group for n-years, I think I'd rather **** in a teacup than use a saniflo ;->

This is of course a very good point. Planning for the worst...

1950's here. That is interesting. No membrane would make the job a no brainer.

OK - seems reasonable. I knew they're not 100% watertight anyway, but I was talking to a welsh builder on my electrics course yesterday about it and he spooked me a bit. Just one of those things I am utterly clueless about (hence no common sense).
Cheers,
Tim
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anyway
pour
barrows
so
was
he
Not sure about 1950's, but our 1970's bungalow has a painted on bitumastic layer between the floor slab and the screed, which appears (from recent removal of internal walls) to be both intact and effective - screed appears totally dry everywhere I've been so far. If you do have a membrane of some sort between slab and screed you could consider dropping your new 110mm pipe to below slab level, concreting it in to match, and painting a bitumastic layer over the top. You may have to cut back your existing screed either side to produce a good overlap with whatever is there at present. Finally, new screed over the whole lot.
Success is likely to depend on your ground water levels and general dampness as much as anything else - we have well draining soil and a steep bank to one side of the house, which helps!
Best of luck with all this. Charles F
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Hi,
NO*SPAM coughed up some electrons that declared:

I was thinking to do something that, partly for the pipe's own good and partly if I;m going to break the dpc, I need to keep the pipe clear of it in order to have a decent chance of making it good (obviously excepting where the pipe comes out of the floor).

The info on bitumastic is ery interesting. I've used gunky bitumastic paint in the 70's so I know what you mean.

I think careful excavation of the first layer of screen is called for. Thanks for the tip - I hadn't considered the possibility that the dpc might be betwen the screen and slab, I was assuming it would always be under the slab.

Should be OK. The house is on a diagonal slope, so it's high on one side and low on the other. Might be water running past during rain but it should generally drain away. We're on clay, but there seems to be a reasonable depth of topsoil.

Thanks :)
Cheers
Tim
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Sorry if it's a stupid/granny sucking eggs question, but there's no way of taking the waste out through the bedroom and hiding it under a built-in wardrobe or something?
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snipped-for-privacy@mailbolt.com coughed up some electrons that declared:

Alas not easily. It would have to run back on itself around 4 walls :(
This bit is a real n-dimensional optimisation problem, in that we are splitting a medium room (former kitchen) into a small bedroom and bathroom.
The bathroom is small, but will 100% freedom on the placement of 2 new walls, it can be made to work extrememly well (ie it's not rectangular, but rather shaped to allow the bath and loo to be absorbed away from the central floor area, which makes a small space seem quite spacious).
The balancing act is not to make the bedroom useless, and again, it's been possible to end up with a non rectangular room that had no real dead space, takes standard single, or even a queen bed at a pinch and still has room to get around. This will be our daughter's room, so with a single bed, there's plenty of room for a table, wardrobe and a bit of floor for playing on.
The current and very knackered bathroom which was small and rectangular (ie no space left once the suite was wedged in) becomes a spacious extension to the hall, allowing it to house a piano or extra cupboards for "hall crap" (you know, stuff that doesn't belong anywhere but you always need)
I really must get a blog site up on this - just need to finish a computer upgrade cycle so I can get my antique webserver upgraded!
Cheers
Tim
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Tim S wrote:

Well two things spring to mind (if one ignores the possibility there is no DPM there in the first place!).
Usually when using sheet material DPM, the joins are simply overlapped by 350mm or so. Perhaps taped if the builder was feeling posh at the time. The other option is a painted on DPM - there are plenty of products to chose from here. Either approach would seem to solve your problem.
--
Cheers,

John.

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John Rumm coughed up some electrons that declared:

Thanks John. The job sounds perfectly feasible now :)
Cheers
Tim
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