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. 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?
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 :)
 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.