Tricky one this. Four years ago I bought a 1970s dump and discovered that a damp patch (believed to be a leaking patio door) was actually a fractured water pipe. A copper 15mm elbow had split on its internal "corner?" on a buried hot water feed to a sink and was showing as a damp-to-wet area of floor. On further investigation, water had obviously saturated the sub-base and travelled along all heating channels rising in places to rot skirtings etc. I lifted all the plastic? tiles that had been bitumened over the ground floor and a film of water was found under most of them. As I say, that was four years ago and since then, all the upper surface of the ground floor slab appears to have dried out (sorry, forgot, solid concrete ground floor).
But, even now, I have discovered that if something impermiable is placed over the limit edge of the floor dpm where it rises to floor level (eg at all internal and external door thresholds), a damp film forms on its underside. This is true of a rubber backed doormat at the front door and a length of skirting which was being stored close to the rear patio door.
So the question is - how long should it take for the entire sub base to dry? Is it likely that this damp is coming from "outside" rather than "inside" the dpm IYSWIM? (ie it is general ground water rather than a leak)
This is causing concern for two reasons:
1. I am considering converting heating system to sealed and am concerned about possible leaks. 2. SWMBO was after wood floor in the dining room (with patio door) and I'm not sure whether I should consider this if there is a source of damp (however minor) beneath it.
Is it possible to locate minor leaks without actually digging up all the floor channels?
Thanks to anyone who's got this far.