On Sun, 27 Dec 2009 06:13:35 -0800 (PST), Paul
wrote:
Hi Bruce, thanks for your comprehensive reply.


You're welcome. I am sorry that I can offer very little comfort.


I have no reason to think the builder is incompetent, in fact as
builders go I think he is very competent.


If you have a competent, reputable builder, it is to be hoped that the
firm will want to retain their good reputation and put this work right
for you at no cost.


I also do not think there
was actually a DPC under the existing (very old) concrete floor.


I am surprised that neither you nor the builder have established this.


If rising damp was the problem, then we would be seeing signs of dampness
on the existing floor by now, I am sure. So I am reasonably confident
that we only need to wait until the 100mm of concrete dries (which it
has not been allowed to do), which is why I am trying to get an answer
to this question specifically. If and when it does not appear to be
drying properly, then we will have to look at what he has done.


Concrete fully cures (by hydration of the cement) typically in four to
six weeks. Only in conditions of extreme cold would it take any
longer. All the water that was in the original concrete mix reacts
chemically with the cement and, by the end of that period, the
concrete will not shed any moisture.

That means that any moisture you are seeing now is almost certainly
coming up from underneath, either from the ground or from leaks in the
pipes themselves.

There is another possibility, that the gravel surrounding the drain
pipes is acting as a conduit for water entering from outside the
house. Pipe surrounds using pea gravel can be very frustrating
because the gravel quickly transfers water from the smallest leak over
the whole length of any trench.

I recall one project where a pipe coupling failed and the only sign of
any leak was water gushing out of the pea gravel pipe surround some
300 metres away. It took a lot of excavating to find the leak, which
was massive, with the pipe being 600 mm in diameter, running at 4 bar
pressure and unable to be turned off for more than a couple of hours.
That's all the time the repair took to complete, but it took several
days to locate the leak. :-(