Paul
wibbled on Sunday 27 December 2009 10:52

We are in the course of some fairly substantial building works. At the
start of November, we had some drains installed across the lounge
floor. Trenches were dug, drains installed, the trench filled with
shingle, and then concrete added on top of that to a depth of about
100mm below floor level. This was then blackjacked and another layer
of cement added to build it up to floor level.

Not knowing any better, we covered this with carpet, and a week ago
carpet layers were unable to lay a new carpet because it was
(unsurprisingly) too damp. Since then we have, of course, exposed it,
but it has not dried as quickly as expected.

If we have an ordinary fan play across it all night, it appears to
dry. But when the fan is removed, within 60 minutes it is damp again.
Oddly (or perhaps not), it is bone dry at the ends. Last night we
dried it with a hair drier, and the damp doesn't appear to have come
back so fast.

It is as if we can dry the top (say) 1mm, and then the damp comes back
from underneath.

If left to its own devices, how long will it take to dry please, and
how can we speed it up substantially please?

Many thanks,

Paul.

On top of what others have said, concrete dries out about 1" per week in
good warm summer conditions (jn a shady part of the house) by my observation
of watching 4" go off.

This time of year it may take a considerably longer time if drying is
unaided. Dehumidifier would probably be best bet.

Then establish if there is a damp problem due to poor or missing DPM
construction.

If so, I would simply insist the original builder fixes this.

I've had similar works done, where there was no substantive DPM in the house
in that area (it varies room by room in the limited areas where I have made
holes in the floor). Other places are blackjacked.

In one pair of rooms I finished with an SBR modified screed and that's seems
a good enough vapour block for my needs.

In another room where I wasn't rescreeding, I applied an epoxy 2 part DPM to
the surface of the screed (F Ball F75) then primed with Stopgap P131 and
finished with 3mm of Stopgap 300 HD levelling compound (required as the F75
is not a wearing layer). That worked.

It's not cheap but it's not that expensive for something that is
comparitively labour unintensive. You personally could do a 20m2 room single
handed with a little mental preparation. Laying 3mm of Stopgap 300 is a 1
person job for upto 5-10m2 and 2 person (just) for 20m2. It's another option
if digging holes in the floor isn't an option.


--
Tim Watts

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