I've recently built a new workshop in the garden, 5m square. It has a concrete
floor that sits on plastic sheet to stop the damp rising. The walls are timber
framed and clad with shiplap that has been treated externally. There is a double
glazed french window and a double glazed single door. The roof is canted with an
eight inch drop front to back. The whole structure is silicone sealed and
weatherproofed. The roof itself is of corrugated Coroline sheet with a centre
section that is semi opaque plastic sheet. Good enough to let light in but not
completely clear. Condensation is building up badly on the plastic panels with a
small amount on the Coroline. As yet the walls are not insulated or lined and
the floor not yet fitted. The walls are to be clad with 150mm rockwool and the
floor with Kingspan blocks with 9mm Sterling board wall panelling and 13mm T & G
chipboard. The concrete was poured the second week in January so has been down
about seven weeks. I intend to insulate and board the ceiling sections that are
of Coroline with a centre section of clear 6mm sandwich type of plastic panel.
Problem is the condensation. Is there a likely cure or will things improve when
the walls and non-centre parts of the ceiling are insulated. I don't want to do
the ceiling insulation if the condensation is to persist. Does anyone have an
answer? Is the concrete cured? How long does that take? Will the floor benefit
from painting before I fit the bearers and insulation?
On Monday, 27 February 2017 21:14:04 UTC, John Irving wrote:
Concrete takes about a month to cure, and of course contains a whole lot of water that evaporates slowly.
I don't see a point painting the concrete, if as you said you already have a dpm. If there is no dpm then a waterproof finish can help a lot. But it's still drying out.
The thing is though that if you spend time in there you will get
condensation at any point where its colder outside than in. I'd suggest some
way to allow it to drain but also allow access just in case.
This newsgroup posting comes to you directly from...
Concrete screeds take a long time to fully dry out. I have seen
suggestions that traditional screeds generally dry at a rate of 1mm/day
for the first 40mm, and 0.5 mm thereafter after the screed has been
cured for 7 days - so you could easily have to wait 10 weeks or more to
get shot of most of the water depending on the screed thickness.
Adding the insulation will reduce the condensation if there is also some
heating (since warmer air will support more water content before it
precipitates out anyway, and the higher temperature of the internal
surfaces will make it harder for condensation to form in the first
place). Ideally you need to keep the temperature in there above the dew
point all the time. (I find with my (reasonably well insulated)
workshop, that setting a stat at 5 degrees is more than adequate to keep
it dry, and and tools rust free in there)
Apart from using the above I wonder if it can be eliminated completely.
From my shed door I have an extended corrugated plastic sheet roof,
garden fence one side and open on the 2 others, some mornings it is like
a shower underneath it and that is well ventilated being outside.
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