Condensation on clear plastic panels in my new workshop

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?

Reply to
John Irving
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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.

NT

Reply to
tabbypurr

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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)

Reply to
John Rumm

Concrete achieves maximum strength after 28 days, but it takes longer to dry out.. One month per each inch of thickness I believe, and that assumes a DPC was used.

Reply to
Andrew

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. Brian

Reply to
Brian Gaff

Assuming there is no heating yet, would the OP be wise to allow some ventilation by opening the windows?

Or install a dehumidifier.

Reply to
GB

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.

Reply to
ss

You could, but it sounds like it's dehumidifiying itself the free & slow way.

NT

Reply to
tabbypurr

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