Unbelievable an *on topic* thread:-)
Is there a time limit between laying oversite concrete and fitting the insulation, dpc and screed?
Concrete drying time must be similar to screed and there are lots of warnings about that. Does it matter if the insulation foil is in contact with moist concrete?
Logic would suggest that if you have a DPM below the concrete then the only way out for the moisture is through the top surface. I believe curing time for concrete is 28 days.
I have not consulted this site in a while but checking it out may definitively answer your question;
Is the OP talking about 'drying' or 'curing'? If it dries out too quickly it won't be able to cure properly; on the other hand nearly all concrete is made with more than enough water to make it workable, and the excess water will need to dry out eventually, depending on where it is.
With ordinary cement 28 days is the 'official' curing time, i.e. nearly all strength is achieved by then.
It is a *sequencing* issue.
I am constructing a corridor linking an extension to a now cut off garage. Planning and Building Control kindly allowed the garage to be used domestically subject to the usual insulation requirements. For future proofing, the link also needs to meet the regs. hence underfloor insulation.
It would be convenient to finish the floor before the structure is weatherproof and before serious frosts arrive.
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I always thought proper drying time was a month per inch of concrete, i.e. longer than you expect.
You can put a secondary dpc on top of the slab.
where then would the moisture go? (I thought that was why DPM above the slab was an /alternative/ to DPM below it.)
Doesnt need to go anywhere. Concrete sort of meeds CO2 to set tho, so its not great hermetically sealed
(I thought that was why DPM above the
Umm. I thought CO2 absorbtion by concrete was an issue for steel reinforcement rather than a necessary part of the cure.
I put plastic sheet below the concrete to save properly blinding the hardcore and will put dpm over the insulation.
I can re-plan the work and tarpaulin over the roof to create a tent.
No it doesn't. That's lime mortar. Portland cement sets if sealed or underwater. There's just the issue of whether the excess water in the mix could cause a problem.
Concrete doesn't set by "drying" (it will set underwater.) A non-linear chemical reaction takes place. You need to wet concrete down as is sets.
Chemicals in wet concrete will attack aluminium foil (strongly alkaline). You can buy a plastic film to put down to separate the two.
Would not a dpm just under the slab tend to wear out rather fast letting all those problems reoccur? Brian
If done properly the oversite is stable, is topped with compacted crushed stone or the like, and blinded with fines. So there's nothing to move which could "wear out" the DPM.
From the little I see of ground work around here I can see why some prefer block and beam ;)
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