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When can I seal the basement floor?

I have just finished building my retirement home with energy efficiency, green products and products made in USA. The Basement is a conditioned space and is heated with a 9000 btu Mitsubishi minisplit.
The basement has 6 inches of 3/4 stone tamped down with a 10 mil vapor barrier on top of the stone. The Vapor barrier is 10 mil and is taped all around to the basement wall with Stego tape and the seams are also taped. I have on top of this a 4 inc layer of polyiso rigid insulation withrflood5@gmaiaped and then the slab poured on top. The house is heated with 3 Mitsubishi 9000 btu minisplits and I have a ERV installed. The humidity in the house is a constant 40-45%.
I would like to seal the basement floor with a sealant or paint, the slab is 6 months old and we are in climate zone 5( Central PA). How long do I need to wait to seal the slab?

Thank you
Ron Flood
email: rvflood5@gmail.com

Asked by Ron Flood
Posted Dec 29, 2017 9:24 PM ET
Edited Dec 30, 2017 7:28 AM ET


1 Answer

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Using polyiso under the slab was a mistake, since polyiso can absorb moisture. The correct type of insulation to use under a basement slab is EPS or semi-rigid mineral wool. (XPS will also work, but green builders avoid the use of XPS because it is manufactured with a blowing agent that has a high global warming potential.)

I know that's water under the bridge, but I wanted to point out the error so that other GBA readers don't walk down your path. If the crushed stone layer under your polyiso is well drained, your faulty installation may work out OK.

If you are installing a concrete sealer on your slab, you should follow the installation instructions provided by the manufacturer of the sealer. One easy test is to tape a small square of polyethylene sheeting on an area of the slab and to leave the polyethylene in place for two or three days. If you see moisture beading up on the underside of the polyethylene, that's a sign that the slab needs to cure for a bit longer.

Answered by Martin Holladay
Posted Dec 30, 2017 7:27 AM ET

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