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Re: Vapor barrier with void form?

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In a message dated 4/5/2005 12:28:16 PM Eastern Daylight Time, ShermanWC(--nospam--at)cdm.com writes:
I agree that painting the top of void form would be a waste of time.
However, one option we considered for a vapor barrier would be to place
the vapor barrier membrane over the top of the void forms - this would
permit the void form to deteriorate from the moisture below.
One question for the void form manufacturer might be whether it is moisture from the concrete or moisture from below that causes most of the deterioration of the void form.  They may have researched this, i.e. by looking at the deterioration over time.
 
The painting the top of the void form seemed like a bad idea all around.  It essentially does nothing more than hold the mix water in the bottom of the slab, increasing shrinkage and curling, etc. etc. 
 
A void form (unpainted) is actually a good curing environment.  It absorbs some of the excess mix water from the concrete,  but creates a moist environment against the bottom of the slab.
 
Gail Kelley