Bricks, Masonry, Asphalt and Concrete - To poly or not to Poly?

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builderbob
05-03-06, 07:46 PM
I am pouring a slab on grade for a workshop that will be heated at times in the winter. Do I need to lay down 6 mil poly on top of the fill before I pour or leave it out?

Tscarborough
05-03-06, 07:57 PM
Yes, poly.
builderbob
05-03-06, 07:59 PM
Is this stricly to keep the concrete from sweating?

Tscarborough
05-03-06, 08:03 PM
It is to keep moisture from penetrating the slab from underneath.
Concretemasonry
05-03-06, 09:06 PM
As Tscarborough correctly pointed out, the poly is a vapor barrier that prevents the transmission of soil moiture through to the slab surface. It is negligible cost and does wonders.

"Sweating" is the condensation from the room air that occurs when the cold soil temperarures are transmitted through the concrete to cause condensation. This is normally not a problem where you have reasonable temperatures and decent soil temperatures.

By eliminating the vapor transmission with a vapor barrier, you are not adding to any possible moisture and you should not see moisture on the slab.

Dick