How’s this for a dicey scenario: Arlene DiMarino is a homeowner with chemical sensitivities who lives a couple of blocks away from an EPA Superfund site.
“I am aware of a toxic plume of underground water that is close by,” she writes in a Q&A post. “I am concerned that these VOCs can permeate the cement floor and foundation.”
She plans to pour another layer of concrete over the existing basement slab. This will give her an opportunity to insert a vapor barrier to block any toxins from migrating into the house. But what’s the best product to use?
Alternatives to 6-mil poly
As GBA senior editor Martin Holladay points out, concrete itself is a good air barrier, as long as any cracks that develop are sealed with caulk.
But, he adds, it’s important to install a vapor barrier — typically 6-mil polyethylene with taped seams — under any concrete slab.
Other points of view are quick to emerge, like this flat statement from Robert Riversong: “I would never use standard 6-mil polyethylene under a concrete slab.”
Instead, Riversong recommends a product called Tu-Tuf, a robust, cross-laminated, 4-mm-thick plastic that’s advertised as free of pinholes. (It’s made by Sto-Cote Products and sold widely over the Internet.)
David Meiland suggests a product called Stego Wrap, which is 15 mils thick and said by the manufacturer to resist tears, splits, and punctures.
There’s also something called SlabShield, writes Andy Ault. SlabShield combines two layers of polyethylene and one of aluminum. The polyethylene sandwich protects the aluminum, a highly effective vapor barrier, from lime in the concrete. The manufacturer also claims that SlabShield provides a thermal break.
Ault says he used SlabShield on a Habitat for Humanity LEED Platinum project and was pleased with the result.