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RE: Vapor barrier with void form?

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This sounds like the age old Colorado expansive soil problem with VCT flooring material adhering to a concrete slab. The problem is adhesion and potential delaminating bubbles in the VCT covering.

You may also want to explore the topically applied epoxy materials that are placed on top of the concrete slab. With the epoxies, the moisture content of the slab is not as big of a problem. Time delays waiting for the slab moisture to come down are a big problem.

Curing time and the moisture migration after curing is complete will also be a problem with the concrete itself no matter where the vapor retarder is placed. I would suggest that you explore the topically applied epoxies.

I like to hold a pre-construction meeting with all of the people in the same room to express methods and concerns. The concrete supplier, finisher, pumper, VCT manufacturer, VCT installer, Owner, GC, architect and engineer should all attend. It saves a lot of finger pointing later.

Harold Sprague

From: "Sherman, William" <ShermanWC(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: RE: Vapor barrier with void form?
Date: Tue, 5 Apr 2005 12:27:48 -0400

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.

The membrane could be taped at the joints, but there still would be some
question as to how effective it would be after the void forms collapse.
This also would require the vapor barrier to be in contact with the
bottom of the concrete slab, as placing granular material above the
vapor barrier and void form does not seem practical. Thus, this is not a
great solution.

Another alternative we are considering is a sealer applied on top of the
concrete (below the tile floor finish), in lieu of a vapor barrier below
the concrete slab. We will discuss this option further with the tile

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)

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