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RE: Capillary Breaks

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I prefer the capillary break beneath the vapor retarder. Otherwise you create the potential for perched water which can exacerbate vapors.

If you put granular material on top of the vapor retarder it is for the purpose of equalizing moisture and minimizing the potential for differential curing and the curling that results. The material on top of the vapor retarder can have fines (unlike a capillary break). A capillary break is best done with 3/8" crushed rock. The crushed rock can be compacted, it holds in place, and it will break the capillary action. Avoid gravel which will roll around and does not compact.

Harold Sprague

From: GSKWY(--nospam--at)
Reply-To: <seaint(--nospam--at)>
To: seaint(--nospam--at)
Subject: Capillary Breaks
Date: Wed, 9 Feb 2005 13:28:04 EST

An article on the web site for a vapor retarder manufacturer said something
about putting a capillary break above the vapor retarder - the capillary break
being something like a layer of free draining gravel.

This is not the same as the endless ACI 302/360 discussion of a fill
layer/base course above or below the vapor retarder, it is somehow implying (I think)
that sufficient moisture might come up through the vapor retarder that you
need a capillary break on top of it.

I don't see how that can be true - I can see putting a capillary break below the vapor retarder, to prevent heaving right below the vapor retarder, but it
doesn't seem to make sense the other way around.

I asked the guy who wrote the article why anyone who do this,  and got this
as a reply:

"It has been our experience and that of many of the contractors we work with
that both ways work."

Does anyone have experience with a situation where it makes senses to put a
capillary layer above the vapor barrier?

Gail Kelley

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