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RE: Vapor Barriers for Wood

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I would strongly discourage using aluminum in contact with concrete as the 
two result in a bad marriage.  The reaction between the two will cause 
hydrogen gas to develop in the concrete, causing the concrete to expand.

Aluminum used to be used in expansive grout, until it was recognized that its 
behavior is unpredictable and damaging.

The poor history of aluminum and concrete is the reason that aluminum 
conduits are prohibited from being embedded in concrete and the reason that 
we specify non-metallic expansive grout.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Albert Meyer wrote:

I have seen a major developer we design for typically wrap the end of
the beam with continuous aluminum flashing (termite shield) and then
grouting the pocket solid around the aluminum.  My concern with this is
that I see the potential for moisture to condense on the surface of the
metal in humid conditions since the metal flashing is in direct contact
with the concrete and generally remains cool.  It would seem that this
detail may draw moisture to the end of the beam at the pocket.  I know
that there typically is no attachment of the beam to the wall, so the
wrapped and grouted detail would seem to provide more support for
lateral loads than the air gap detail.  I know this doesn't completely
answer the question, but I hope it helps a little.

Albert J. Meyer, Jr., P.E.<<