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Re: Slab on Grade Vapor Retarder Design

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There is a pretty good product out there called "Stego-Wrap" by Stego
industries, they have a good website and it is easy to install. It is
yellow, comes in 10 and 15 mil thicknesses, and is more robust than 6 mil
poly. We use it when either a vapor retarder or barrier is specified. It is
a good product that we, as a contractor, like because it is economical,
easily installed (comes in 10 or 15 foot wide rolls x 100 feet long) and
robust.

The fines layer over the top of a sheet used to be popular with designers
but drove contarctors nuts. It is very hard to place it, keep it in place on
top of  a sheet, and any mesh or bar supports bolluxed it. Just try
spreading a sheet of poly on your driveway and trying to place and keep 2
inches of sand on top uniform as you walk across it. Not pretty.

The rock stars of floors, like Kahlman Floors, suggest two layers of sheet
to mitigate shrinkage resistance. Others require holes to be drilled in the
rolls of poly to allow vapor to pass through; however, it is not much of a
barrier then.

Try a mix with the largest stone practical for placement (1-1/2 in top
gradation) and try a reasonable water cement ratio--less cement equals less
shrinkage, and there is a better chance that with more, bigger aggreagte and
even with reasonable w/c you'll see more complete hydration of water in the
mix. Low w/c results in dense concrete that may not fully hydrate all the
free water. The polycarboxylate admixtures are a great idea too.

The problem with these moisture issues is the concrete contractor has little
control over what happens after the slab is palced; if it is a rainy couple
of months before the building is closed in it may absorb more water than it
had after curing...........


Just an opinion.......

Richard W. Stone, P.E.
Project Executive
Technical Services/Project Management/Estimating
Concept Design/Engineering/Quality Assurance
 
Madison Concrete Construction Company
130 Quaker lane
Malvern, PA 19355-2479
email: rstone(--nospam--at)madisonconcrete.com
Voice:       610.695.8800
Facsimile: 610.695.8678
 
Nextel:      610.496.5764
 
 
Visit our webpage at  www.madisonconcrete.com  !!!!
 
 


 



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