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RE: Slab on Grade Vapor Retarder Design

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RE p 15 Vapor Retarders: UnderSlabVaporBarrierPPP.pdf

Following is my recepie:

1.	Prepare the subgrade (smoother is better)
2. Place 3" of clean crushed over the subgrade, and compact. This serves as the the capillary break. 3. Place the vapor retarder (often called "barrier"). Use a product with ASTM E-1745 rating like Fortifiber Moistop Plus. Seal and flash all penetrations 4. Place a layer of crusher fines which will have a mixture of angular material and fines. It compacts very easily with a vibrating compactor. (My opinioin - This helps mitigate curling)
5.	Place REBAR for crack control.
6. Place the concrete with a low w/c ratio. Consider using polycarboxylate super plasticizer for workability and for earlier set.

Control Joints- This is a whole other topic, but use a SoffCut saw with the anti-ravel skid plate to force the slabs to be cut in time without raveling, and / or design your slab rebar crack control
with larger joint spacing.

A recently placed slab with low w/c ratio and polycarb super p provided a slab that had a very accelerated drop in moisture content allowing placement of the flooring.

Harold Sprague

From: "Nels Roselund" <njineer(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: Slab on Grade Vapor Retarder Design
Date: Mon, 8 May 2006 17:52:41 -0700

I need a reference for the design of a vapor retarder under a concrete slab
on grade.

I understand that a layer of sand over a plastic vapor retarder as
protection against construction traffic damage is no longer recommended due
to the tendency for the sand between the plastic vapor retarder and the slab
to become a reservoir for water that may damage a moisture sensitive floor
covering.  I understand that the current practice is to place the concrete
slab directly onto the vapor retarder.  What is the recommended appropriate
mil-weight for the traffic-resistant plastic sheet, or where can I find a
reference that provides guidance for selecting the appropriate plastic

Nels Roselund, SE
South San Gabriel, CA

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