Vapor Barrier Under Concrete Slab On Grade

Aci 302 1 guide for concrete floor and slab construction states that the minimum thickness of an effective vapor barrier is 10 mils.

Vapor barrier under concrete slab on grade. We have a system that has worked well for us in the past. We would like to resolve the question of proper placement of vapor barriers under concrete slabs on grade. Thinner plastic can t stand up to the abuse of construction. That s why in most cases a vapor barrier should be installed under the slab.

This plastic sheet is in direct contact with the concrete as it should be in a rational world. However the far greater risk to a slab is long term curling over the lifetime of the concrete foundation which a high performance vapor barrier helps prevent. In nonproblem areas we have traditionally used 6 mil polyethylene film directly under concrete slabs and over a granular fill on the subgrade. It is important to use a concrete mixture with the lowest water content that will afford adequate workability.

Chemical and mineral admixtures are generally used to minimize the water content in a concrete mixture and provide adequate workability for placement. Pouring a slab on grade is a common way to lay a sturdy floor or foundation where a basement or crawlspace is unnecessary. Almost everywhere except california that slabs are placed on the ground a plastic sheet a vapor barrier is located directly under the concrete slab and on top of the ground photograph 1. Materials with higher perm numbers more permeable are classified as vapor retarders.

But they have also proven to be beneficial in reducing failures of moisture sensitive flooring materials adhesives and coatings caused by excessive emission of moisture vapor from concrete slabs. However concrete slabs are vulnerable to moisture from the ground. Without a vapor barrier moisture would continually wet the bottom of the slab as vapor will continuously drive from the high humidity below slab to the relatively low humidity above. A vapor barrier is any material with a u s.

Vapor barriers for slabs on grade. Vapor retarders are generally not necessary when placing exterior slabs on grade. Vapor barriers have been associated with certain concrete slab on grade problems including curling and cracking. Perm rating of less than 0 1 perm.