Monday, April 29, 2013


Vapor barriers are not suitable for waterproofing applications. As their name implies, they prevent transmission of water vapor through a substrate in contact with the soil. Typically used at slabs-on-grade conditions, they also are used in limited vertical applications.

Vapor barriers are sometimes used in conjunction with other waterproofing systems, where select areas of the building envelope are not subject to actual water penetration.

Vapor barriers are discussed only to present their differences and unsuitability for envelope waterproofing.

As previously discussed, soils have characteristic capillary action that allows the upward movement or migration of water vapor through the soil. Beginning as water and saturating the soil immediately adjacent to the water source, the capillary action ends as water vapor in the upper capillary capability limits of the soil.

Vapor barriers prevent upward capillary migration of vapor through soils from penetrating pores of concrete slabs. Without such protection, delamination of flooring materials, damage to structural components, paint peeling, mildew formation, and increased humidity in finished areas will occur. Vapor barriers can also prevent infiltration by alkaline salts into the concrete slab and flooring finish.

Vapor barriers are produced in PVC, combinations of reinforced waterproof paper with a polyvinyl coating, or polyethylene sheets (commonly referred to as  visquene).

Polyethylene sheets are available in both clear and black colors in thicknesses ranging from 5 to 10 mil. PVC materials are available in thickness ranging from 10 to 60 mil.

Typical properties of vapor barriers are summarized in Table 2.9.

Material Properties of Vapor Barriers

Vapor barriers are rolled or spread out over prepared and compacted soil, with joints lapped 6 in. Vapor barriers can be carried under, up, and over foundations to tie horizontal floor applications into vertical applications over walls. This is necessary to maintain the integrity of a building envelope.

Mastics are typically available from manufacturers for adhering materials to vertical substrates. In clay soil, where capillary action is excessive, laps should be sealed with a mastic for additional protection. Proper foundation drainage systems should be installed, as with all waterproofing systems.

Vapor barriers are installed directly over soil, which is not possible with most waterproofing systems. Protection layers or boards are not used to protect the barrier during reinforcement application or concrete placement.

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