Resists Vapor Transmission Controls Moisture

Vapor Transmission

Moisture vapor transmission rate is a measure of the passage of water vapor through a substance and the measure of its permeability. Water vapor transmission in concrete floors is simply liquid water that rises through the pores in the concrete by capillary action through a process called diffusion.

Hydrostatic pressure

Hydrostatic pressure is pressure created by standing or resting water (usually ground water surrounding a foundation) and concerns slab on grade and below grade concrete. The pressure is caused by moisture close to the bottom of the slab where a vapor barrier was not used allowing water to rise through the pores in the concrete. When enough water accumulates, it starts to exert pressure against the concrete foundation. This can result in a damp, musty smell, moldy odor, high humidity and water leakage.

Why is water damaging to concrete

Although concrete appears hard and strong, it is actually similar to a sponge with open pores and voids in which moisture can travel. Concrete is composed of thousands of microscopic pores that fill with water as concrete is being poured and set. Concrete starts to harden and moisture near the surface of the concrete slab begins evaporating and the tiny pores dry out. Once water has completely dried in a curing concrete floor, moisture vapor continues to diffuse through the slab from the adjacent soil’s moisture content. Small pathways created during the hydration process remain open and a pathway for moisture. If no vapor barrier exists between the soil and the concrete, moisture will build up. If a flooring was installed without a vapor barrier underneath, this moisture will cause it to buckle, delaminate and will fuse mold and mildew growth.