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Understanding Vapor Pressure

The Importance of Understanding Vapor Pressure

By Jocelyn Hare McLaughlin

Porous materials, like drywall, act like a sponge as water wicks up the walls. Moisture becomes bound within the materials, including wall cavities.

Baseboards and paint can act as a vapor barrier and slow drying. Airflow and dehumidification are necessary components of water restoration. Without airflow inside a wall cavity, vapor pressure builds up, preventing effective drying. The best way to promote airflow is through wall cavity drying. Wall cavity drying helps reduce the overall drying time of affected materials by speeding up evaporation.

By creating a hole in between each stud bay, the vapor pressure decreases, allowing the trapped moisture to wick out and evaporate into the drying chamber. (Capillary Action is the process of moisture pulling through the pores of affected materials and then evaporating.) Vapor diffusion occurs when water molecules move through a surface due to differences in vapor pressure. Vapor diffusion typically moves from high to low pressure.

With proper airflow and dehumidification, drying can now occur within the wall cavity.