Restoration of Damaged Housing

Effects of Water on Materials

Water coming into contact with building materials can degrade their functionality and value by a number of natural physical and chemical processes. Metallic corrosion is induced. Glues and other installed substances dissolve. Water destroys the attractiveness of materials by discoloration. Considering its absorptivity and fluidity, water is fairly dense; the loads it imposes can cause weakened structural systems to fail or sopping structural coverings to buckle. Contaminants carried by water can destroy materials that would be recoverable if saturated with potable water. If excessive moisture is not removed, then mold often develops in a few days and does further damage.

Prompt removal of excess water from materials and control of the humidity it generates by segregating the water from the unaffected part of the building will prevent a minor problem from wreaking widespread havoc in a structure. The wet portion is closed off to reduce or eliminate water and vapor migration beyond the portions of the building already damaged. That segregated part is called the drying chamber. For example, keeping the moisture content under 20% (kiln-dried lumber is often at 19%) usually prevents mold growth on wood. Selected chemicals in or on materials also eliminate or slow mold growth. Secondary material damage also results when building humidity becomes excessive.

The amount of water released in a structure varies from Class I through Class I V. Class refers to the quantity of water creating the damage, and higher class means the contractor expects evaporation of damp materials to take longer. For example, more dehumidification is required for Class III than for Class II losses. The degree of contamination of the water varies from potable water, Category I, to highly contaminated or black water, Category III. Contaminated water determines the amount of air filtration, protective measures, disinfection, and potential for effective material restoration.

Psychrometry

Psychrometry is the science of thermodynamics of moist air. The acronym, HAT—humidity, air movement, and temperature—composes much of the science. If air surrounding wet material surfaces exhibits a water vapor pressure that is lower than the pressure of water vapor from the material, then more water molecules will evaporate into the air than are captured by the material, and the material dries. The temperature and water content of the material have greater effect on internal water evaporation rates than does the air, although all impact the result.

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