Some people confuse humidity with moisture content. They assume that "dry air" means "dry" materials. Moisture content and humidity are really two separate, yet interrelated issues. Humidity relates only to the condition of the air. Moisture content generally refers to the moisture content of materials, usually expressed as a percentage of moisture content by weight. Yet both humidity and moisture content have a major impact on one another.

Hygroscopic materials are those which readily take up and absorb water vapor from the air mass. That is, they seek a moisture equilibrium with the environment. Most organic materials are Hygroscopic to some degree. Drywall, wood, paper, fabrics, some insulation materials and many other construction materials are Hygroscopic. As the humidity increases, they absorb water vapor, as the humidity decreases, they release water vapor.

Beware of Secondary Damage

Most indoor, organic construction materials are designed for "normal" humidity condition of 40% to 55% Rh. They can handle this humidity without deformation, delamination or mold damage. Yet every water damage situation is highly abnormal. A flooded environment may easily encounter 60% Rh for many days even weeks. These materials then seek an equilibrium with their environment, absorbing water vapor, potentially becoming damaged.

A balance drying system is when the rate of humidity reduction equals or exceeds the rate of evaporation. An inexperienced technician can actually increase the problem by loading the air with water vapor by using too many air movers without corresponding capacity for dehumidification. Proper humidity reduction is extremely important during the restoration process. In some cases these hygroscopic materials absorb water vapor far beyond their design limits, which results in secondary damage to hygroscopic materials. Common examples of secondary damage include humidity and or moisture damage to ceiling tiles, window frames, doors, cabinets, and condensation inside walls.

Monitor and Record Moisture Content and Humidity

In order to evaluate and control the drying process, and to determine when materials are properly dried, we must use methods of monitoring both the condition of the air and the moisture content of affected materials.

A variety of instruments are available for this purpose. These include electronic thermo-hygrometers and both penetration and non-destructive moisture meters. Thermo-hygrometers messure both the temperature and the relative humidity of the air. From these measurements we can determine the specific humidity of the air with a pyschrometric chart. A moisture meter determines moisture content levels and is used to monitor the rate of drying and evaluate when affected materials have reached their appropriate moisture levels. Both these measurements can be charted daily for additional understanding and supportive documentation can be provided with your invoice.

But let's not mistake the condition of the air with the moisture content of affected materials. Moisture content levels should be checked against a manufacturer's standards or against a non affected area. In lab tests, a control is often used to determine the normal. Our industry can establish a guideline by evaluating a material which has not been affected by moisture or humidity. Affected materials can then be compared with the
control percentage.

Don't Practice Old Medicine

A major restoration contractor asked me a very provocative question the other day.

"Do we really need to monitor humidity and moisture content on every job?" To formulate an honest answer I had to think back to when I started doing flood restoration almost 20 years ago.

In the 1970's, we didn't record humidity or moisture content readings. We really didn't have the knowledge or tools available.Yet,most customers were satisfied with our service. The customer, insured and insurer found the services acceptable, and we made a reasonable profit. Yet, hidden or unresolved damage may have been rampant without our knowledge. After all, we were carpet cleaners not "drying specialists". If problems developed, they just called a general contractor to replace the materials.