Removing Moisture from Materials
The rate at which moisture moves through materials depends upon two primary factors: the type of material affected and the degree of wetness. The type of material affected will vary in permeability (ability for water to pass through the material), hygroscopicity (ability to absorb water), thickness, density, temperature and "R" factor (resistance to heat transfer).
Each of these characteristics will influence the way in which water travel through the material. The degree of wetness will influence the moisture movement, in combination with other material characteristics, by indicating the type of water being addressed. Water will be present in one, two or three forms:
- Surface Water
- Free Water
- Bound Water
Surface water is readily available at the surface of a material. It is liquid, visible and will evaporate readily. All materials are capable of supporting surface water. Surface water is best removed physically using mechanical extraction equipment or other physical means. Minute amounts of remaining surface water are readily evaporated using large amounts of airflow and moderate temperature and humidity.
Free water is present within a material but is not bonded. It exists in cavities, open pores and other air spaces within the material. It is liquid, generally visible by a darkening of the material (e.g., wood) and can evaporate readily. Most materials are capable of supporting (containing) free water. Materials not capable of retaining measurable amounts of free water are non-permeable, non-porous materials such as vinyl, vinyl composite, steel, rubber and some other solid, synthetic materials.
Bound water is absorbed by the material and held captive by chemical bonds. It is similar to vapor in that it is not fluid, yet similar to a solid/liquid in that it is bonded to other molecules. Because it is bound to other molecules, it must first be freed before it can be removed.