The Science Of Drying
Quite frequently we are asked how do we know how long it will take to dry a structure after it has sustained water damage. Our clients want to know that there is scientific research to back this up our estimates and that we are not simply pulling numbers out of thin air. The reality is that, yes, there is extensive and well-documented scientific research ranging over many years related to drying technology of various products. That research, and the subsequent industry guidelines which we follow, is conducted and produced by the Institute of Inspection, Cleaning and Restoration Certification (IICRC).
The IICRC was formed in 1972 as an independent, certification body that sets and promotes high standards and ethics within the inspection, cleaning, restoration and installation industry. The IICRC is regarded as the international industry standard to be used by restoration companies. All of our technicians are IICRC certified. When you hire us to do a job you can rest assured that our work will be completed in accordance with the industry’s “standard of care”.
So how do we determine what equipment to use and how long the drying process will take? Structural drying is a process that utilizes evaporation, the process by which water changes from its liquid phase to its gaseous phase. Evaporation is influenced by several factors:
- The level of moisture (i.e. relative humidity) in the air
- Water vapor pressure differential between the surface of the wet material and the surrounding environment
- Temperature of the wet material
- Air movement across the surface of the wet material
- Access to surfaces of wet materials
The application of air movement at the surface of wet materials is a critical component to the drying process. Evaporation is a surface phenomenon, and surfaces are measured in area (e.g. square feet). Therefore using linear feet of wall as the primary criterion for establishing air movement requirements is illogical.
- Drying is the process of removing excess moisture both at the surface and from within the materials and assemblies.
- The conditions conducive to effectively and efficiently drying at the surface of some materials and assemblies differ from the conditions conducive to effectively and efficiently moving excess moisture within the materials or assemblies.
- Rapid air movement across wet surfaces of materials or assemblies is a critical component of effectively and efficiently drying the surface of those materials and assemblies.
- Rapid air movement across the surface of materials becomes less important relative to vapor pressure as the focus of removing surface moisture gives way to reducing moisture content in low evaporation materials.
- Using the same criteria to establish air movement during the constant and the falling rate drying of materials and assemblies does not consider changing conditions.
- The linear foot formula for air movement of a room fails to consistently account for the actual surface area of wet materials and assemblies in different classes of water intrusion.
Humidity, airflow and temperature influence the movement of moisture within a material as well as the evaporation rate from the surface of material. These properties greatly impact the overall drying time for a project.
It is important to quickly control the moisture in the air and use sufficient airflow to dry the surfaces of materials to reduce water activity thus lowering the potential for microbial growth (mold). To ensure rapid, cost effective drying without secondary damage specific types and quantities of airmovers are recommended, depending on the type, porosity, location and square footage of the surface being dried. … The minimum quantity of airmovers recommended for various flooring surfaces are as follows:
- Non-porous and semi-porous flooring – at least one airmover per 400- 500 square feet is recommended. Give consideration to closets or small storage areas where airflow may be restricted.
- Direct-glue carpet installations – in installations where disengagement normally would damage or destroy carpet or cushion, at least one airmover is recommended per 300 square feet of carpet area, or one per room if smaller than 300 square feet. Give consideration to closets or small storage areas where airflow may be restricted.
- Stretch-in carpet – a minimum of one airmover is recommended per 300 square feet of carpet surface area, or one per room if smaller than 300 square feet. Give consideration to closets or small storage areas where airflow may be restricted.
As you can see there is a significant knowledge base which we pull from to ensure that we completely remove all excess moisture, both the visible standing water and the subsequent elevated levels of humidity, during our structural drying projects. If you would like to learn more about the science of structural drying and why we do what we do visit www.IICRC.org