Humidity Testing Kit

About Moisture Migration and Wall Sweating

Complex structures like buildings incorporate a number of porous materials like brick, plaster, mortar, timber and CONCRETE. All these materials hold some water within them. This water is mobile and can be transported into the atmosphere and into adjoining materials.

Key identification of moisture in concrete:

• Wet walls (could show as sweating walls or floors most noticeable during summer)
• Wet floors
• Humidity smell
• Black or green stains (Mold)
• Dark areas on concrete surface
• Moisture between items sitting on top of concrete surface
• Efflorescence (White powder on the floor or walls)
• Cold basement
• Cracks

Water may be present in a material in several different forms.

1. Firstly, there is free water, which in many cases can be removed from the material by physical separation.

2. Secondly, bound water, which can be present in a material. This is water that is required for chemical combination with the material, in the case of concrete for hydration and chemical absorption. Bound water forms a tighter bond between the water molecules and the solid material. This water is normally not measured and not accounted for in normal drying. Then there is also some water vapor held in the air within the pores of the material.

The migration of water from various pores of a material is by:
(a) Capillary action

(b) Water vapor diffusion.

It follows that a "wetter" material will have a higher water or water vapor content. The water vapor pressure will be higher and this will drive the water vapor towards areas where the water vapor pressure is lower (or less water is present) i.e. the inside of your basement or any surface indoors. In other words, water vapor will diffuse from a damp area into a dry area. (Most inside concrete surfaces are in warm or air condition environments therefore creating a dry ambient and becoming the catalyst for humidity absorption). This will continue until such time as equilibrium is achieved or until no further migration can take place.

Relationship between relative humidity and water vapor pressure.
Water molecules will migrate from areas of high water vapor pressure (or high relative humidity) towards areas of lower water vapor pressure (lower humidities). Knowledge of the dampness at all points of interest within a building is extremely valuable to a surveyor.

Why Moisture in Concrete is Important.
It is necessary to measure and reduce the amount of excess water in concrete after curing for a number of reasons:

1. To determine the time to dry the concrete sufficiently in order to apply a surface covering.

2. To reduce corrosion of reinforcing steel bars.

3. To reduce swelling and biological decay of wood based floor or wall coverings.

4. To prevent alkali attack on polymer based floor or wall adhesives.

5. To prevent mold producing environment

6. To avoid humidity smell

7. To predict the final mechanical and physical properties of the concrete.

8. To reduce the extent of alkali silica reaction and carbonation.

9. To study the drying out of various grades of concrete.

10. To understand the impact the humidity levels will have in the air conditioning system