Types of Moisture Tests:
- Electric moisture meters have been available for several decades. However, they do not provide an absolutely accurate measure of the moisture condition of a concrete slab. Since most of the instruments are designed to read the upper 1 of a concrete slab the moisture condition deeper in the slab is not tested.
- The plastic sheet test, ASTM D4263, has been found to be unreliable because it depends upon temperature and dew point at the concretes surface. If the test is positive (dampness under the plastic sheet), then the floor is likely too damp and a water issue is present. However, a negative result under the plastic sheet (no moisture) does not necessarily indicate that the floor is dry.
- The calcium chloride test, ASTM F 1869-98, is used to measure moisture vapor emission rates (MVER) and was developed as a qualitative evaluation of floor moisture condition. These tests can also be unreliable producing both false high and low results dependent on temperature and humidity, water-cement ratio, use of lightweight aggregate and the presence of a curing compound.
- Relative Humidity (RH) tests give a much more useful picture of the actual moisture condition within the concrete regardless of mix, aggregate types, floor thickness or surface conditions. Relative humidity is important because the more moisture thats already in the air, the lower the rate at which water will evaporate and the less moisture that the air can hold. Relative humidity is a measure of the current amount of water vapor in the air relative to the total amount of water vapor that can exist in the air at its current temperature. (It is expressed as a percentage.) ?A relative humidity of 100% means the air cannot contain any more water vapor at that temperature, whereas a relative humidity of 50% means that the air only has only half as much water vapor as it can hold at the current temperature. An acceptable RH measure in concrete as specified by ASTM F710 is 75%. Relative Humidity tests can be purchased online.
Why reducing moisture in concrete is important:
It is necessary to measure and reduce the amount of excess water in concrete for a number of reasons including: ? The prevention of alkali attack, mold and mildew ? To avoid the smell of humidity ? To reduce the extent of ASR (alkali silica reaction) ? To reduce the corrosion of reinforcing steel bars ? To reduce the swelling or decay of floor coverings, paint, or a surface sealer.
Moisture enters concrete through the pores, or moisture is created by a difference in temperature. When the free lime found naturally occurring in concrete is mixed with excess Portland cement, a reaction occurs and forms Calcium Silicate Hydrate, also know as C-S-H. By preventatively sealing concrete with a Ghostshield concrete sealer a chemical reaction occurs and the pores of the concrete are filled with excess C-S-H. This process encapsulates moisture to create a permanent break in the capillaries of the concrete, stopping the passage of liquids and vapors. After sealing with a Ghostshield concrete sealer like Vapor-Tek 440, concrete will be permanently protected from water, moisture and humidity issues.
