Moisture in concrete and coatings sensitive to damp.

Slabs of concrete are the system most used in the construction of all types of buildings and the use of concrete walls is ever more common. Sometimes the concrete surface may be left as a decorative feature in itself, while on other occasions it may be decided to cover it with coatings and finishes.  

For the correct application of coatings sensitive to damp (including adhesives) an understanding is required of the source of the moisture within the concrete, the variations in damp during drying time, the factors which affect drying and the drying point after which coatings sensitive to damp may be applied.  
We will go on to present a brief summary of how to determine the moisture content in concrete and how to interpret the information in order to obtain a realistic indication of whether the concrete drying point is suitable for applying the finishes. 

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The total degree of moisture within the concrete, whether water or water vapour, is known as the “moisture content” and is generally expressed as a percentage of the mass of the concrete.    

Moisture may exist in the form of water (when the concrete is damp and the pores are saturated) or as water vapour. The amount of water vapour, and thereby the relative moisture within the concrete, varies significantly with time, depending on the degree of water vapour which entering or escaping from the concrete. 

It is important to bear in mind that due to the minuscule capillaries of concrete, it may be almost saturated with water and yet have a moisture content of just 5%.  This has implications for what is considered a “sufficiently dry” concrete surface.