Problem Solving Forum
December 9 - December 13, 2019
What is the best method of testing for moisture content in concrete masonry unit (CMU) walls before application of coatings?
Zenith Czora of Durotech Industries, Inc. on
December 11, 2019:
Moisture content in CMU walls can be checked by th ...read more Moisture content in CMU walls can be checked by the plastic sheet method: ASTM D426383- Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method. This method is a qualitative test and does not really measure moisture content but shows evidence of moisture and whether the moisture is moving toward the wall, in which case the CMU wall is typically ready for coating application. This test involves covering the surface of the CMU wall with impermeable material such as a plastic sheet. A 460•460 mm square of 0.1mm thick plastic sheet is placed on the CMU wall surface and sealed around the edges with tape. After 16 to 24 hours, the sheet is removed and the area is inspected for moisture or color darkening. Color darkening occurs in some instances when the moisture movement is slow and there is still a slight dampness on the surface. To measure quantitatively, use a moisture meters designed for concrete like Tramex impedance moisture meter. Through an electrical impedance test, moisture content is measured by generating a low frequency electric field between electrodes at the bottom of the instrument. Depending on the moisture content, the measurements are made to a depth of several centimeters. The concrete wall is deemed dry enough to coat when the moisture content is not more than 5.5%.