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August 21 - August 25, 2017

How can it be determined if moisture within a CMU wall is causing repeated coating failure? If so, can the source of moisture entry be accurately identified for correction?

Selected Answers

From Zenith Czora of Durotech Industries, Inc. on August 22, 2017:
The source of moisture may come from different directions. First, you need to investigate whether the the moisture is being driven by air from inside to outside, if there is any leakage on the roof that went into the cavities of the wall, if moisture is coming from the ground due to inefficient damp courses or is it caused by wind-driven rain. If there is any leakage, it needs to be fixed; otherwise, there will be reoccurence of the problem. Moisture presence can be detected by the dampness and dark spots on the CMU wall .Using a reliable moisture meter for concrete, the reading should not exceed 5%. If it is exceeded, then there is a problem. Any presence of moisture within the CMU also drives the soluble salts out to surface that will cause adhesion failure, resulting in blistering and worse, film delamination. Improper surface preparation and poor primer/sealer quality will also lead to this coating failure. If the moisture is coming out from inside the room, provide sufficient ventilation in the room to minimize moisture build-up. Pre-treat surfaces and have a good sound surface preparation. Use a primer that is alkaline- and water-resistant but still allows the substrates to breathe. Use a topcoat that has a delicate balance between breathability and bulk water resistance. A good coating should pass  ASTM 6904 - resistance to wind driven rain.

From Trevor Neale of Blastco on August 22, 2017:
I lived for many years in a tropical area where buildings were constructed with cement parged cinder blocks and or a soft local stone many without damp courses of any type. Moisture was a constant challenge from the time in the mid 50s when latex/emulsion wall paints were introduced into the market place, prior to that lime wash and casein-based distempers, both porous, were the available wall coatings in very limited colours. Oil paints were strictly taboo due to saponification.. When latex finishes became available in the 60 and 70s we found the only way to offer clients a modern finish was to apply a new surface to the wall which was offset by studs to allow a space where the moisture pressure could be relieved, with small vents permitting air movements. Prior to that conclusion, we had tested very high-build epoxies without success. Basically, in a porous-substrate situation, unless it can be completely sealed during construction, we concluded it is virtually impossible to know the source of moisture. Good luck in your search!

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Tagged categories: Concrete; Concrete masonry units (CMU); Good Technical Practice; Moisture detection

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