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When establishing the minimum conditions suitable for coating concrete in wastewater applications, coating manufacturers, and hence specifying engineers and contractors, generally rely on unrealistic moisture content and moisture vapor emission rate requirements. These compulsory values are founded on laboratory testing rather than field experience, or worse still, on supposition rooted in unachievable, but conservative requisites. This paper presents a discussion on the repeatability problems and margin of error intrinsic to the most widely specified moisture related test standards. The author will further describe case histories that demonstrate the inaccuracy and unsubstantiated reliance on these commonly used test methods.
These examples will be used to illustrate the many variables that influence moisture content and vapor transmission rates and how the test results can be misleading. Successful coating performance and coating failures will be shown when the specified test requirements could not be achieved or were met respectively. The paper will close with some recommendations that establish some practical criterion for deciding when and where not to coat the concrete. The criteria proposed will include moisture testing value ranges, trends in the test data as well as consideration of the conditions to which the coated substrate will be exposed.
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