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Applying Common Sense to Moisture Vapor Emissions and Moisture Content Test Requirements When Coating Below Grade Concrete Structures in Wastewater Applications

When establishing the minimum conditions suitable for coating concrete, many 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 and unrelated requisites. 

Product Number: 41216-989-SG
Author: R. A. Nixon
Publication Date: 2016
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When establishing the minimum conditions suitable for coating concrete, many 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 and unrelated requisites. This paper presents a discussion on the repeatability problems and margin of error concerns intrinsic to the most widely specified moisture related test standards especially when used for below grade structures. The author will further describe case histories which demonstrate the inaccuracy and unsubstantiated reliance on these commonly used test methods. These examples will be used to illustrate the many variables which influence moisture content and vapor emission 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 which establish some practical criterion for deciding when and where not to coat 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.

When establishing the minimum conditions suitable for coating concrete, many 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 and unrelated requisites. This paper presents a discussion on the repeatability problems and margin of error concerns intrinsic to the most widely specified moisture related test standards especially when used for below grade structures. The author will further describe case histories which demonstrate the inaccuracy and unsubstantiated reliance on these commonly used test methods. These examples will be used to illustrate the many variables which influence moisture content and vapor emission 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 which establish some practical criterion for deciding when and where not to coat 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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