Dampness
Concrete Moisture and Dampness Problems: How can testing help?
Accurately assessing the moisture content of a concrete slab is crucial to ensure the success of any subsequent flooring or coating installation. However, no single test can provide a complete picture of the moisture condition of a concrete slab.
The most commonly used test methods include the calcium chloride test, relative humidity test, and moisture content test. Each test method has its advantages and disadvantages, and the results of one test may not be enough to make an informed decision about the suitability of the slab for the installation of flooring or coatings.
Therefore, it is essential to perform multiple tests and analyze the results in conjunction with other relevant factors, such as the concrete mix design, age of the concrete, and environmental conditions, to determine the best course of action. A comprehensive evaluation will minimize the risk of moisture-related issues and ensure the long-term performance of the flooring or coating system. We consider each method in the article below and offer our conclusion on the best test method for assessing concrete dampness.
What happens when concrete becomes damp?
When moisture becomes trapped in concrete floors due to issues with building services, such as plumbing or underfloor heating, flooding, fire suppression, failure of a damp proof membrane, or design and construction flaws, it can have severe consequences for the occupants of the building, the building itself, its services, finishes, contents, and collections.
Excess moisture can cause a range of problems, including bubbling, blistering, and delamination of floor coverings, as well as dampness at the base of walls and skirting. Furthermore, when an impermeable floor covering traps moisture in the slab, it can lead to mold infestation, which can cause health issues and further damage to the building. As a result, it is crucial to ensure that proper measures are taken to prevent and address moisture-related problems in concrete floors.
qualitative Test for Concrete Dampness (ASTM D4263 concrete moisture test)
This test method requires the application of an 18-inch (460mm) square of polyethylene film onto a concrete slab, followed by a minimum of 16 hours of waiting time. The underside of the sheet is then inspected for indications of moisture. If moisture condensation or darkening of the concrete color is observed underneath the sheet, it indicates the presence of excessive moisture, and the slab is deemed unsuitable for moisture-sensitive floor coverings.
The issue with the ASTM D4263 test lies in the potentially misleading nature of its results. If moisture is visible under the plastic sheet, the test confirms that the concrete slab is too damp for installing flooring. However, the opposite is not always true. A negative test result, which involves a dry plastic sheet with no visible moisture, does not necessarily guarantee that the slab is adequately dry for installation purposes.
Quantitative Test for Concrete Dampness (ASTM F2170 Relative humidity)
While there are several moisture testing methods available, not all are created equal. One of the most reliable and accurate methods is the ASTM F2170 in situ relative humidity (RH) test. This test measures moisture levels within the slab, rather than just at the surface, providing a more accurate picture of the overall moisture condition.
One of the major advantages of the ASTM F2170 test is that it provides hard numbers expressed as a percentage of relative humidity (RH). These numbers make it much easier to determine when the slab is dry enough for installing the finished floor, helping to prevent moisture-related issues down the line.
When it comes to ensuring the success of a flooring or finish installation, taking a comprehensive approach to moisture testing is essential. The ASTM F2170 in situ relative humidity test is a proven and reliable method for accurately assessing the moisture condition of a concrete slab, making it an invaluable tool for any construction project.
Moisture Vapor Test for Concrete Dampness (ASTM F1869)
The calcium chloride test method is a commonly used technique for determining the moisture vapor emission rate (MVER) from a concrete slab.
To perform the calcium chloride test, a small dish of calcium chloride is sealed on a clean section of concrete under a plastic dome. The salt absorbs moisture from the environment, including any moisture coming from the concrete slab. After three days, the weight gain of the calcium chloride dish is used to calculate the MVER.
While the calcium chloride test method is still specified by many flooring manufacturers, architects, and adhesive manufacturers, it only tests the surface conditions of the slab. This can be problematic because moisture levels can vary significantly within the concrete slab, and the test may not accurately reflect the overall moisture condition.
It's worth noting that the calcium chloride test method has been disallowed as an appropriate method for testing on lightweight concrete. This is because the test does not account for the different properties of lightweight concrete, which can result in inaccurate moisture readings.
When it comes to moisture testing for concrete slabs, taking a comprehensive approach that includes testing moisture levels within the slab is essential. While the calcium chloride test can be a useful tool for assessing surface conditions, it should not be relied upon as the sole method for determining the moisture condition of a concrete slab.
Which Test Method is Best for Measuring Concrete Dampness?
In conclusion, accurately assessing the moisture condition of a concrete slab is crucial to avoid issues with flooring and finish installations. While the calcium chloride test method is commonly used, it only tests the surface conditions of the slab and may not provide an accurate overall picture.
To get a comprehensive understanding of the moisture conditions within the slab, relative humidity testing using in situ probes is the most reliable and accurate method. This involves drilling test holes into the slab and placing a small probe into the hole to equilibrate with the slab before taking readings.
Research has shown that placing the probe internally, at a depth of 40% of the slab’s total thickness, provides the best indicator of the moisture conditions that the adhesive and finished flooring product would encounter if installed. By using the relative humidity test method, it's possible to get hard numbers expressed as percent RH, making it easy to decide when the slab is dry enough for installation. Overall, using this method can help prevent moisture-related issues and ensure the longevity of flooring and finish installations.