FACTS ABOUT MOISTURE
MOISTURE RELATED FAILURES
The major culprits of moisture-related failures are fast-track building, developments initiated by the energy crisis, advances in building technology, and the spiraling costs of prime real estate. Buildings are built and occupied more quickly than ever. Since time is money, corners are cut. HVAC systems are not turned on until the premises are ready to be occupied. Concrete is not allowed to cure, and dry, and moisture membranes are not used, or are intentionally compromised.
To dry properly, each inch of concrete requires an additional month of drying time after the initial curing period of 28 days to one month. A seven-inch slab of concrete would need about eight months from the time of its initial pour. Curing compounds, sealers and climatic conditions can lengthen this dry time. Flooring materials placed on subfloors that are not dry enough to accept them generally fail two to six months after installation, especially if HVAC systems are not turned on until after the installation is complete.
Currently, the Anhydrous Calcium Chloride Test (ASTM Test Method F 1869-98) is the method most widely recommended by flooring manufacturers. This method requires test kits be placed randomly on the subfloor, with three test location s for areas up to 1,000 square feet, and an additional test for each 1,000 square feet. These test kits are left in place for 60-72 hours. The result obtained is the amount of water vapor, in pounds, emitted from a 1,000-square-foot area of concrete in a 24 hour period. The floor covering industry has recognized a dry concrete slab as having moisture vapor emission rate of 3 lb./24 hr./1,000 sq. ft., with some manufacturers allowing a higher emission rate for specific products. Contrary to popular belief, there is no established correlation between the Calcium Chloride Test and the electronic moisture test equipment currently available, including the hygrometer. Several other moisture testing methods are currently in use. Here is a description of how to interpret their readings:
1. VISQUEEN TEST - This standard ASTM method requires a sheet of Visqueen to be placed over the concrete surface for 24 hours. The tester looks for a change in color of the concrete or moisture condensing on the plastic sheet. While this method can identify moisture, it can also indicate that a floor is safe when it is not. Weaknesses of the test are the time required and the subjective nature of the visual observations. It is unreliable for use in the floorcovering industry, although some manufacturers consider it acceptable.
2. HYGROMETER - This method uses a hygrometer to measure the relative humidity of a concrete slab through internal or surface readings. Internal readings are the most accurate. relied on heavily in Europe, this test is just gaining acceptance in the United States. Recommendations should be obtained from the manufacturer of the flooring material used. Generally, internal readings of 80% relative humidity (as measured one inch or deeper into the concrete) are accepted as safe, and surface readings of 70% or less are generally accepted safe. This test, which takes 60-72 hours, is currently under consideration by the ASTM Resilient Flooring Committee, F06.
3. MAT-BOND TEST - This test was originally developed for linoleum installed with water-based adhesives. To perform the test, a piece of sheet vinyl, approximately 2' x 2', is placed face down into water-soluble or latex-based adhesive, while the adhesive is wet. The edges of vinyl are then taped around the perimeter to seal for 60-72 hours. when time is up, the material is lifted and checked. If the adhesive does not remove easily or shows substantial leg development, the concrete slab is considered appropriate for installation. One of the greatest problems with this test has been that, where VCT was to be installed, the test was done with a clear thin-spread or pressure sensitive adhesive, allowing it to dry and then placing the vinyl in it. Most adhesives on the market today are water-resistant; once dry, they will not break down or show any signs of moisture for two to six months or longer.
This method is used to identify if moisture is present, this test requires that the "mat" be placed into wet adhesive, regardless of the flooring to be installed.
4. ELECTRONIC INSTRUMENTS - There is no established correlation between any electronic moisture testing instruments and the Anhydrous Calcium Chloride Test. Some manufacturers have developed correlations between the hygrometer (relative humidity) and their instruments, but the accuracy and interpretation of these results should be questioned. These test methods and instruments have gained popularity because they are relatively fast and not very costly. However; their results are often misinterpreted. Most, if not all, require user experience. Once understood, the results gained from these tests can help the user to decide if additional tests are needed, using more accurate and acceptable methods. Some manufacturers have allowed the use of these instruments, listing he acceptable results.
5. TROXLER NUCLEAR INSTRUMENT - Although good for finding leakage and identifying soil and blacktop compaction, this instrument serves no purpose for the flooring industry.
It is very important for the tester to develop experience, no matter what testing method is used. The person responsible for testing must also make sure the surface tested is free of all curing compounds, sealers and coatings, which will provide incorrect results and void the test data.
Provide the test method and data to the general contractor, end user, or any other person who has final approval, as verification that you have taken the proper precautions and tested the subfloor to manufacturer recommendations. keep in mind that moisture test results only indicate the condition of the concrete at the time of the testing. A moisture membrane should be placed under the slab and maintained throughout the concrete pour.