concrete MOISTURE TESTING
A certain amount of water is needed for a contractor to mix, place and finish a concrete floor slab, depending on mix design, and a proportion of that water must remain in the concrete for curing, or “hydration". The remainder of this moisture, usually about 50% of the original “mix-water”, will eventually leave the concrete slab through evaporation, during drying. New concrete requires 28 days to cure, and at least 3-4 months for excess moisture to evaporate, although drying can take up to one year, depending on the thickness of the concrete.
If a floor covering, coating or other topping is installed on a concrete floor slab before this time, or additional moisture is inadvertently introduced to the slab, this excess moisture will be trapped below the surface and may cause problems for the flooring, including staining and discoloration; adhesive failure; bubbles or blisters; warping; and de-bonding or "delamination". Trapped, excess moisture may also cause degradation of the concrete through the processes of efflorescence, carbonation, alkali-silica reactivity, or sulfate attack.
In the case of acid-stained concrete, and other types of decorative concrete flooring, wet or damp areas of concrete may cause the color on the surface to lighten - by diluting it - or to darken significantly - through prolonged reactivity of the product or intensified curing of the concrete. Either way, the color effects on the floor are unpredictable, and these areas will usually stand out from the rest of the floor. Sometimes, excess moisture will even prevent a stain, dye, overlay or sealer from setting up, and drying, or cause the material to "delaminate", that is, come up in sections, shortly after installation.
Whether new or existing concrete has a moisture problem is not always obvious, or even apparent. The problem may only manifest itself after a flooring system has been installed. Even though the concrete floor slab in question may already have had plenty of time to cure and dry, outside sources of additional moisture can be easily introduced to the concrete through adverse weather conditions; a high water table; standing water; osmosis; subgrade moisture vapor; landscape irrigation; pipes and drains; gutters and downspouts; spill; and routine cleaning & maintenance. Because a concrete slab acts exactly like a sponge, this excess moisture may just disappear internally with no visible exterior sign.
Therefore, every concrete floor slab needs to be tested for moisture content before decorative concrete flooring is installed. Almost all acid-stained and decorative concrete flooring product manufacturers specify this in their technical data sheets (TDS). Such testing includes both moisture content and moisture vapor transmission and may be done through a variety of methods outlined by ASTM International. Unfortunately, most contractors do not have the training and equipment to do so, or believe it is even necessary. Premier Veneers tests the underlying concrete for moisture before every flooring project. We use the Concrete Moisture Encounter (CMEX II) from Tramex, and we are certified in concrete moisture testing by the International Concrete Repair Institute (ICRI). We are one of only 2 such certified contractors in the entire State of Michigan. (See our listing here.)
At the outset, testing involves measuring the concrete surface (to a 3/4” depth) with an electronic meter to determine whether moisture content levels are within normal range. This procedure can be done quickly and may take only 10-15 minutes depending on the size of the floor. If anomalies are apparent, then further testing of the concrete can be done in those areas to measure the relative humidity of the interior of the concrete (2-3” from the surface). This testing takes several hours over a 24-hour time frame, and quantifies the extent of a moisture problem so that an appropriate remedy can be pursued. If excess moisture does not have an identifiable cause, dehumidification equipment can help dry out the concrete to acceptable levels. "Moisture barrier" primer coatings may also be installed to block any excess moisture from affecting a flooring installation. Premier Veneers uses an industrial grade dehumidifier from Dri-Eaz during acid-stained and other decorative concrete flooring projects to expedite drying.
Whether you are having decorative concrete flooring installed, or some other type of floor covering, Premier Veneers can test the moisture content of your concrete slab. We routinely test basement floors for moisture following clean-up from flooding damage. This helps homeowners know if their concrete floor has sufficiently dried, or about how long that might take. Restoration contractors are not trained, let alone certified, to do so. By contrast, not only will our testing reliably tell you exactly how much moisture is in your concrete, but those results once documented will stand up in court, if need be.