concrete MOISTURE TESTING
A certain amount of water is needed in order 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". This is usually referred to as the “water-cement ratio”. The remainder of this moisture, usually about 50% of the original mix-water, will eventually leave the concrete slab through evaporation, during the drying process. 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. Effective drying of an indoor concrete slab will usually not begin until the temperature and relative humidity of the air inside the building has been established at normal service conditions.
If a floor covering, coating or other concrete topping is installed on an interior floor slab, or exterior flatwork, before this time, or additional moisture is inadvertently introduced to the slab, such as from rain, sprinklers, or even the curing process, this excess moisture can become trapped below the surface and cause problems for the flooring, including mold; indelible staining and discoloration; adhesive failure or degradation; bubbles and blisters; warping and deformities; and de-bonding or "delamination". Trapped, excess moisture may also cause deterioration of the concrete itself, such as pitting, spalling, and scaling, through different natural processes like efflorescence, carbonation, alkali-silica reactivity, and sulfate attack.
In the case of decorative concrete flooring, for example, acid-stained concrete, wet or damp areas of concrete may cause the color of the surface to lighten, by diluting the coloring media; or to darken significantly, by acting as a catalyst, and prolonging the reactivity of the product, or intensifying the curing of the concrete. Either way, the color effects on the floor can be completely unpredictable, and as such, these areas will usually stand out from the rest of the floor. Sometimes, excess moisture may even prevent a concrete stain, dye, overlay, sealer or coating from setting up in the first place, and subsequently drying; or it may cause the material to "delaminate" from the floor, or come up in large sections, shortly after installation.
Complicating this whole scenario, and due to the overall depth of the concrete (usually 4” or 6”) it may not always be obvious, or even apparent, that new or existing concrete has a moisture problem. A moisture problem may only manifest itself after a flooring system has been installed, and effectively blocked that moisture in the concrete. This is because, even though the concrete floor slab in question may have already had plenty of time to cure and dry, outside sources of additional moisture are easily introduced to the concrete through: adverse weather conditions; a high water table in the soil; standing water; chemical osmosis; subgrade moisture vapor; landscape irrigation; breaks or leaks from pipes and drains; overflows from gutters and downspouts; spills; and even the water used in routine cleaning & maintenance. Because a concrete slab is similar to in composition, and acts like, a sponge, this excess moisture may just disappear internally for long periods of time, with no visible exterior manifestation.
Consequently, it is imperative that every concrete floor slab, or section of exterior concrete flatwork, be tested for moisture content before any type of decorative concrete flooring, like acid stain, or spray texture cement overlays, are installed. Almost all acid-stained and decorative concrete flooring product manufacturers specify such testing, as a requirement, in their technical data sheets (TDS), in order for the product warranty to be honored. Such moisture testing often includes both “moisture content” and “moisture vapor transmission”, and may be done through a variety of methods, which are outlined by the American Society for Testing Materials, or ASTM International. Unfortunately, most contractors do not take the time or have the training and equipment to do so; most even believe it is not really necessary. We at Premier Veneers test the underlying concrete in a home or building project space for moisture before every flooring project. We use the Concrete Moisture Encounter (CMEX II) from Tramex to do so, and we have been certified in concrete moisture testing procedures 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.)
The first stage of concrete moisture testing involves measuring the surface, to approximately a 3/4” depth, with an electronic impedance meter to determine whether moisture content percentage levels are within a normal range, which usually means below 5%. This procedure can be done quickly by a trained and certified contractor, and may only take 10-15 minutes for an entire floor to be done. If multiple reading anomalies become apparent, then further testing of the floor slab can then be done in those areas to measure what is referred to as the “relative humidity” of the interior of the concrete, which normally means 2-3” down from the surface. This testing will usually take several hours, over a 24-hour time interval, and will quantify the exact extent of any moisture problem so that an appropriate remedy can be pursued before installing flooring. If excess moisture does not have an identifiable cause, industrial dehumidification equipment may help dry out the concrete to normal levels within an acceptable time frame. Another effective option is a "moisture barrier primer coating”, which after being rolled onto the concrete surface, will block any excess moisture from subsequently affecting a flooring installation. Premier Veneers uses a state-of-the-art, industrial grade dehumidifier from Dri-Eaz, called the LGR 700XLi, before and during acid-stained, and other decorative concrete flooring, projects to expedite drying.
Whether you, as a homeowner or business owner, are having decorative concrete flooring installed, or any other type of floor covering, Premier Veneers can test the moisture content of your concrete slab - whether we are doing the actual flooring installation or not. We routinely test basement floors for moisture following clean-up from flooding damage. We also are called in to perform testing of damp or wet basements shortly after the construction of new homes, or remodeling of existing ones. Our testing helps homeowners know the extent of any moisture problem they may have, and if and when their concrete floor has sufficiently dried out, or about how long that process might take. We find that flood, fire and emergency restoration contractors generally are not trained or certified to do so, and if they do any testing, they will not report or certify the results. By contrast, Premier Veneers documents its moisture testing in great detail, so much so that the results will not only reliably tell you exactly how much moisture is in your concrete, but stand up in court in a suit against a builder, if need be.