concrete MOISTURE TESTING
A certain amount of water is needed for a concrete contractor to mix, place and finish a concrete floor slab, depending on the mix design, and a proportion of that water has to remain in the concrete for it to cure, or “hydrate". The rest of this moisture, which usually accounts for about 50% of the original “mix-water”, will eventually leave the concrete slab through evaporation, during the drying process. New concrete requires at least 28 days to cure, and usually at least 3-4 months for the excess moisture to evaporate, although the drying process can take up to one year.
If a floor covering, coating or other topping is installed on a concrete floor slab before this time, or additional moisture is introduced to the slab unintentionally, this excess moisture can be trapped below the surface and cause major problems for the flooring, including: staining and discoloration; failure of the bonding adhesive; bubbles or blisters on the surface; warping of flooring material; and de-bonding or "delamination". Trapped, excess moisture can also cause degradation of the concrete, itself, through the processes of efflorescence, carbonation, alkali-silica reactivity, and sulfate attack.
Specifically, in the case of acid-stained concrete flooring, and other types of decorative concrete, wet or damp areas of concrete may cause the color of a stain, dye or concrete overlay to lighten, by diluting it, or to darken significantly, through prolonged reactivity of the material and/or intensified curing of the concrete. Either way, the color effects on the floor are unpredictable, and these wet or damp areas will usually stand out from the rest of the floor. Sometimes, excess moisture will even prevent a stain, dye, overlay or concrete sealer from setting up, and drying, in the first place, or cause the material to "delaminate", that is, come up in sections, shortly after installation.
Whether new or existing concrete may have 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, high water tables, standing water, osmosis, substrate moisture vapor, landscape irrigation, pipes and drainage lines, gutters and downspouts, spills and routine cleaning & maintenance. Since concrete acts like a sponge, this excess moisture will often just disappear internally.
Therefore, every concrete slab should be tested for moisture before decorative concrete flooring is installed. Almost all stained and decorative concrete flooring product manufacturers specify this in their technical data sheets. This testing includes for both moisture content and moisture vapor transmission. There are a variety of methods outlined by ASTM International to determine these levels, but most contractors do not set aside the time or have the training and equipment to do so. We do. Premier Veneers tests concrete for moisture before every project. We use the Concrete Moisture Encounter from Tramex and are certified in concrete moisture testing by the International Concrete Repair Institute (ICRI). We are the only such certified contractor in the Michigan. (See our listing here.)
Testing involves, firstly, measuring the concrete surface to determine whether moisture content levels are within range. This takes about 10-15 minutes. If any anomalies manifest themselves, further testing on the interior of the concrete can then be done in those areas to measure the internal relative humidity of the slab. This takes several hours of work, over a 24-hour time frame, and will quantify the extent of any moisture problem so that an appropriate remedy can be pursued. If excess moisture does not have an identifiable cause, dehumidification equipment can help quickly dry out the concrete to acceptable levels. "Moisture barrier" primer coatings can also be installed to block this excess moisture from affecting the flooring installation. Premier Veneers uses an industrial grade dehumidifier from Dri-Eaz throughout acid-stained and decorative concrete flooring projects to expedite drying.