Water is an important ingredient of concrete. A certain amount of water is needed for a cement contractor to mix, place and finish a concrete slab, and a certain amount has to remain for the concrete to cure or “hydrate". The rest of this moisture, which usually accounts for about 50% of the original “mix-water”, will leave the concrete slab through evaporation during the drying process. New concrete requires at 28 days to cure, and at least 3-4 months for excess moisture to evaporate, but can take up to one year.
If a floor covering, coating or topping is installed before this time - or additional moisture is introduced to a slab unintentionally - moisture can be trapped below the surface and cause problems for the flooring. This includes staining; discoloration; adhesive failure; bubbles or blisters; warping; and de-bonding or delamination. Excess moisture can also cause degradation of the concrete itself through efflorescence; carbonation; alkali-silica reactivity; and sulfate attack.
In the case of decorative concrete flooring, wet or damp areas of concrete can cause the color of stains, dyes and cement overlays to lighten - through dilution - or to darken significantly - through prolonged reactivity and intensified curing. Either way, the color effects are unpredictable, and the wet or areas will usually stand out from the rest of the floor. Sometimes, excess moisture will even prevent stain, cement or sealer from setting up or drying in the first place, or cause it to "delaminate", or come up in sections, shortly after installation.
It is not always obvious or apparent that new or existing concrete may have a moisture problem. The problem may only manifest itself after a flooring system has been installed. Even though the concrete in question may have had plenty of time to cure and dry, outside sources of additional moisture are easily introduced through weather, high water tables, standing water, osmosis, substrate moisture vapor, landscape irrigation, pipes and drainage lines, gutters and downspouts, spills, and routine cleaning & maintenance.
As such, every concrete slab should be tested for moisture before decorative concrete flooring is installed - and almost all decorative concrete product manufacturers specify this in their data sheets. This includes 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. Premier Veneers does. We test 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 first involves measuring the concrete surface to determine whether moisture content levels are within range. This takes about 10-15 minutes. If any problem areas or anomalies are discovered, further testing on the interior of the concrete can then be done to measure the "relative humidity" of the slab. This takes anywhere from 24-72 hours and will quantify 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 quickly dry concrete to acceptable levels. Sometimes, moisture barrier primer coatings can also be installed to block moisture from affecting flooring. We use a high grade, industrial dehumidifier from Dri-Eaz throughout acid-stained and decorative concrete flooring projects to expedite drying.