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The most challenging and difficult of resilient installations is the below-grade installation in basements.  The term below grade means a slab that has been cut into a hillside or below the grade of the soil.  When a basement or below grade installation is encountered it is necessary to pay strict attention to the slab for moisture conditions.

Vapor retarders (Photo 1): The first thing is to determine if a vapor retarder has been used.  In residential installations vapor retarders either were not used or a poor grade of retarder was.  Even though a plastic was used does not mean the vapor retarder is a good value.  Many times a contractor will use a cheap plastic that is either too thin and will be easily punctured or is a plastic that is affected by ultraviolet light (sunlight) and will decay after the concrete is placed.

A slab that is below grade is very susceptible to hydrostatic pressure.  Hydrostatic pressure, a term used loosely, only occurs below-grade and is the reason why so much caution must be used when installing in basements.

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Visual examination: When you walk into a basement the first thing to do is to do a visual exam of the slab.  Look for things like; damp spots under boxes and or buckets, dampness along any cracks in the concrete or alkali deposits along cracks and joints that will present a possible red flag regarding the possibility of moisture problems. Photo 2 shows an example of damp spots. Photo 3 shows an example of alkali deposits.

Installers should plan to remove painted surfaces to prevent any bonding issues.  If the surface is painted, look at the condition of the paint to see how well it is bonded to the concrete.  This could be another sign of moisture in the concrete slab.Finally, check the slab for porosity.   The lack of porosity can be a sign of sealers or curing compounds.  If on the slab, these should be removed as well.

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Moisture testing (Photo 4): Moisture testing, unfortunately, is not done in most residential installations.  Moisture testing should be done.  It is the best way to safeguard against moisture related failures.  The use of the RH (in-situ) probe following the ASTM F-2170 protocol is the most accurate method of determining the moisture content of a slab.  Each resilient manufacturer has there recommendation for the relative humidity requirements for their materials.  Plus the RH probe test is faster and easier to do than the old calcium chloride tests, with a smaller margin of error.

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Moisture Treatments: If it is determined that a moisture condition exists, it will be necessary to treat the concrete with a moisture mitigation treatment. There are basically two types of treatments:

Penetrants (Photo 5) are sprayed-on or in some instances rolled-on.  They are designed to penetrate into the surface and create a barrier that slows the migration of moisture out of the slab.  When using penetrants, the amount of penetrant applied is critical; too little does not suffice and too much can result in a bonding issue.

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Coatings (Photo 6) are applied either with a roller or squeegee.  Coatings are the more expensive of the moisture treatments and in my estimation the better of the moisture treatments.  Coating to be effective must be applied in a specified thickness and often two coats.

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Moisture treatments are very important and rely upon a lot of attention to detail. (Photo 7)  Failure to comply with installation requirements will result in an installation failure that can be very expensive.