Preparing Concrete for Resilient Floor Installations

Identifying issues and following recognized standards helps assure best results
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Sponsored by Interface
By Peter J. Arsenault, FAIA, NCARB, LEED AP
This test is no longer available for credit

Other general guidelines relate to things like the surface of concrete floors being dry, clean, smooth, and structurally sound in order to be acceptable for resilient flooring. They also include proper filling and patching of any surface irregularities (cracks, grooves, depressions, etc.) with a latex patching or underlayment compound as recommended by the resilient flooring manufacturer. In general, the goal is to have a floor that is smooth and flat within 3/16 of an inch across 10 feet. Note that expansion joints, isolation joints, or other “moving” joints that are part of the structurally designed floor slab should never be filled, covered with resilient flooring, or otherwise restricted. Rather, they should be covered with an expansion-joint covering system. The final general guideline has to do with acclimation of the flooring products, meaning they should be delivered and stored in the space where they will be installed for at least 48 hours before the actual installation occurs. Temperature and humidity guidelines are provided with the intent that those conditions continue during and after the installation as well.

  • Testing procedures for moisture and PH levels: The standard recognizes that no matter how good the specifications and workmanship might be, the only way to be sure about the conditions of the floor slab is to test them. Therefore, it provides detailed information in the standard and appendices on how to test for acceptable pH levels in the concrete to be sure they are compatible with the resilient flooring materials. For testing of moisture levels, it references other ASTM standards, including ASTM F2170-18 (discussed more in subsequent paragraphs below). In all cases, they defer to manufacturers guidelines for their own products and indicate that in the case of any conflict, the most stringent requirements shall apply.
  • Guidelines for preparing new concrete floors: The primary focus of the guidelines for newly constructed floors is to be sure that the concrete is completely dried, not just cured. The standard provides some general and detailed information on this topic, indicating that differing conditions will produce differing drying times before moisture testing should be considered in advance of the installation of resilient flooring.
  • Guidelines for existing concrete floors: When approaching a project with an existing slab and finishes, there has to be careful analysis of the proposed substrate. Existing adhesives, underlayment, and flooring may pose a health risk during the removal process. Mechanical removal is preferred by most resilient flooring manufacturers since chemical residue may “adversely affect” adhesives, primers, underlayments, and new flooring. Once the existing finishes and adhesives have been removed, the inspection of the concrete should entail the same process as one would follow for new concrete floors.
  • Remedial measures: In the event that the conditions found are not suitable, some type of remedial measure is needed to correct the situation. This does not mean breaking up and removing the concrete floor and starting over; rather, ASTM F710 suggests that an additive material can be placed on top of the slab. This can take the form of an acceptable patching material, a continuous underlayment layer, or a topical finish. These options can help correct deficiencies in the surface or even add a layer of moisture protection between the slab and the flooring.

ASTM F710-17 includes three appendixes that, while designated “non-mandatory,” contain valuable information all geared toward additional understanding and inspection of concrete floor slabs for the installation of resilient flooring.

Testing for Concrete Floor Moisture Levels

With the multiple references to the problems and significance of moisture as a critical concern for resilient flooring, manufacturers of such flooring often require actual moisture testing be performed on a concrete floor slab before the flooring is installed. The recognized procedure for conducting that testing is ASTM F2170: Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes. Its designated scope is to provide a test method that “covers the quantitative determination of percent relative humidity in concrete slabs for field or laboratory tests.” In this case, the standard defines relative humidity as the “ratio of the amount of water vapor actually in the air compared to the amount of water vapor required for saturation at that particular temperature and pressure, expressed as a percentage.”

  • Summary of test methods: The basis of the testing in all conditions is the use of a small relative-humidity probe that is inserted into a hole in the concrete slab. Such holes are generally ¾ inch in diameter or less and 20–40 percent of the depth of the concrete slab measured from the top (actual size recommended depth vary based on construction conditions). The holes can be drilled using a rotary hammerdrill in hardened concrete or formed using a hollow cylindrical tube placed during forming in fresh concrete. Either way, the resulting hole is intended to receive a plastic or metal liner open only at the bottom and top, into which a humidity probe and digital meter are placed according to the specific parameters listed in ASTM F2170.

The standard indicates that three tests shall be performed for the first 1,000 square feet of floor and at least one additional test for each additional 1,000 square feet of floor. Locations should take into account potential high-moisture areas, and at least one should be within 3 feet of an exterior wall. Once the concrete is deemed ready and all probes are properly in place, the relative-humidity readings are taken and recorded, all according to the instruction in F2170. When complete, the hole liners and probes are removed and the small remaining holes filled with patching compound rated for the depth of the patch.

  • Reporting: The final step of the testing is to provide a written report of the findings. This will be important not only for deciding whether to proceed with floor covering but also if other problems arise that are not related to moisture as documentation of the acceptability of relative moisture conditions. F2170 lists eight items that are needed at a minimum in the report, including project name and location, testing dates/times, and people involved. It then seeks the specifics of the tests, including location and depths of each probe, the measured relative humidity in each, the temperature in each, the ambient air temperature, and the details of the probe itself. Finally, it requires that any observations that would impact the interpretation of the results to be disclosed and discussed.

The full details of this testing along with stated limitations and cautions are all described in the F2170 document and should be referred to for a complete understanding.


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Originally published in Architectural Record
Originally published in October 2019