Hardwood Floors February/March 2019

AT THE SITE

By Andrew Fulkerson

CONCRETE SUBSTRATES: Sweeping Is Not Always the Only Preparation Needed

Fig. 1: ICRI Guideline No. 310.2R and Concrete Surface

Profile (CSP) replica chips.

All photos courtesy of the International Concrete Repair Institute.

The International Concrete Repair Institute (ICRI) Guideline No. 310.2R-2013, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair , has been specifically written to aid contractors and specifiers to adequately choose proper methods to mechanically prepare concrete surfaces prior to coating or repair. The guideline identifies 10 different concrete surface profiles (CSP 1-10), and CSP replica chips are available for use in visually accepting or rejecting a prepared concrete substrate (Fig. 1). Most wood flooring adhesives require little to no mechanical surface preparation of a concrete substrate prior to installation; however, this is only if the concrete substrate complies with the flatness and moisture requirements set forth by the adhesive manufacturer. A general rule of thumb for proper hardwood flooring installation is that the substrate be flat, dense concrete that is level to a tolerance in plane of 3/16" (4.8 mm) in 10' (3 m) or 1/8" (3.2 mm) in a 6' (1.8 m) radius. If the concrete slab is not within these tolerances, you will need to prepare your concrete slab to obtain such tolerances.

Areas that are out of plane and not within the necessary tolerances can be repaired by utilizing a self-leveling underlayment placed over the slab. Most self-leveling underlayments will require a CSP 2 to 4, which can be achieved by mechanical preparation. Low areas within the center or edges of the slab, such as gouges or birdbaths, can be repaired with a patching or skim coating material depending on the depth of the repair needed, and these types of products may only require a CSP 1 to 2. Other than the flatness of the concrete slab, the moisture level in the concrete can also be a concern for the proper installation of hardwood flooring. Wood flooring adhesives are formulated for dry or wet areas, the difference being that a “dry area” adhesive can handle approximately 3 lb/1,000 ft 2 (1.4 kg/93 m 2 ) or 75 percent relative humidity (RH) of moisture vapor emitting from the concrete slab, and a “wet area” adhesive can accommodate higher values. Proper moisture testing, such as ASTMF1869 for measuring moisture emissions (lb/1,000 ft 2 [kg/93 m 2 ]) or ASTMF2170 for measuring the relative humidity (percent) within the concrete slab, is useful in determining which type

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