We do not recommend solid hardwood flooring be installed directly to concrete without the addition of other subflooring materials to which the flooring can be fastened. Some adhesive manufacturers have had substantial success with direct glue down applications using a variety of different adhesives and moisture retardant systems. Follow the adhesive manufacturer's recommendations and check their warranty coverage. We will not be responsible for claims associated with direct glue applications of our solid hardwood flooring products since we neither make nor recommend an adhesive for that purpose.
Concrete Moisture Tests
All concrete subfloors should be tested, and results documented, for moisture content. Visual checks may not be reliable. Test several areas, especially near exterior walls and walls containing plumbing.
Wood/Concrete Subfloor Systems
Fastened to concrete:
Concrete must be of high compressive strength, 3000 PSI or better. Install a suitable moisture retardant followed by a plywood subfloor with a minimum thickness of 3/4" (19 mm). Allow 1/2" (13 mm) expansion space around all vertical objects and 1/8" (3 mm) between all flooring panels. In general, smaller panels [less than 4' x 8' (1.2 m x 2.4 m)] oriented at 45 degrees (preferred) offer better results. The panel must be properly attached to the subfloor using a minimum of one fastener per square foot and more if necessary. Use pneumatic or powder actuated fasteners. Do not hand nail the subfloor with concrete nails. Install a moisture retardant barrier with joints lapped 6" (15 cm) and begin installation of flooring using 1 1/2" (4 cm) fasteners.
Floating subfloor :
Install a suitable moisture retardant followed by a plywood subfloor with a minimum thickness of 3/8" (9.5 mm) [1/2" (13 mm) preferred]. Allow 1/2" (13 mm) expansion space around all vertical objects and 1/8" (3 mm) between all flooring panels. Install a second layer of plywood, the same thickness, at a right angle to the previous panels, offsetting the joints 2' (61 cm). Staple together with staples that will not penetrate the first layer of subfloor. The staples should have a crown width of 3/8" (9.5 mm) or more. Install a moisture retardant barrier with joints lapped 6" (15 cm) and begin installation of flooring using 1-1/2" (4 cm) fasteners.
Solid wood flooring exceeding 4" (10 cm) and above in width cannot be installed directly to screeds. Screeds should be installed 9" (23 cm) apart in rivers of adhesive, at right angles to the flooring to be installed. Do not begin installation until all adhesives are properly cured. Install moisture retardant over the screeds prior to installation of the flooring.