Controlling the moisture content of reclaimed wood is critical both before and after installation. Antique Wood is hygroscopic, meaning it changes dimensionally with the absorption or release of moisture. Swelling and shrinking varies with the Reclaimed wood species, cut, and type of reclaimed flooring. Because engineered products' cross-ply construction adds dimensional stability, moisture control for engineered-wood flooring is less critical than for solid-wood flooring
Manufacturers kiln-dry antique lumber so it will behave predictably. During transit, delivery, and storage, it must be protected from moisture. Before installation, reclaimed wood flooring must stabilize at (acclimatize to) the temperature and relative humidity of space in which it will be installed. After installation, and even after finishing, fluctuations in environmental conditions cause shrinking and swelling.
Spaces below Reclaimed wood flooring must be dry and well ventilated. Cross-ventilate crawl spaces, and cover the ground with a polyethylene vapor retarder. If solid reclaimed wood flooring is installed over wood sleepers on a concrete slab, NOFMA recommends covering the sleepers with a polyethylene vapor retarder and making provisions for ventilating the airspaces between sleepers.
For a comprehensive discussion of the effects of moisture on wood, refer to NWFA A100, Water and Wood: How Moisture Affects Wood Flooring, which is available, free of charge, on the NWFA Web site listed in the "References" Article in these Evaluations.
Before installing reclaimed wood flooring over a concrete slab, NWFA recommends a maximum moisture-vapor-emission rate of 3 lb of water/1000 sq. ft. (1.36 kg of water/92.9 sq. m) in 24 hours when slabs are tested with a prepackaged calcium chloride test. This emission rate corresponds with recommendations made by other floor covering industries to avoid adhesive failures of adhered systems. However, MFMA recommends a maximum moisture-vapor-emission rate of 4.5 lb of water/1000 sq. ft. (2.04 kg of water/92.9 sq. m) in 24 hours. To be safe, consider specifying the more conservative rate. To ensure consistency among test kits and testing methods, the Section Text references ASTM F 1869, Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.
Temperature, relative humidity, and ventilation affect concrete drying time. To dry adequately, a slab allowed to dry from only 1 side generally takes 30 days for every 1 inch (25 mm) of thickness.
Concrete-slab substrates must be dry and protected from subsurface moisture by appropriate grading and drainage, a capillary water barrier of porous drainage fill, and a membrane vapor retarder.
Reclaimed Wood flooring installations must accommodate movement. An expansion space is required at the perimeter of the installation. For larger installations, more expansion provisions may be required.
MOISTURE Content and Reclaimed Wood