Hardwood Floors August/September 2017

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Thus, wood flooring is always undergoing at least slight changes in moisture content. These changes are usually gradual, and short-term fluctuations tend only to influence the surface of both solid and engineered wood flooring. Longer-term fluctuations can have greater effects on flooring, and in some cases, can cause irreversible damage. These changes can be slowed, but not entirely prevented, by protective coatings. Maintaining consistent temperature and humidity levels year-round will minimize moisture and dimensional changes. In actual practice, shrinkage and swelling may be diminished by the boards’ proximity to each other, installation methods, fastening systems, and moisture interactions from the substrate. All of these factors can influence how an installed floorboard performs when it changes MC. The physical effects these changes can have on wood and wood flooring products can vary from one floor to the next, based on a few different variables. Grain Angle/The Cut: Wood is an anisotropic material, meaning it shrinks and swells differently in each direction within the wood. Different woods exhibit different moisture stability factors, but they always shrink and swell the most in the direction of the annual growth rings, tangentially, about half as much across the rings, radially, and only in minuscule amounts along the grain, longitudinally. This means that solid plainsawn flooring will tend to shrink and swell more in width that solid quartersawn flooring, and that most solid flooring will not shrink or swell measurably in length. Keep in mind, no two trees from the same species are identical, no two boards from the same tree are identical, and properties can vary even within one individual plank of wood. Engineered Wood: Engineered wood flooring exhibits different reactions to these changes in moisture. Each layer (lamina) of engineered flooring runs perpendicular to adjoining layers, which creates a more dimensionally stable product. When exposed to longer-term fluctuations in relative humidity and temperature, each layer begins to react. As one layer reacts in one direction, the adjoining layers react with similar forces in the opposite direction. This can result in shrinking and swelling not only along the width of the boards but along the length of the boards as well. Moisture Testing: Moisture content from 5-30 percent may be determined using various moisture meters developed for this purpose. Both types of meters will give generally reliable readings somewhere between 5-30 percent MC. The most accurate method (however not practical on an installed wood floor) to determine moisture content is to follow the laboratory procedure for the oven bake method

(following ASTMD4442) by weighing the piece of flooring with moisture, removing the moisture by fully drying it in an oven (102 °C - 105 °C or 215 °F - 220 °F) and then reweighing.

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49 the magazine of the national wood flooring association