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  • Kiln Drying Douglas Fir: An Essential Process

    Posted on April 5, 2011 by nell

    One of the greatest concerns in using Douglas fir for construction (and especially flooring) is the moisture content of the lumber. Wood can absorb and secrete moisture depending on its environment. For Douglas fir used in wood flooring, controlling the shrinking and expanding of planks is essential, which is why flooring should always be acclimatized before it is installed. If the planks swell too much, they can push up against each other or the walls, causing damage to the wood and moulding; if the planks shrivel up, the space between boards expands to the point of creating hazardous gaps in the floor.

    Each variety of lumber has a point of moisture equilibrium – the moisture level at which the wood is most stable (when the vapor pressure within the wood is equal to that of the ambient space above). When left to its own devices Douglas fir, or any lumber, will absorb or evaporate moisture until it reaches its equilibrium. To ensure the durability of the wood, planks should be at equilibrium before being installed.

    This can be problematic, however, when you consider that trees – especially Douglas-firs grown in the lush Pacific Northwest – have incredibly high moisture content at the point of being cut down. Something has to be done to the lumber before it is sold to ensure moisture equilibrium in the final product. Drying is an important step in the process of acclimating wood to a new environment (specifically, drier interior spaces). Drying reduces the moisture in lumber to replicate the future conditions to which the lumber will be exposed. This process can take place out in the open; this is known as air drying.

    There is also a faster, more precise alternative: kiln drying. Kilns for wood drying are typically large spaces with heated coils on the ceiling. Nearby fans redirect the flow of warm air evenly around the room. The heat greatly speeds up the drying process, and the stable environment allows for wind control (an important factor in effectively drying wood). Kiln drying can also be carried out in stages through environmental control, which is ideal for drying the wood at an optimal pace.

    There are other factors to consider in terms of kiln drying. One added benefit of the process is, for salvaged products, that the heat kills insects and their eggs. One drawback is the increased price of a product that has been kiln-dried. However, the benefit of kiln-dried wood is typically great enough to warrant the extra charge. The long-lasting effects of kiln drying – and the money you could save on avoiding frequent refurbishing or replacement of your Douglas fir floors – certainly make the process and the cost worth it in the long run. All of AltruFir’s Douglas fir products are kiln dried to ensure that a more stable product is made available to the consumer.

    - Ian Friedman

    This post was posted in All Entries, Douglas Fir Flooring, Douglas Fir Trim, Care & Maintenance and was tagged with Douglas fir flooring, douglas fir floors, kiln dried lumber, kiln dried flooring, kiln drying

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