How Humidity and Temperature Affect Your Products Once They Leave Your Shop

Posted by Rumin Mann
September 28th, 2011

In order for your customers to enjoy many years of function from their purchase of your wood product, there are some things both of you can do to maintain the look and durability of the natural wood. Wood is a natural product that is hygroscopic – it responds to changes in surrounding humidity and as a result, will lose or gain molecular moisture (water) as relative humidity (RH) fluctuates. This will cause the wood to shrink as RH drops, and swell as RH increases.

Under normal use conditions, all wood products used for millwork in kitchens and furniture are never completely moisture free. Woodwork products are manufactured from wood that has been kiln-dried to an average moisture content of 7% to 8% and maintained at that moisture content until the time of delivery to a woodworking shop. Even finished products that have been kiln-dried and coated with a protective finish will gain or lose moisture depending on the environment it is placed in.

The movement of moisture to and from wood from the surrounding environment continues to take place as the RH changes, whether this is due to seasonal changes in climate and/or building related conditions.

To avoid product failure or quality issues, it is recommended that in low humidity regions such as Alberta, an interior RH of between 30% and 45% be maintained. Other regions of Canada may require different RH levels.  Uncontrolled RH extremes below 25% or above 50% will likely cause problems. In new home construction where there has been recent concrete work, drywall taping, mudding and painting, excessive moisture is often released into the building. In these environments, the heating system may not be operating yet or the heat may be set at high levels (above 30 C or 86 F) to speed the drying process of the aforementioned operations. Placing your finished wood products into these harsh conditions could lead to problems that could affect the warranty of your installation.

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