It is not enough to use perfectly dry lumber at 6-8% when producing cabinets and furniture.
Lumber always interacts with the surrounding air. A product manufactured with dry lumber at 6-8% is not staying within that perfect range, if the surrounding relative humidity is not appropriate. A glance at the EMC chart states, that the relative humidity has to be kept between 30-50% at a temperature around 70 degrees F for wood to stay within 6-8% moisture content, .
In case the relative humidity falls out of this “comfort zone”, wood starts picking up or loosing moisture. Changes in moisture content are often accompanied by shrinking, warping and cupping; followed by customer’s complaints.
Using a combo meter, which offers pin-less, pin and RH measuring technology, will cover all applications to measure moisture and humidity. Thus, moisture problems can be avoided and when they occur they can be tracked.
The first step is to make sure, the wood used in production is well seasoned and dried from surface to core. Handheld moisture meters are used to check for the correct moisture content when the lumber comes out of the dry kiln and before it is used in production. Pin and pin-less meters are available. Pin-less meters usually measure 3/4” deep and need a flat surface. They work great on flat boards up to 6/4” thick. For thorough testing of boards over 6/4” thick, or round and irregular shaped pieces, pin meters are recommended. The thicker the wood, the more important are core measurements. On the other hand, pin-less meters allow for checking large number of boards quickly.
Next, the relative humidity needs to stay within the recommended 30-50%. This includes any storage area, the place of production or workshop, the warehouse, during transportation and acclimation at the job site and last after the place is occupied. Thermo-Hygrometers, multi-mode moisture meters or better yet data loggers can keep track of the relative humidity. Data loggers work great, because they tell the history of any change. A swift breeze of moist air does not change the wood moisture. The wood moisture is affected by persistent higher or lower relative humidity, which a data logger can confirm.
Many of the places listed above are under the manufacturers control. It becomes more difficult to make sure the relative humidity does not fall out of the 30-50% range, when the product is on site. For flooring, cabinets or furniture to be installed, the building needs to be closed up and heat or HVAC in operation. Proper acclimation only takes place, when the present ambient conditions are the same as when the place is in use later on. The BL2 from Lignomat can record 16000 data sets for temperature and humidity and can be set for out of range audible alarms. If a data logger is left on site, there will be no more discussions about proper relative humidity conditions.
For further analysis of moisture content and relative humidity, Lignomat offers the Moisture Tracker. A data logger which records MC and RH. The instrument shows how relative humidity affects the moisture in wood.
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