Wood drying or seasoning lumber or timber seasoning in the UK refers to reducing the moisture content of wood prior to its use. The two most important issues are 1) the level of moisture desirable and 2) the means to achieve this.
With regard to the level of moisture, for some purposes wood is not dried at all, prior to its use. It is used as is, "green". For other purposes wood must be in equilibrium with the outside air, as in much construction wood. For use indoors, as in furniture, wood must be in equilibrium with the air indoors.
With regard to the means used in drying a distinction is made between air-dried wood (AD) and kiln-dried wood (KD). There are many different types of kilns, as time used for drying is an economic factor, and new types of kiln are constantly being developed to reduce drying time.
Usually wood is sawn prior to drying, but this is not always so. As drying in the log takes a long time, especially for big logs, sawing prior to drying is the rule. If wood is to be kiln dried it will always be sawn first.
Kiln drying vs. Air drying
Kiln drying is a very ambiguous term used in the log home industry as well as in the dimensional lumber industry. Kiln dried means “Surface Dried”. In the log home industry kiln dried standards are only 1 inch in to the log at 19% moisture content or less. Moisture is not regulated past the 1 inch mark. This limitation is due to the moisture meter used where the pins can only penetrate into the log 1 inch. So when any manufacturer states that their logs comply to the standards for the industry you now know that their logs are dried to 1 inch and they do not know what the bound cell water is past that point, your logs will shrink excessively and you will have to chink your home at $6,000 per 1,000 square foot of home every 5-6 years as the bound cell water comes out.
I can count on one have the log home manufacturers that can kiln dry to the core and can prove it. These manufacturers us a cut in the top of the logs allowing the hot kiln air to go to the center of the logs and dry from the inside out as well as the out side in taking out the bound cell water so the logs will not shrink like other manufacturers.
Manufacturers that air dry their logs will tell you that kiln drying cost too much money so they let their logs sit out and dry naturally. Some manufacturers that kiln dry use a wood stove to burn up bi-products from their mill and utilize solar panels to heat their kilns making kiln drying very affordable and cost effective for the consumer who will not have to chink their home.
Air drying is just what it is saying. Manufacturers let their logs lay out and naturally dry down to the industry standard of 19% at 1 inch. What puzzles me is if a manufacturer has the logs sitting out air drying in a geographic location that the year round relative humidity is over 80% and they claim they dry to 19%... the math doesn’t come out right. You can easily see what I am saying.
Manufacturers give you an average moisture content and this sounds good to any uneducated consumer, but do you really know what they are saying? No. A manufacturer takes a log that has died in the forest. Now when the tree dies gravity pulls the moisture down towards the stump. When the tree is laid down one end that was on the stump could be 50% moisture and the top could be 30% and all variations in-between. The manufacturer weighs the log and put in the kilns to dry to only 1 inch in at 19% moisture to comply to industry standards. They pull the logs out, weigh them again, use a mathematical formula and derive at an average moisture content. Well the truth is they do not know actually how much bound cell water is at the core of the logs and one end will shrink more than the other end. You have an average from one end to the other. You need to find a manufacturer that can give you a constant moisture content and put in writing that you will never have to chink your home. You will see many manufacturers not wanting to do business with you. Only manufacturers using a drying Kerf can give you a constant moisture content because they have access to the core to test core moisture and the others do not. Give any manufacturer this example and see how they answer. Say you have a log 10’0” in length and 10” in diameter. At 5’ and 5” in what is the moisture content. ((% can not tell you unless they pull a plug out of the log of cut it in half to be able to test with a moisture meter. Only a couple can tell you straight forward.
Again, do you home work and know what you are buying.
Published by University of Log Homes