Cedar trees not only have a pleasant aromatic scent; they are incredibly strong and popular as a building material. One species of cedar found in the United States, the Western Red Cedar, thrives in wet environments. Cedar is moisture resistant, preventing rot and decay, which makes it perfect for outdoor projects, such as wood decks, porches, or gazebos.
The length of time it takes for cedarwood to dry is based on whether you’re air-drying or kiln-drying the wood and whether you’re drying logs or lumber. Air-drying cedar wood takes anywhere from three to twelve months. Kiln or heat drying significantly speeds up the drying process and, depending on the moisture content, it can be as little as 10 hours.
Air-drying times can be affected by the rate the water moves through the wood, the relative humidity in the surrounding air, and the temperature. In this article, I will strive to give you an understanding of cedarwood, how water and drying time are connected, when to use green or dried cedar and the drying methods.
The Moisture Content of Cedar
Softwood, such as cedar, can be dried faster than hardwoods as it can be subjected to higher temperatures without damage and is less dense, meaning the water is released at a faster rate.
Western Red Cedar typically has a moisture content of around 25 percent when green (source). The common practice is to kiln dry Western Red Cedar to 12 to 15 percent moisture content for construction purposes or 6 to 8 percent for furniture and cabinets (source).
Hardwoods, such as oak, can take longer to dry than softwood due to the higher concentration of water and tree density. Oak, when green, has a typical moisture content of 60 to 80 percent (source).
There are two types of water found in trees: free water and bound water. Free water travels through cell lumens and all open spaces in the tree. In contrast, bound water penetrates the cell walls and binds to the wall through the chemical process of hydrogen bonding (source).
Softwoods contain mostly free flow water found in the outer sapwood, allowing for much faster than hardwoods. It takes longer to completely dry the inside of the wood compared to the outside because the outside is the first part of the tree exposed to the heat (source).
Greenwood is high in moisture content, making it soft and flexible. It is excellent to use on a lathe so long as you take into account the likelihood of it warping or cracking as it air dries (source). However, when the wood is green (freshly cut), it should not be used for building.
Even at a moisture content of 25 percent, there is a high probability of the greenwood warping or cracking as it dries, which will negatively affect whatever you choose to build, whether it’s furniture or a deck.
There are various species of cedarwood available. Western Red Cedar, Inland Red Cedar, Eastern Red Cedar, Yellow Cedar, Port Orford Cedar, and Tennessee Red Cedar are commons examples.
No matter the species you choose, it could take anywhere from 6 months to 1 year to air-dry a log that is 18 inches in diameter. A freshly cut 2×6 cedar board may dry in as little as 90 days.
Air-drying is a much slower process than kiln drying wood, but it is cheaper, especially for the home woodworker.
Kiln-dried wood is best for construction. It produces a consistently stable and robust product for building and will have little to no warpage. However, if smaller projects are what you enjoy working on, air-drying is best because air-dried wood is not as hard on woodworking tools as kiln-dried.
Cedar, being a softwood, will kiln-dry faster than a hardwood such as oak. Cedar will dry in about four to ten days, whereas oak can take up to 25 days (source).
Types of Wood Drying Kilns
Overall, kilns operate under the same premise. The kiln is a room or chamber used to balance and control the humidity, temperature, and airflow to dry the moisture out of the wood and bring it to acceptable moisture content.
Other types of kilns include electric, hot water, hot oil, solar, and hot air directly fired at the wood. The hot air kilns are generally only used for drying softwood because it is difficult to control humidity (source).
Most drying kilns in the United States are steam heated. If drying hardwood, the temperatures do not generally go above 190 degrees. When drying softwoods, such as cedar, temperatures need to reach upward of 240 degrees as cedar dries quickly. The higher temperature fans and baffles control the movement of air (source).
All lumber is kiln-dried using a controlled schedule. Without a controlled drying schedule, the chances of defects are high. Possible examples include discoloration, warping, cracking, splitting, and even small surface openings (source).
Another defect of uncontrolled drying is case-hardening. The case-hardening defect occurs when the outer shell of the log or lumber dries faster than the inner core. As the shell attempts to shrink, the core’s moisture is too high, resulting in the shell drying stretched out.
Later, as the core begins to shrink, this process is reversed, the stretched shell keeps the core from totally shrinking. In extreme cases, the core splits or collapses, which is called honeycombing.
Provided the above factors have been carefully controlled, using a kiln will dry wood evenly and quickly. Drying the wood evenly from the outside shell to the inner core is important. If not dried evenly, the wood will warp or crack, such as when applying an accelerated air-drying process.
The amount of time it takes is dependent on kiln performance and the rate of air circulation (source).
While times are difficult to nail down precisely, a 1-inch board of Eastern Red Cedar can take 6 to 8 days to go from green to 6 percent moisture content. A Western Red Cedar board of the same thickness would take 10 to 15 days to reach 6 percent moisture content (source).
Stacking and Sealing Lumber
Whether air-drying or kiln-drying, you want to make sure your lumber is properly stacked and sealed.
The method you use to stack your wood is essential for it to dry evenly. When stacking your wood, you will want to use the stack-and-sticker method, which is especially efficient when all your lumber is the same size and thickness.
Stickers are small pieces of wood used to separate the planks while drying. Generally, place stickers about every 12 inches or if the planks are thick every 16 to 24 inches.
As soon as you have stacked your lumber, you will need to add weight to the top of the stack. The bottom planks have a good amount of weight on them, but the top will not. Weighing down the top of the stack will prevent warping and distortion. You want your lumber flat and stable (source).
You do not want the ends to shrink faster than the rest of the wood, as that would cause an enormous amount of stress and problems later when working with it.
Seal both ends of the logs or lumber to keep the wood from drying out too quickly, which will cause splits and end-grain checking.
The key is to make sure the ends are thickly coated as soon as possible (source). Moisture escapes from the wood’s ends 10 to 12 times faster than the rest of the wood, so sealing the ends helps the wood dry uniformly and prevents decay.
The main reason a wood board will warp (or distort) is uneven shrinking while drying. However, there may also be a pre-existing flaw in the wood, which results in bowing, crooking, and twisting of the lumber.
In addition to proper stacking techniques, methods to prevent warping include avoiding very young wood as it is unstable and not processing branches or leaning trees, which is where you find reaction wood.
On a cedar tree, reaction wood is found on the underside of the branch or trunk and is called compression wood. Lumber made from the compression wood of a cedar tree is of lower quality (source).
Knots also cause problems with uneven shrinking. They may loosen during drying and create abnormalities in the grain (source).
Depending on your project, whether carving or building, using dried lumber is a best practice, especially kiln-dried, as it makes the wood stronger.
Cedar is an excellent choice for outdoor projects as it is moisture resistant and will resist rot and decay. Whether air or kiln-dried, cedar is the perfect choice for all your outdoor projects.