Kiln-Dry: What That Means for Wood

Forestry, done well, is a combination of science and nature which results in strong, durable wood. However, all wood species are harvested in the “green” condition, which is a term for the properties which behold wood in the wild.

There’s Green Wood

Freshly Cut TreeMany observers would be shocked at the high (“green”) moisture content (MC) of some wood species. Since trees comprise an autonomous eco-system of water and nutrients, it stands to reason that sapwood (the layer next to the bark) is generally higher in MC than heartwood (inner wood which has died). Sapwood distributes water and nutrition through a tree. The heartwood, or inner wood, becomes infiltrated with gums, resins, and other materials.

This makes it more resistant to moisture flow and thus, the heartwood usually requires longer drying times than sapwood. Sapwood and heartwood will affect the drying curves for each wood species.

A wood’s MC is also a dynamic exchange between the wood itself and the surrounding air. When the relative humidity (RH) in the air rises, wood absorbs moisture from the air; when the RH falls, wood releases moisture into the air. This occurs naturally, and it occurs throughout a wood product’s lifespan even after it has been harvested and kiln-dried for human use. Wood producers, builders, and consumers need not fret over such an organic, natural process, but a thorough knowledge of it will guarantee success with wood in all sorts of product applications.

The key to wood strength and performance over time is to dry the wood appropriately to its optimum MC depending upon the end product’s service conditions and the end product’s installation destination.

There’s Kiln-Dried Wood

Kiln Dried Wood

Wood in “green” condition must be kiln-dried in order to be used as construction grade lumber for building purposes, as an example. Lumber production is a complex process in which green timber is sawn, dried and processed. The natural air-drying of lumber can be a long process, so oftentimes lumber will be kiln-dried to speed the process along. Kiln-drying is basically a process of placing sawn lumber into kilns where heated air is circulated and the temperature and RH of the kiln is controlled for the purpose of reaching the wood’s equilibrium moisture content (EMC): a balance between the MC of the wood, and the RH of its surrounding environment, depending upon the end wood products application specifications. Once the EMC is achieved, a wood’s MC can vary with slight changes in the RH of the surrounding environment without jeopardizing the strength and structural integrity of the end wood product.

Lumber producers deploy expansive and expensive wood MC control systems at all phases of wood production. Kilns are an integral part of the wood’s MC measurement and management process, as the kiln-drying procedure is where the green lumber is dried to its optimum EMC.

There’s a Moisture Meter to Measure It

A wood moisture meter is crucial in establishing and maintaining healthy wood MC levels at each stage of lumber production. A wood moisture meter is a tool which measures the wood’s MC. As green wood circulates for processing in a mill, in-kiln and in-line MC systems measure and document the wood’s MC and track the efficiency of the kiln-drying process. Professionals carefully monitor and control the process to optimize the harvest. Kiln operators and quality control personnel deploy hand-held wood moisture meter products to conduct as many spot-checks as needed to verify the mill’s kiln-drying efficiency.

Ecology is merging with forestry in the modern era to make MC measurement and control an ongoing matter of wood maintenance. Wagner Meters, a family-run industry leader in MC measurement technology, has developed several wood moisture meter products to assist industry specialists, retailers, wood flooring installers and owners and hobbyists in protecting their investments.

As the world awakens to its own nature, wood moisture meter technology has advanced greatly. Wagner Meters features pocket size digital and analog styles of its wood moisture meter products. Now there’s a cost-effective, reliable wood moisture meter to suit any wood measurement application goal, from the home to the lumber producing mills.

To learn more, call: 800-634-9961.

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Larry Loffer

Larry Loffer is a senior technician at Wagner Meters, where he has over 30 years of experience in wood moisture measurement. With a degree in Computer Systems, Larry is involved in both hardware and software development of wood moisture measurement solutions.

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