When Kiln Drying Doesn’t Work
Written by Wagner Meters, published first by Floor Trends (November 2014 issue)
Most unfinished wood you’ll find at a lumberyard or flooring supplier has been kiln-dried to bring its moisture content (MC) into a workable range and help prevent problems over the life of the finished product.
Kiln drying is a controlled process that speeds the natural drying of “green” lumber into a wood product that’s much less prone to warping, buckling, splitting, and other moisture-related defects.
However, it’s important to understand that kiln drying doesn’t guarantee a piece of wood flooring will never have moisture-related problems. Kiln drying is only one step in wood’s journey from a living tree to a finished product.
What Does Kiln Drying Wood Really Do?
A living tree is a network of interconnected cells and pathways that carry water from the ground up through its trunk and branches to the tips of its leaves. When the tree is freshly cut, that moisture is still in the wood.
The moisture will eventually evaporate, but this process (called air drying, because the moisture is carried away by the surrounding air) is slow. And if lumber dries too quickly, it can split, warp, or crack, damaging otherwise useful wood.
Kiln drying uses a combination of heat and airflow to lower the MC of green lumber faster than air drying can. The target MC varies by wood species and end use, but the goal is for the wood to come out roughly in balance with the conditions where it will be used.
That’s why each charge (or kiln load) is sorted by species and dimensions: to make the process efficient, to get even final MC levels across the charge, and to reach the target MC for the product.
In-line and in-kiln moisture measurement systems help determine when the wood has reached its target MC.
Mills and manufacturers invest time, money, and training in their drying processes to deliver uniform wood products at the correct moisture levels for their customers. A well-run kiln removes excess moisture efficiently while minimizing the damage that drying too quickly can cause.
So if the wood leaves the kiln at the required MC, the job is done, right?
Unfortunately, no.
What Kiln Drying Doesn’t Do
Wood is hygroscopic, which means it constantly interacts with the moisture around it. Even after the tree is cut and the lumber is dried, the wood’s cells will still absorb or release moisture to reach balance with their environment.
If the surrounding air’s relative humidity is higher, the wood absorbs some moisture. If it’s lower, the wood releases moisture. This continues until the wood reaches a point of balance with the surrounding air, called its equilibrium moisture content (EMC).
Why does that matter?
Kiln drying removes most of the wood’s moisture, but the wood doesn’t lose its ability to take moisture back in. Whether it comes from direct contact with water, moisture in an adjacent material, or humidity in the air, wood will absorb moisture it’s exposed to. Kiln drying doesn’t lock in a wood product’s MC; it just brings the moisture down to a workable range.
Wood’s MC will always be a variable, not a constant.
That’s why kiln drying is only the first step. At any stage after the kiln (shipping, manufacturing, storage, or installation), wood, including manufactured wood flooring, can lose more moisture in a dry environment or absorb moisture in a humid one, changing its MC and possibly its dimensions. That can create real problems for you as the end user, especially if you assume kiln drying alone protects against moisture-related problems.
Moisture Measurement in Wood Flooring
Wood flooring installers know wood’s MC changes with its environment. It’s just as important to let each bundle acclimate to the job site before installation as it is for the manufacturer to monitor MC accurately before the flooring leaves the plant. Any flooring must have time to adjust to the job site before installation, sanding, or staining begins.
Whatever your application, the wood you use needs time to adjust to the environment where it will be worked or installed.
How to Accurately Monitor Wood’s MC
A simple, easy-to-use wood moisture meter gives you quick, accurate, reliable readings to help make sure an installed floor won’t develop moisture-related problems. Pinless wood moisture meters, like our Orion® meters, can be used as often as needed without marking the floorboards or leaving holes that will show once the finish is applied.
At Wagner Meters, we know an accurate wood moisture meter keeps you informed at every step of your process. Our wood moisture meters are designed to help wood flooring installers make sure their wood is ready for the project at hand.
From the kiln to the start of every wood flooring project, the first order of business is to measure and make sure the wood has acclimated to the right MC before work begins. Kiln drying is only the first link in the chain of MC management needed for durable, beautiful finished wood projects.
Free Download – How to Choose the Right Industrial Hand-held Moisture Meter for Your Mill
Tony Morgan is a senior technician for Wagner Meters, where he serves on a team for product testing, development, and also customer service and training for moisture measurement products. Along with 19 years field experience for a number of electronics companies, Tony holds a B.A. in Management and his AAS in Electronics Technology.
Last updated on October 13th, 2026
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We are putting down Kentwood Acaia wood. It been in our home for 2 months. Humidity level 11.4. The installer comes by every 10 days. The last week we have been running 2 dehumidifier to help. Today he stopped by it’s still at 9:4. We can’t seem to get it lower. We turned off the humidifier in the house. Live in Chicago. Getting frustrated. What should we do?
I have an issue with large dimension wood 9’ x 8” coming out of a kiln dried that has large cracks and is warped. How can this be solved
Cracking can be caused by different things such as too much heat applied too fast, airflow issues in the kiln, drying temperatures too high. Warping can be caused by drying too slow, or not using top weights.
Kiln drying wood has so many factors that need to be taken into account; wood species, heat type, temperatures, dimension, kiln size, kiln type, seasonal weather changes, even the time of year when the lumber was cut, are but a few of these factors. There are just too many variables to be able to answer your question effectively.
I suggest going to the Forest Products Laboratory at: Forest Products Laboratory-Kiln Drying articles, and researching the kiln drying literature they list for more comprehensive information on kiln drying problems and solutions.
Another possibility is taking a lumber drying workshop or kiln drying course. These are offered as classes, or on-line, and also give you the opportunity to work with other kiln operators to get real world answers to your questions. Oregon State University is one of the many organizations that offer lumber drying workshops: OSU-Lumber Drying Online Workshop.
Would you use a moisture meter for wood that has been dead in log form for many years then sat out drying in 99+ degree weather after being milled for several months? Or is it just necessary when dealing with kiln-dried wood?
Just because the tree is dead, and has been milled, is no reason to assume it is dry. It may be, but making that assumption could ruin whatever project the wood is slated for. This is especially true for hardwood, exotic woods and even kiln dried wood. The best way to ensure the wood is dry and ready for a project is to test it using a quality moisture meter. The Wagner MMC line of moisture meters is a great choice for this type of application. Please check and see which meter would best suit your needs:
https://www.wagnermeters.com/moisture-meters/comparison-matrix/