Controlling Wood Moisture Content
If you’re a woodworker, you’ve probably invested in a number of tools including saws, planers, sanders, and various measuring devices. However, there’s one tool no woodworker should be without — a quality wood moisture meter. If you don’t already have one, it’s time to go out and make a purchase. Here’s why…
Why It’s Important to Measure and Control the Moisture Content of Wood
If you’re a woodworking professional who creates and sells high-quality wood projects you don’t want a customer ending up with a piece of furniture or cabinetry that’s going to experience joint failures or openings, warped panels, uneven tabletops, or cracked finishes. It would hurt your reputation and your pocketbook. Unfortunately, that could happen if you don’t know how to measure and control the moisture content of wood. In fact…
According to leading woodworking and wood manufacturing experts like R. Bruce Hoadley, 80-90% of woodworking and wood products manufacturing defects are related to excess moisture.
This happens because wood is hygroscopic. In other words, wood is continually interacting with the environment. If there’s more moisture in the air than there is in the wood, the wood will absorb moisture until the wood and the air have the same moisture level. The same thing happens when there’s more moisture in the wood than the air. In this case, the wood will release moisture back into the air until the two are in balance.
When the wood is no longer releasing or absorbing moisture, we say that it has reached its Equilibrium Moisture Content (EMC). To put it another way, wood is always trying to reach its EMC.
Before starting any wood project such as building a cabinet or laying down wood flooring (including wood subfloors) the wood must be allowed to reach its EMC. Here’s why.
Wood changes size as its moisture content goes up and down. When wood’s moisture content increases, it expands. When it’s moisture content decreases, it shrinks.
If the wood hasn’t reached its EMC prior to being used in a project, it will continue to either expand or shrink after the project is complete. If this happens, moisture-related deformities could result.
So, prior to being used in any project, wood needs to reach its EMC in the environment where the wood project will be finally used. In other words, if a wood project is created in a studio with a dry environment and then moved to another location, one with — let’s say — high humidity, you could have problems because the wood will physically expand as it absorbs moisture from its new environment. Depending on the type of wood project this could cause problems with gluing (especially around joints and cracks), drawers, doors, and joints that don’t fit properly, and even warped, cracked finishes.
Keeping Wood At Its Desired Moisture Content
Once the wood you’re planning on using in projects has reached its EMC, it should be monitored to make sure it doesn’t continue to gain or lose moisture. This is important because it takes time to restore wood to the correct moisture level and creating projects from wood that isn’t at the correct moisture content is a waste of time and money. Also, as noted above, it could even hurt your reputation. Proper handling and storing will assure that this doesn’t happen. However, what if your conditions are not correct and need to be corrected?
When Wood Is Too Dry
Wood (including components, parts, and final products) that’s too dry — that is, under 5% moisture content — is difficult to restore to its previous quality. If this happens, the best solution is to place the wood in a room where the relative humidity is about 1-2% above the desired EMC. You should also have several fans stirring the air and blowing it across the surface of the wood. You’ll then need to wait for as long as it takes for the moisture content to adjust. This might take several weeks or even longer.
When Wood Is Too Wet
Wood components or parts that are too wet can often be re-dried successfully. (It’s difficult to successfully re-dry a finished project if the high moisture content is a result of poor storage conditions.)
Place the wood in a warm room where the relative humidity is one or two percentage points less than the desired EMC. A little heat will speed up the drying process. The wood will need to remain in this room until the core has reached the desired moisture content.
Wood’s hygroscopic properties mean that it should be stored in conditions very similar to those where it will be finally used. Failure to do this could result in moisture-related deformities. For more information related to this, we encourage you to read Acceptable Moisture Levels in Wood – Knowing the Moisture Content. It’s an in-depth article that serves as a kind of primer on moisture content in wood.
How to Store Unseasoned Lumber
Wood that has been freshly sawn has a lot of moisture in it. If you leave it in a warm, dry environment the moisture will, over time, evaporate. However, a special wood-drying kiln is usually used to speed up the process. Most of the wood you see for sale has been kiln-dried.
Indoor air drying without a kiln
If you have a warm, dry environment it’s possible to season wood without using a kiln…
Horizontally stack and sticker the unseasoned wood. Stickers are small pieces of dry wood (about 1” x 1”) that are evenly spaced (no more than 16 inches apart) between the wood so air can circulate around it. The stickers should also be lined up vertically so you don’t end up with wavy lumber. Green wood is very pliable and will easily bend if you’re not careful.
Is it possible to air dry lumber outdoors?
It’s possible, but not recommended unless you live in a warm, dry environment. Most areas are simply too humid to air dry lumber outside successfully.
How to Store Seasoned Lumber
Wood that’s already at the desired moisture content should be stored in the same location where it will be used. Or, it can be stored in a place with similar conditions to that of the place where it will be used. Of course, you’ll need to control the moisture in that environment to make sure the wood stays at the desired moisture content.
If you have enough space you can store seasoned wood horizontally. In fact, for long term storage and for very thin pieces of wood (less than ½-inch) this is the best way to store it. However, don’t worry if you’re living in tight quarters. Seasoned wood can be stored vertically indoors without any problem.
Storing dry (seasoned) lumber horizontally indoors
If you’re going to store seasoned wood indoors horizontally, make sure it’s well supported. Placing support boards every 16-18 inches will keep the wood from bowing.
You don’t need to use stickers when you store seasoned wood indoors because the wood is already dry and does not need air circulation.
Storing dry (seasoned) lumber vertically indoors
If you don’t have space for storing seasoned lumber horizontally, don’t sweat it. You can store it vertically without any problem. Just make sure the storage system you use is raised slightly off the floor so that air can flow underneath it. The ground might not be as dry as it looks.
Also, make sure the vertically stored lumber is supported at both the top and the bottom to prevent bowing. Finally, small pieces of wood can be stored in a lumber cart. You’ll be able to find instructions online for how to make one.
Why You Should Use a Wood Moisture Meter
Even if you buy your kiln-dried wood from reputable suppliers, there’s still no guarantee that the wood was at the correct moisture content when it left the mill. Even if it was, it might have been stored in an environment that caused the wood’s moisture content to change. If that happened, you wouldn’t know unless you had a quality moisture meter and were able to test the moisture content of the wood yourself. Therefore, investing in a good, reliable moisture meter is something like buying insurance. It enables you to measure moisture content in wood in order to keep your projects, your reputation, and your wood investment safe.
Major wood products manufacturers know what they’re doing. That’s why they use handheld moisture meters and sometimes large in-line moisture measurement systems on their conveyors in their day-to-day operations to measure moisture. A quality moisture meter is a critical tool for anyone who works with wood.
Advantages of a Pinless Wood Moisture Meter
There are two types of wood moisture meters: pin and pinless. They both come with a variety of features and prices to fit most any hobbyist’s budget. However, many professional woodworkers prefer pinless wood moisture meters for the following reasons…
- They don’t leave holes in the wood as pin meters do.
- They allow you to scan many board feet in just seconds. Compare this to the time-consuming process of taking multiple moisture readings with a pin meter.
- They usually don’t require corrections for wood temperatures above or below 70F, as do pin meters.
- Moisture readings aren’t affected by the orientation of the grain.
- They’re easy to use. Just turn the device on and start scanning.
Wagner Meters manufactures some of the most reliable and accurate pinless moisture meters on the market. We have a number of non-damaging digital wood moisture meters that can easily fit on any hobbyist’s tool belt.
Hobbyists can choose from any model in the Orion® line of wood moisture meters. They all come with an industry-leading 7-year warranty.
Orion pinless wood moisture meters can be used on the most common temperate softwoods and hardwoods, as well as denser tropical species.
Build your wood projects as the pros do. Use a quality moisture meter and avoid common, moisture-related woodworking problems.
As Sales Manager for Wagner Meters, Ron has more than 35 years of experience with instrumentation and measurement systems in different industries. In previous positions, he has served as Regional Sales Manager, Product and Projects Manager, and Sales Manager for manufacturers involved in measurement instrumentation.