Wagner Meters proudly presents this Wood Moisture Measurement webinar series by Charlie Phillips from Pittsburgh State University.
Charlie covers several crucial, all-important topics related to wood moisture content. Anyone who works with wood in any capacity must have a thorough knowledge and understanding about wood and its close relationship with moisture in order to prevent costly mistakes with the finished wood product.
What is Wood Moisture Content?
Now that we have a definition of wood moisture content, how do we measure the amount of moisture content in a piece of wood?
It’s universally understood that the success of any project involving wood – from wood flooring to building fine furniture – depends on taking accurate readings of the wood’s moisture content. Here are some hints and tips:
- Read your wood moisture meter manual.
- Call Wagner Meters at (800) 634-9961 for instructions.
Once you know how to measure the wood moisture content, then you can evaluate if the wood moisture content is correct. Incorrect moisture content – if left untreated – gives way to a multitude of problems. Moisture content affects wood size across the grain as well as with thickness and width because wood does not shrink appreciatively along the grain; that is length-wise, even with large moisture changes.
How does Moisture Content Affect Products?
If the wood has not acclimated to its environment and adjusted to the correct moisture content, this should be corrected.
How do I correct Wood Moisture Content?
Additionally, there are some basic facts about the relationship between wood and moisture. Most of the important properties of wood depend considerably on its moisture content, and the moisture levels present in wood depend upon the environment. Even if the wood is kiln-dried, it does not eliminate future moisture levels from changing within the wood.
The Relationship between Wood and Moisture
A question that’s often asked is: What affects the time it takes for the final equilibrium value to be reached?
Moisture content in a piece of wood doesn’t change unless the EMC and the moisture content are not equal. It’s important to understand the relationship of EMC and moisture content.
Let’s now take a look at the relationship of relative humidity and moisture content. The relative humidity of the air surrounding a piece of wood determines the moisture content of the wood and the equilibrium with its environment. In other words, wood will lose or gain moisture until it is in equilibrium with the humidity and temperature of the air. It’s important to note that temperature does not significantly affect the moisture content of the wood and therefore, temperature does not make wood shrink or swell significantly either.
The Relationship between Relative Humidity and Moisture Content
Lastly, it’s important to understand how much the moisture content of wood components and wood products changes from the time they initially are manufactured until the time the wood is being used in a customer’s home or office. In other words, how much does the wood moisture change before achieving its final moisture content?
Moisture Content from the Manufacturer to the End User
When wood is taken indoors, it interacts with the air around it, including the water vapor (humidity) in the air. We know that the wood being used in most offices and homes in North America has an average interior EMC (Equilibrium Moisture Content) of 6% to 9%. As a rule of thumb, wood technologists say that this 6% to 9% EMC comes from a relative humidity of 30% to 50%. Of course, this varies with geographic location – that is, is it a coastal location, an inland location, etc?
The correct moisture content for raw materials coming in to a manufacturing facility as well as for wood products during manufacturing, storage and installation, depends on the ultimate in-end use EMC for the product.
The typical desired average moisture content for lumber, parts and components intended for interior products, such as a wood floor, is 6% to 7%. This is especially critical for wood flooring professionals who strive for a successful installation and who want to avoid warranty work.
Since wood is a variable material – with no 2 pieces identical – there will always be some small variation in moisture content under 1% in individual pieces exposed to the same EMC. As a general guideline, the ideal difference between the moisture content of wood and the EMC of air is 2% moisture content.
In order to achieve better moisture content uniformity, more effort is required during kiln-drying as well as better dry lumber storage in handling – both of which add to the price of the lumber and wood components.
The key to successful control of moisture content begins with the kiln operation. Then once the lumber is kiln-dried, the lumber must be stored at the correct EMC to prevent undesired changes and moisture content.
Storing Wood at the Correct Moisture Content or Equilibrium Moisture Content (EMC)
When it first arrives, kiln-dried lumber in process parts and manufactured wood components must be stored at the correct EMC to prevent undesired changes in moisture content.
Because wood components are much smaller than lumber, they have more surface area per volume and the grain is more exposed than lumber. As a result, you need to be aware that wood components will change moisture content much faster than lumber if the EMC of the air isn’t equal to the moisture content of the component.
A critical element in controlling moisture content in wood components involves controlling the EMC in the manufacturing facility; you want the EMC to be as close as possible to the EMC in a customer’s home or office.
Wood products that are intended to be used indoors should never be stored outside or in an unheated building or shed.
Well, this concludes our special presentation on wood and moisture. Before signing off, let me leave you with one solid bit of advice: Spotting any potential moisture problems, and taking the proper steps to avoid them, is the key to your success for any wood flooring or woodworking project.
On behalf of Wagner Meters, I’m Charlie Phillips. Thanks for watching.