Moisture levels of wood fluctuate from one section to another. The presence of moisture in wood can affect its workability of wood. It can have a damaging effect in many ways.
Can wood be too dry for woodworking? This is a question that gets asked from time to time. The moisture levels of wood determine how the wood will behave, especially when it begins to dry. Wood can crack, warp, and twist after delivery, which can cause much consternation if used on a critical project.
- The Dynamics of Wood Moisture
- Acceptable Moisture Levels in Wood
- How to Check the Moisture Level of Wood
- How to Use Moisture Meters
- Effects of Wood That is Too Dry
- The Importance of Checking Moisture Content of Wood
The moisture levels keep changing from the time we chop timber from trees and cut it into lumber. As the wood continues to be exposed to air, it continues to release moisture unless you seal it.
Sawmills continually monitor the moisture content of wood and try to reduce the moisture to an acceptable level. But it is not always possible. For example, during transportation, wood can either increase or decrease its moisture levels. Excess or reduced moisture levels can both have adverse results.
We usually consider wood with a moisture content between 7% and 14% as ideal for woodworking projects. It ensures that your wood remains pliable enough while working on it. If wood is too dry then it might crack or warp. Moreover, it can chip while cutting it and ruin your project.
So, you need to have adequate knowledge about moisture levels in wood, and how to monitor and control it. Working with wood that falls within the accepted moisture levels will not only protect your wood but also your cutting tools.
A lot of how you control the moisture content of wood depends on how you store it. So that is also a major consideration when handling, storing and transporting wood.
The Dynamics of Wood Moisture
Wood expands or contracts due to varying levels of moisture. You may have noticed some of your doors and windows jamming during wet weather. The jamming magically disappears in dry and hot weather.
It occurs due to the expansion and contraction of the wood due to the changes in moisture levels. If this happens to the wood that you work on, it can hamper the way your tools and machines work. It may even result in the wood getting damaged.
One of the best ways of assuring workable wood is to get pre-dried wood. This category of wood will have gone through an elaborate process involving drying in a kiln. The moisture level of such wood is typically between 6% and 8% although this can vary from one supplier to another.
By getting pre-dried wood you can avoid working on wood that has excess moisture within it. That way, you will not face issues of warping, shrinkage, or even splitting as the wood has already dried to an acceptable level.
Acceptable Moisture Levels in Wood
We consider wood with a moisture content of 6% to 8% for interior use and 9% to 14% for exterior applications. The higher moisture levels also apply if you are building structures that will be assembled within constructed assemblies.
The two factors that affect what is acceptable in moisture levels of wood are the relative humidity of the environment and the final use of your wood. Because of how these variables fluctuate, there is a certain level of flexibility on the specific acceptable moisture content in wood.
But that said, the above values can give you a sufficient ballpark figure to go with when you need to monitor the moisture level of the wood you use.
How to Check the Moisture Level of Wood
But what if the pre-dried wood you procure is TOO dry? It is therefore advisable to check the moisture level of the wood at the time of procurement. Here are the simple steps to check the moisture levels of wood:
Oven Dry Testing
It is the oldest method that we use to check the moisture content of the wood. Although oven-dry testing is a time-consuming process, it is an accurate method if you follow the correct procedures. Here is how you do it:
For this method, you need an oven or kiln. You take the initial weight of the wood. Then, place the wood in a pre-heated oven or kiln and weigh the wood periodically.
When the weight of the test sample stops changing, note the initial and final weights of the wood sample. The weight difference helps you calculate the original content of the wood. However, there are a few downsides to this method of calculation.
Firstly, it is a time-consuming process taking hours to complete the measurements. Secondly, the sample wood piece becomes unusable due to excessive dryness. Finally, you need to have a special oven that you may not have in your workshop.
Moisture Meter Testing
A more practical and instant method of measuring the moisture levels of wood is through a moisture meter. You get two types of meters – pin-type and pinless:
Pin-Type Wood Moisture Meters
The pin-type wood moisture meter is a lightweight, handheld meter with two pointed electrodes. You dig the electrodes into the wood, and the conductivity of the wood is measured.
The higher the water content, the lower the water-resistance and vice-versa. The meter is calibrated so that the resistance converts to a moisture level reading.
Pinless Wood Moisture Meters
The main disadvantage of a pin-type moisture meter is that the pins leave marks on the surface of the wood. If you want to prevent the surface of the wood from getting marked you can use pinless wood moisture meters.
A pinless moisture meter reads the moisture content of wood through a non-destructive electromagnetic sensor. The major advantage of pinless moisture meters is that they cover a large area when they scan the wood, giving a more accurate picture of the moisture content.
A perfect example of where you can use pinless moisture meters is when you need to check the moisture content of expensive hardwood floors. You wouldn’t want to damage the surface by sticking pins in it.
How to Use Moisture Meters
Pin-type Moisture Meter: You simply insert the pins into the wood. Ensure that the pins are aligned with the grain rather than across it. Now, switch on the meter and read off the moisture level that the meter displays.
Pinless Moisture Meter: This type of meter is even easier to use than the pin-type meter. Press the scanning plate firmly onto the surface of the wood. Turn on the meter and you will see the moisture reading of the wood on the meter’s screen.
Effects of Wood That is Too Dry
If the wood becomes too dry, certain undesirable things can happen as follows:
- The wood can split and crack.
- It could splinter on impact while hammering in nails or while driving in screws.
- The wood could develop cupping (concavities in wooden planks especially detrimental to hardwood floors).
- Adhesives dry more rapidly making assembly a bit awkward.
- The wood becomes prone to chipping.
- Tendency to swell in hot and dry weather.
- Extra dry wood can add extra wear and tear to the blades of your cutting tools.
The Importance of Checking Moisture Content of Wood
You have now seen how the moisture content of wood can affect the way it behaves. It can also make it difficult for you while work on it. Therefore, it is important to be aware of the moisture content of the wood to ensure that it isn’t too dry and for the best results.
Wood comes from the vascular system of the tree composed of tubular fibers. These fibers absorb water and store it. The water first enters the cell walls. On getting saturated, it enters the cell cavities.
Excessive water content in wood affects how it behaves. It opens up the possibility of mold attacks, fungus, and rotting. So, even wood that contains excessive moisture can have some adverse effects.
A freshly-cut tree may exhibit 40% to 200% of moisture. But as the tree dries, the moisture level soon drops and after processing, it reaches an acceptable level of anywhere between 8% and 25%.
Wood is a hygroscopic and anisotropic material. These two properties make it react to the presence of moisture in a variety of ways. Greenwood loses a lot of its water content on processing.
It’s important to know about the role that moisture plays in the performance of wood. Knowing how to monitor the moisture level of wool will enable you to work on wood at the right time.
You can ensure the moisture content of your wood is neither too high, nor is your wood too dry for woodworking. You will always get the best results using wood with the recommended levels of moisture in your woodworking projects.