Welcome to our introductory article in this series all about the importance of moisture meters in the lumber industry. Anyone who works with lumber knows the dangers of wood being too wet or too dry. Managing moisture content in lumber is essential. Years of experience, high tech tools and premium-grade lumber will not make a difference if moisture content goes unchecked. Even a five percent change in the moisture levels of wood can cause between one and two percent movement or change in the wood itself. This can be the difference between whether lumber is usable for a particular project or not.
From the mill or dry kiln to the carpenter or woodworker, moisture must be controlled at every step of the lumber’s journey. This is especially important when building furniture, door and window frames, floors, or even carvings. Delmhorst Instrument explores why moisture content in lumber must be monitored with effective, reliable moisture meters, and the challenges that ensue if it is not.
Lumber: A Naturally Wet Product
Wood, by its very nature, is a naturally wet product. Living trees contain a huge amount of water, which travels through the whole plant as sap. When trees are first felled, the wood is called “green” and needs to be dried or seasoned before it is usable by any industry. Eventually, the moisture level in the wood balances out with the prevailing environmental conditions. However, the wood doesn’t ever completely stabilize. Even after the wood has been processed and made into furniture or other consumer items, it continues to be affected by ambient moisture.
This is particularly challenging for the technicians and experts that work with wood every day. Wood that is too wet while being worked on will inevitably dry out somewhat upon placement in its final environment. This can lead to shrinkage, creating undesirable defects and so unusable. .
Think of a window frame. It needs to fit exactly into the opening created for it, to provide protection and insulation for the building. If the moisture level of the wood is in sync with the environment, then only minimal changes in the wood should occur. These can happen as a result of changes in weather, or a sudden change in humidity due to condensation or other internal factors. However, if the wood used for the window frame has a much higher moisture content than the environment, it will, over time, lose moisture and shrink. This leaves the building with a window frame that could develop gaps or cracks, creating drafts and even posing a health and safety concern.
Checking the Moisture Content in Lumber
The only fast, accurate and reliable way to monitor the moisture content in lumber in the field is with a quality moisture meter.
Moisture meters use a small electrical current or an electromagnetic sensor to accurately test the moisture content in lumber. There are two primary types of moisture meters: pin-type meters and pinless meters. The pins in pin-type moisture meters are inserted directly into the material. A current runs between the pins, and the resistance to that current tells the meter the moisture content of the wood.
High-end moisture meters, such as those in Delmhorst’s Navigator™ line, come with a range of settings that allow you to input settings for different wood species, temperature and electrode type - all factors that affect the meter accuracy.
Pinless meters have a sensor that’s simply placed on the wood’s surface. This type of moisture meter uses electromagnetic wave technology to assess the moisture level. All quality moisture meters should meet industry standards to give the user confidence in the results and in some cases, make them safe for use.
Acceptable or target moisture contents depend on the final use of the wood and is also climate driven. So it is critical to know the EMC or equilibrium moisture content where you are working and also where the wood will ultimately be in use. Fine furniture, for example, should be dried to 6-9% in most areas of the US, with little variation among pieces between the shell and core. As wood drying and processing usually starts at moisture contents well over fiber saturation (approx 30%) the best way to ensure the wood is dry enough is with a reliable and accurate moisture meter.
Problems Caused by Unacceptable Moisture Content Levels
There are a variety of issues caused by failing to monitor the moisture content in lumber. If the wood is too wet it may:
- Shrink after it’s been processed
- Warp, which is where part of the wood dries out and causes the finished product to change shape
- Develop mold or other microorganisms that damage the wood
- Cause health and safety concerns
Working with wood when it is too dry could also be an issue for the following reasons:
- Too dry wood may swell when installed in an area with a relatively high environmental moisture level
- Wood that swells can cause safety issues, such as a fire safety door that starts to stick within its frame
- If wood suddenly dries out it can also split, which can cause both aesthetic and safety issues
- Over-drying wood can make it brittle and the wood may even lose some of its structural integrity
Hopefully, it’s clear by now that, without a quality moisture meter, anyone who works with wood is taking a huge gamble. As well as causing lumber to warp, shrink, or swell -- and spoiling the appearance of finished projects -- the unacceptable moisture content in wood can even cause products to be unsafe or not fit for purpose.
Speak to Delmhorst Instrument about the right kind of moisture meters for your application. In our next article, we’ll look more closely at how reliable, high-quality, and cost-effective moisture meters meet the needs of the lumber industry.