If you have ever tried to make a campfire with wet wood, you were likely greeted by a bunch of smoke and non-existent flames. We all know that wet wood doesn’t catch fire. But making a fire isn’t the only time you have to worry about moisture levels in wood. All wood has some level of moisture in it, even when it hasn’t been sitting out in the rain. The level of moisture has an impact on the final result for a few reasons. Before we get into specifics about how moisture levels will affect a final product, let’s learn some basics about the moisture in wood.
Trees need water to live, and much of that water lives in the trunk of the tree. When trees are first cut, they are said to be in a ‘green’ state where they are saturated with moisture. The trunk of the tree contains both free water, which is trapped in the pores and cracks of the wood itself as well as bound water, which is water that has saturated the cells of the wood.
After a tree is cut, the wood begins to lose moisture. Free water will naturally leave the wood, but bound water needs a little extra help. After the free water evaporates from the wood, the wood reaches what is called a fiber saturation point (FSP), where the only remaining water is that which is trapped in the cells and fibers of the wood. Once the wood loses water beyond the FSP, it begins to shrink its size and is now in a state of drying, rather than its ‘green’ state.
Once the drying process begins, the wood will continue to dry to match its relative humidity - or the humidity levels of the surrounding air. This means a piece of wood in the Nevada desert will naturally dry with less humidity than the same piece of wood in Florida.
To make the wood dryer than the relative humidity, you will need to use a kiln (or purchase kiln-dried lumber to work with). Think of buying kiln-dried wood like buying pre-washed jeans. Jeans shrink when you wash them, so even if they fit in the store dressing room, but after you run those bad boys through a laundry cycle, they might lose an inch or two of length and shrink in the waist. To avoid upset customers who no longer fit into their brand new jeans, some stores advertise their jeans as pre-washed or pre-shrunk so the size you buy is the size they’ll stay. Because wood shrinks and potentially even cracks as it dries, then buying kiln-dried wood will prevent any moisture-related surprises like warping and cracking after the finished product is proudly placed on the shelf.
The amount of moisture in a piece of wood is called the moisture content, or MC. This is a percentage based on the weight of water in a piece compared to the weight of the actual wood. Typically, woodworkers want their wood to have a MC between 6 and 9 percent. The only way to determine the amount of moisture in a piece of wood is to use a high-quality moisture meter. Using a moisture meter to test the MC of wood is especially important if you are using your own kiln to dry wood.
Moisture meters, like the Lignomat Moisture Meter we offer here at our woodworking supply store, work by sending a small electric current through metallic pins and into the wood. Moisture meters typically have two small pins that you insert into the wood. These pins attempt to send an electrical current to one another. Wood does not conduct electricity, but water does. This means that the less water there is present in the wood, the more resistance there will be between these pins. If there is a higher content of water, the electrical current will travel with greater ease and send feedback of a higher MC.
However, reading moisture in wood doesn’t only have to be reserved for woodworking. You can also test moisture levels in the drywall around your home if you suspect a humidity issue, ensure your lumber is dry before you work on your next construction project, or you can check levels in your shed or fence to see if your structures are in danger of rotting.
When it comes to essential woodworking supplies, a moisture meter can be a lifesaver. This is especially true if you are selling your finished products or giving them away as gifts. The last thing you want is to get a call several months or years down the road from someone saying the beautiful wood turned bowl you sold them endured a big crack. The Lignomat Moisture Meter has 42 settings to correct for things like tropical and domestic wood species, temperature, laminates, and more. Take the guesswork out of woodworking with a quality lumber moisture meter from Long Island Woodworking Supply.
