In our first article, we discussed the tendency of timber to crack, also known as “checking.” We explained that this natural process is a direct result of the differences in moisture content between the outer and inner layers of a piece of lumber. Naturally, the greater the size of the board, the more it will tend to check. Another point we considered was how the density of a species of wood can cause it to check more or less, and that the denser the wood, the smaller the individual checks in the wood which will appear. In this article, we’ll explore some of the ways people attempt to reduce wood checking.
Can Wood Lumber Be Completely Prevented From Checking?
The answer to this question is, for all practical purposes, no. Theoretically, you could vacuum kiln dry the timbers. Then you could keep them completely out of full sunlight and only use them in a climate-controlled interior environment. Since there are rarely any applications that will meet all of these requirements, you’ll just have to accept the fact that the wood is going to experience some checking. It’s really not a bad thing, and there’s no reason to panic when you start seeing those checks appear.
Is Checking Bad for Wood?
Believe it or not, checking is actually good for timber. It’s a sign that a board is made from healthy wood. When the pressure build up between the wood layers is finally released, it can make the board stronger than ever before. So when you see those cracks you don’t need to worry about them causing your deck or wood floor to deteriorate. Nothing could be further from the truth.
Can Anything Be Done to Minimize Checking in Lumber?
This goal is a bit more realistic than the idea of completely preventing checking. Even though checking isn’t a bad thing, some people still don’t like the way it looks. Hundreds of years ago in ancient Japan, carpenters who built temples developed a technique known as kerfing. A kerf is a cut that’s strategically sawed into one surface of the timber. This kerf allows the pressure building up inside the wood due to moisture content variance to get released. This clever technique causes the wood to check much less than it normally would. Then if you place the timber into your application in such a way that the kerf is hidden, you’ll be able to enjoy the look of smooth, even timber with few if any checks.
As great as it sounds, kerfing isn’t often possible. That’s because the kerf has to be sawed into the timber just after it is cut and before the drying process begins. Large timbers typically come to the lumber yard already yard dried or kiln-dried.
There is another solution besides kerfing that can help prevent the timber from checking. We’ll take a look at this idea in our final article in this series. We’ll also mention some other helpful tips about how to handle checking in large timbers or in any piece of lumber.