Large timbers can give your floor, deck or other wood structure a charming, rustic look. It’s no wonder they’ve become so popular. But 12×4, 6×6, and 12×12 pieces of timber pose some unique challenges. One of the main issues which people notice with larger pieces of timber is that the wood has a tendency to develop noticeable cracks. This cracking, also known as checking, is extremely common.
Several questions arise in response to this phenomenon. For example, why does the wood check? Do some wood species check more severely than others? What, if anything, can be done to avoid this checking tendency? Is the checking in large timbers something a lumber dealer or consumer should worry about? Will the checks in the wood be permanent? Lastly, should the checks be filled in, and if so, with what material? In this article series, we’ll attempt to address each of these common questions and alleviate concerns about this topic.
Why Do Large Timbers Check?
First, we’ll tackle the foundational question. Why does timber have a tendency to check? It can happen to practically any type of wood. Checking is a natural response of the wood timbers to the different amounts of moisture that are retained in the inner layers as opposed to the outer layers.
Normally the outer layers of wood become dry more quickly than the better insulated inner layers. Naturally, the larger the board the greater the difference one would expect to see between the moisture level at the outer layers than at the inner layers. The greater the difference in moisture content in these layers, the more significant the size of the checks that will tend to appear in the timber. Checking is extremely common in large timber. If you don’t see checking in a large board over time, you may actually want to check and see if the core is rotten.
Do Some Wood Species Check More Than Others?
The answer to this question is yes. The less-dense the species of wood is, the more it will tend to develop large checks. Timber that comes from fir, for example, can develop large checks that make a loud cracking sound when the cracks suddenly appear. If someone isn’t aware of this tendency, it can be quite shocking to see or hear it happen. People may be worried about the structural integrity of the building. When the pressure between the wood layers builds up, it will finally give way and the timber will develop a check.
In dense woods, such as Ipe or some of your other tropical hardwoods, the checks that appear will be smaller in size, though there may be many of them. The checks in denser wood species also don’t tend to go much past the surface of the wood. These checks tend to be less noticeable than those in less dense species of wood.
As you are probably gathering from the information presented so far, checking is a natural process you can expect to happen, especially when you’re working with large boards. In our next article, we’ll consider some of the other common questions people have about lumber checking.