Understand Logs: Checking and Cracking

We have all seen the checking that occurs in round logs, heavy timbers, utility poles, and log furniture.  Checking is a natural occurrence in wood components that contain the pith, or center of a tree. But what is the cause?  Checking, or the process of the logs cracking, happens as wood releases moisture, and normally occurs across or through the annual growth rings. It is the usual result of wood seasoning. Wood shrinks twice as much in the tangential direction as it does in the radial direction. This can be observed in the amount of shrinkage that occurs in individual pieces of wood cut from trees. But, whenever concentric circles (continuous growth rings) occur in wood, the circumference of those circles (tangential orientation) shrinks twice as much as does the diameter (radial direction). Since the circumference is shrinking at twice the rate as the diameter, something has to give. One way to visualize how the difference between tangential and radial shrinkage causes checking in logs is to consider the concentric growth rings. The line formed by each growth ring is basically a series of tangent lines, or, one continuous tangent line (in a manner of speaking). As a log dries, the length of each growth ring will shorten by a proportionate amount (tangential shrinkage). But even though the growth rings are shortening, the overall log diameter shrinks at a lesser rate (radial shrinkage). Stresses build up, and checks occur. How big will the checks become? It depends on the location within the log. The larger diameter outer rings shrink more than the inner rings, since they all lose a percentage of their overall length. Thus, the checks in smaller logs are narrower than the checks in larger diameter logs, just as checks are narrower the closer one gets to the pith.  Whenever continuous growth rings exist, the tangential versus radial shrinkage stresses will cause checking. Can checking be prevented in round wood?  Not really. So why do boards not check while logs do?  Well, individual boards cut from logs usually do not contain the pith, so these boards will not check during drying. Those boards that do contain the pith will typically check only on one side. It is important to know that we dry our wood in a large heated room for months to ensure that 99% of all “checking” is already done.  All logs are stress tested before they enter production to ensure that they will hold up to the test of weight and time.  This way when we package your log furniture you will know that you will not have to worry about the durability of the log furniture.  Not all companies do this, but you can rest assured that all rustic furniture found on our site goes through this rigorous testing process.  Your safety and satisfaction is of most importance to us. Checking occurs mainly on the surface of the wood and does not affect the structural performance or integrity of the wood. This natural process adds to the uniqueness of the pieces and lends it that certain rustic appeal that has become so popular in home and garden decor. The degree of checking will vary from product to product and from log to log.  Checking can range from very slight slivers of cracks to larger cracks running the full length of the log to the pith (middle of the log) of the wood. In either case this checking is completely normal and in no way affects the integrity of the wood or the strength of the furniture. Information above provided by our knowledge and by Merrimac Quality Log Homes.  Pictures below are of a couple pieces of my outdoor log furniture