by Gene Wengert
wooddoc@uwalumni.com
Q:I am having a problem with checking in our veneer. The problem seems to come in batches of veneer, while other batches are perfect (same species and supplier in all cases). When we have the problem, we might see a few checks before finishing, but most of them develop after finishing... a few hours to a few days. When we have the problem, it might be as many as 20 percent of the pieces. Can you shed some light on this swelling closed. Likewise, when a and suggest what we can look at? water-based adhesive is used, the A: moisture will swell the cracks closed. In almost all cases, When the moisture from high RH or checking in veneer occurs from glue leaves the wood, such as during the manufacturing when heated in the finishing process (including drying) of the or when stored in a dry location, the veneer. Once the veneer is wood veneer will shrink, creating dried, it is twice as strong stress. This stress can easily open as when it was green existing checks, but the stress level and so it is unlikely that is too low to open new checks in the forces can develop that will initiate veneer. Often when the check opens, new cracks. So, the cracks you are it cracks the finish. Finish cracks are seeing are old cracks that are opening often very obvious, appearing as white after finishing. lines. The cracks can develop when the So what can you do? I suggest that veneer is cut. They can develop when you develop a test where you expose Gene Wengert, “The Wood Doctor,” has the veneer is dried. In both cases, a few pieces of newly received veneer been training people in efficient use of wood for the past 35 years. He conducts many there are specific manufacturing to a little heat and low humidity ( 90 short courses and has written hundreds procedures to avoid such cracks. After F and 35 percent RH perhaps). If the of practical articles and books covering drying, it is common to find that the cracks are there, they will open. You all aspects of converting logs into lumber cracks are tightly closed and are nearly may have to use good lighting to see and lumber into finished products. He is impossible to locate. This is especially them, however. presently an extension specialist emeritus at the University of Wisconsin-Madison. Fax true if the humidity in shipment and It is often found that the cracks your questions to him at 847/390-7100 or storage is 50 percent RH or higher; are only on one side of the veneer. e-mail to wooddoc@uwalumni.com. this humidity will result in the checks This side is usually called the loose
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