Dealing With Loose Knots: Wednesday's Word Of The Week

The lumber used in glulam and other wood products is cut from the trunks of trees. Being a natural product, there are many unique characteristics which can affect its strength and appearance, both positively and negatively. One of these characteristics is knots, which are the locations of former tree branches. Knots interrupt the primary wood grain, and therefore reduce the strength capacity of wood. This is accounted for in grading, where #2 material is allowed to have more or larger knots than #1 material.

Where knots are small or well fixed in the wood, they add an interesting visual characteristic. But "loose knots", which are typically larger and are not well bound, can fall out of the lumber itself, during glulam fabrication, or later. Most would consider this a negative characteristic, so this is one of the defect types that is removed and plugged on the glulam surface. Large, loose knots are much more common in Douglas Fir than in Southern Yellow Pine.
*Wednesday's Word Of The Week is a feature on Unalam's Wood Times Blog. Each Wednesday our structural engineer, Rik Vandermeulen, will discuss a new term associated with glulam manufacturing. He will do this until we run out of words. If there is a timber or glulam term that you have heard of and want to know more about, let us know in the comments.