Q. Once in a great while, we see a white paint turn dingy in small regions on a panel. Oftentimes this dinginess shows up a month or two after painting. What is this?

Answer. I see this only once or twice in a five-year period. We do know one cause for this, but there may be others.

There are anaerobic (no air) bacteria found in the wood of a living tree from time to time and associated with ring shake and bad odors. These bacteria also weaken the wood, leading to excessive checking in drying. Additionally, these bacteria create fatty acids in the wood that have been shown to migrate through the wood slowly after a product is manufactured creating dinginess in white finishes. So, it is my guess that this is what you are seeing.

So, did you notice during manufacturing or can you now when you put water on the stain any unusual smell? If you do, then this confirms the diagnosis. Even if you cannot smell any difference, it still can be these bacteria and their fatty acids.

Unfortunately, this is something within the living tree that we, as manufacturers, can do little about if we do not detect it (ring shake, odor, discoloration) in the manufacturing process. Drying or other sources of heat have no effect. It seems to be related to trees from a particular logging site, so the problem disappears when trees from a different logging site are processed.

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.

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