Battling powderpost beetles plus more FAQs
September 20, 2023 | 10:46 am CDT

Q We found some powderpost beetles (PPB) in some paneling we installed when doing a kitchen. They were identified as lyctid PPB, which are the ones that get into dry hardwoods. We had a treater come and apply borate to the wood paneling that was already installed. Now, about a year later, we are seeing some new holes and powder. Can it get into the cabinets? What do you think?

FDMC Wood Doctor
Borate is commonly used to combat lyctid powderpost beetles in lumber.

A The answer below is specific to your situation, but the ideas apply to most other cases of lyctid PPB.

Borate is very effective on killing the insect, but only if the insect comes in contact and eats the borate. I suspect (an educated guess) that the borate treatment did not diffuse all the way through the wood. That is, the borate is in water and, because the water carries the borate into the wood, the water probably evaporated before the water carried borate to the back side of the paneling. That is, the treatment was only on the front. So, there were some insects that laid eggs on the rear and these were able to survive as they did not come in contact and eat the borate near the front surface.

Unfortunately, everyone is probably going to blame everyone else and no one will accept responsibility. A lawyer is expensive. Odds are that the supplier gave you wood with the beetles in it. What is really helpful when figuring out responsibility is if you have the exact dates when the paneling was delivered and you and the homeowner took custody, when it was installed, and when the beetles were first noticed.

With respect to the cabinets getting infected, the finish coating on the cabinets is usually sufficient to prevent the entry of the insects. Are the backs finished or are they raw wood. If not finished, then there is a high risk.

My suggestion is that you will have to remove the paneling. (The supplier might agree to supply you with new paneling at no cost to you.) Then, take the cabinets off the wall. Then, vacuum up the debris. Any hardwood moldings will also have to be removed. Then, treat everything with borate, front and back with enough water and wetness to assure deep penetration of the borate. Certainly, this is a lot of work for you, especially as it is likely not your fault.

Instead of borate, you could also heat treat the wood, heating the wood through and through to 133 F for a short time — one hour will work. The heat kills everything at this moment, but borate (safe for humans) provides lasting protection into the future.

Q I am a small shop woodworker with two employees. I thought it might be a good idea to purchase a small sawmill and saw my own wood, dry it, and save money. I just want your readers to know that this is not the best idea, as only 2/3 of the lumber I saw is worth going into my manufacturing shop. The rest of the lumber, low grade, is hard to get rid of at a reasonable price. Do you agree with this?

A Your experience is indeed valid. It is very difficult for a forest products company making furniture, cabinets, etc. to operate a sawmill for this reason. On the other hand, having your own mill assures you of a supply of lumber. Even though low grade lumber has a poor yield and takes longer to cut into usable pieces, there are many situations where using low grade is indeed profitable.

Usually a sawmill has to give the sawdust away. The outside slabs (referring to the round on one side outside sections of the log) can be cut into short pieces and donated to a local community agency that provides firewood to “poor” people. This donation likely has tax benefits for you.

Q We have a new lumber supplier. He provides 4/4 oak and maple that is kiln dried and planed or surfaced on two sides (S2S). I had learned that when grading hardwoods, we look at the worst of the two sides, but this new person says that he grades from the best side. Comments please.

A When doing S2S, rules state that when grading after surfacing, grading is from the better side. All the regular rules apply.

The reason for grading S2S from the better side is that S2S lumber does show up more little defects than we see in rough lumber.

Your supplier could grade before planing and then tell you that is what he did. Essentially, you bought rough lumber (had legal title to it) and then he made your lumber S2S with an added charge. This process makes any regrading or speculation of the grade of the rough lumber impossible to determine.

Sometime S2S lumber will be graded from the best side, but little imperfections are ignored. This change is called WHND (worm holes no defects).

Q I heard you give data on the reduction in yield due to part width and thickness. Can you repeat them?

A We have a lot of numbers, so here is a summary.

THICKNESS. Compared to 4/4 yield in the rough mill, 5/4 yields are 5% less with the same grade of lumber; 8/4 is 8% less.

WIDTH. If the typical width of a cutting is only 2 inches wide, cutting random width increases yield by 4%; cutting only 4 inches wide, decreases by 15%; and cutting only 6 inches wide decreases by 37%.

LENGTH. If the shortest length you cut from #1 Common red oak is 30 inches, the yield is 64%; if 20 inches, the yield is 69%; if 10 inches, the yield is 73%. (This is one part of the benefit of fingerjointing short pieces.)

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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 45 years. He is extension specialist emeritus at the University of Wisconsin-Madison.