Beetles in Floor Joints Best Handled by Pro

QUESTION: The 65-year-old house I recently purchased has some bad floor joints. New wood framing members were placed beside the old. The old floor joints are peppered with 1/8-inch holes. They are thoroughly tunneled full of wood dust.

I tore down some of the worst floor joints with my hands and saw several insects that looked like silverfish. What can I apply to kill the insects and prevent further damage? Someone recommended coating the framing with used motor oil.

ANSWER: Your description sounds like the work of powder post beetles rather than silverfish. Silverfish, though a common pest, do not eat or damage wood. Powder post beetles, however, do.

The beetles lay their eggs in cracks and crevices in the surface of the unfinished wood. After the eggs hatch, the larvae feed and tunnel through the wood, reducing it to a powdery residue. Just before emerging from the wood, the newly formed adult beetles chew small round holes (1/32nd- to 1/8-inch in diameter) in the wood surface. Shortly after emerging, the beetles mate and lay eggs, occasionally depositing them in the opening of an old exit hole, and reinfesting the same piece of wood.

Those joints that have extensive damage have been infested by several generations of powder post beetles. It’s very possible that the floor joints were infested before being used in constructing your house.

Definitely do not use motor oil to coat the joints. The motor oil would create a fire hazard and produce unpleasant odors in your basement.

Controlling active infestation is best handled by a licensed pest control operator using either liquid treatment or fumigation. Both methods present potential environmental hazards and should be administered by a professional. While this may be costlier than attempting the job yourself, it should also give you a guarantee that the beetles will have been destroyed.

You should also check to see that the replacement joints have not become infested from the older ones beside them. If they have, then you may have to replace these as well, but only after you are certain that the problem has been solved permanently.

Polyurethane Best Finish for Wood Sash

Q: I have wood-sash, double-glazed windows that have to be stained and varnished. In the cooler parts of the house, condensation collects on the panes and drips onto the horizontal parts of the sash. Now the finish is starting to crack. What is the most water-resistant finish that can be applied to the sash?

A: For the best protection, the wooden sash should be coated with a polyurethane finish. Before applying such a finish, you should strip the sashes, sand them thoroughly and then wipe them clean with a tack cloth. When refinishing, apply the polyurethane so it covers about 1/32nd of an inch of the glass pane. This seals the joint between the glass and the wood.

For further information on any home problem, write to Popular Mechanics, Readers Service Bureau, 224 W. 57th St., New York, N.Y. 10019.