Step 1
Bring 1 gallon of propylene glycol to a boil, and then add 4 pounds of laundry soap and 3 1/2 pounds of boric acid. Stir the liquid constantly until it thickens and homogenizes.
Step 2
Reduce heat on the stove after the compound thickens, but continue to stir for a few minutes longer. Remove the mixture from the stove and allow it to cool to a lukewarm temperature.
Step 3
Carefully pour the lukewarm mixture into a plastic 1-gallon container. Wear latex gloves to protect your hands from the chemicals. Cap the container with an airtight lid, and use the concentrated compound within a few weeks for the highest level of effectiveness.
Step 4
Dilute the mixture with water (remember, it is a concentrate) before applying to wood. Paint the diluted liquid onto the wood surface using a paintbrush. Allow the wood surface to dry completely before use.