Mix in a spray bottle 70 percent denatured alcohol (ethanol) and 30 percent water. Spray a sharp knife with the mixture to sterilize it. It is extremely important to use sterilized pruning tools when trimming oak tree bark to prevent spreading disease.
Trim 1/2 to 1 inch around the wound and at a depth of 1/2 inch. Try to create an oval shape around the wound, using a sharp knife. Spray the knife with the sterilizing mixture after each cut.
Remove the bark inside of the traced area, using your hands or a knife. Make sure the wounded area is smooth and even.
Spray the wound with the sterilizing mixture. Press a clean towel to the area to absorb the excess water and alcohol.
Check the wound to make sure that pathogens, fungal diseases or pests haven't entered the wound during the growing season.