Stopping Sap Oozing From Knotholes in a Pressure-Treated Deck Q Is there anything that can be done, short of tear-out and replacement, to prevent the knotholes in pressure-treated pine decking from oozing on hot days? A Paul R. Fisette, director of the building materials and wood technology program at the University of Massachusetts in Amherst, responds: The sap in the knotholes softens and begins to run as it is heated by the sun. Sap is composed of liquid and solid materials. If it is heated to 160°F while it is being kiln-dried, the volatile liquid substances will flash off, leaving