Q: Explain what is meant by setting the pitch. How do we do this?
A: Many softwood species, including most of the pines, have pitch that is liquid at room temperature. Actually, pitch is made up of a variety of chemicals and only some of them are liquid at room temperature. These liquid chemicals in the pitch will bleed, dip, and move through various finishes and overlays, resulting in a sticky, ugly spot or two on the wood product or on the floor.
During drying, the wood is heated to 180 F or hotter for 24 hours or longer, depending on lumber thickness. (Most, but not all, kiln schedules go to 160 F or 180 F as part of the regular schedule, so no special heating cycle is required.) This high heat allows the most volatile chemicals in the pitch to be driven off (evaporated). The ones evaporated are also the chemicals that would be liquid at room temperature, so this heating eliminates the pitch bleeding problem at room temperature. The pitch remaining in the lumber is hard at room temperature. Note that the pitch remaining in the lumber can soften and flow if the wood is heated over 130 F, including heating during machining or finishing.
A few people set the pitch at 160 F, but I do not believe that 160 F is as good as 180 F. Obviously, lumber air dried only and not kiln dried will have a high risk of pitch bleeding.
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