Setting Pitch in Southern Yellow Pine
You have to heat the wood to 160°F to set all the sap. Otherwise it will ooze out, even through shellac or other sealers. February 9, 2008
Question
I have some air dried pine (I assume it is SYP as I live in southern Louisiana) that I cut 6 months ago from standing trees that had been dead about a year. About 3 months ago I built a wheel chair ramp out of the wood and now sap is beginning to ooze from the boards in a few places. These boards are in direct summer sun all day long on the ramp. I have recently moved some of the lumber into my air conditioned shop and planed it to thickness, with the thought of building some bookshelves for the house. At present they show no signs of sap problems. If I seal the boards with shellac and then paint them, will I have sap oozing from the boards in a few months or years time? Would polyurethane be a better finish - or is the sap problem inevitable?
Forum Responses
(Sawing and Drying Forum)
From contributor D:
The sap is running on the wheelchair ramp because the pine boards have not been heated to set the sap, to dry the sap out. There are 1000's of chemical compounds in SYP sap and each has a melting point, sap running. If you heat a SYP board up to 100°F the sap is set to 100 degrees, and all the chemical compounds with less than 100°F melting point will not run. Industry takes SYP boards up to 160°. Assuming you don't have access to a kiln, I'd put the boards up in your attic for a week or so and the sap should be set, up to 110~140°F. At that time I'd build the bookshelves and for a backup, I'd seal the board with shellac as a sealer coat. Be advised, while machining the lumber you could get sap, pitch due to exceeding the attic temp. I like to spray my saws with Pam cooking spray prior to sawing SYP. Pam helps in reducing the amount of pitch on my tools from SYP.
From Professor Gene Wengert, forum technical advisor:
The sap will eventually ooze through shellac and paint
From contributor T:
Gene, contributor D is saying that the sap can be set by exposing it to certain temperatures, but you wrote it will eventually ooze through - is he wrong? Sounds like a nightmare of woodworking projects, handicapped with sticky wheels and books that won't open.
From Professor Gene Wengert, forum technical advisor:
You need to heat SYP to about 160 F or hotter to get rid of the sap that is liquid at room temperature. I was answering the first question; contributor D is correct.
From the original questioner:
Thanks. It's not what I wanted to hear, but it is what I suspected. I think I have some nice oak or cypress that would make excellent shelves, and I'll leave the pine for another day.
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KnowledgeBase: Knowledge Base
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KnowledgeBase: Primary Processing: Kiln Operation
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