How To Seal Knots In Wood
Don't overlook the importance of sealing knots in wood surfaces. Bleeding and yellowing can occur quickly through wood surfaces that aren't sealed and maintained properly. Prevent bleeding by sealing with Polyprep.
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Sealing knots with Polyprep
Polyprep 205-112 sealant is a transparent light and refined pure shellac-based coating. It keeps the knots and veins of softwoods like pine, spruce and fir from bleeding. However, it cannot keep the resins in such woods from sweating. Such resins may sweat under heat or sunlight. Resin can sweat through paint and cause it to turn yellow within a few months. This is most likely to occur with darker paints that absorb more heat than do lighter paints.
Polyprep 205-112 sealant is also used to close the pores of wood, thus reducing the number of applications needed for a good appearance. Shellac is the best sealer. Polyprep 205-112 sealant should not be used with urethane-based varnishes.
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Checklist
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Turpentine or Polyprep 875-104 thinner
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Methanol or Polyprep 771-140 brush and roller cleaner
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Scraper
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Medium and extra-fine grades of sandpaper (220 to 320)
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Brush, pad
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Heat gun
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Shop vacuum cleaner
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Polyprep 205-112 Sealant
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Sealing knots in wood
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1. Scrape away excess resin.
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2. Heat knots with heat gun and again scrape away excess resin.
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3. If knots are tacky, wash surface with turpentine or Polyprep 875-104 thinner.
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4. Sand rough spots and vacuum up dust.
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5. Apply thin, even coat of sealer.
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6. Let sealer dry completely (1 hour).
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7. Repeat steps 5 and 6 as required. Two to three coats are necessary in some cases in order to seal knots. The sealant will then have a glossy aspect.
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8. Clean tools immediately after use with methanol or Polyprep 771-140 for brushes and rollers.
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9. Apply a solvent-based primer coat or GoPrime 190-135.
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