Sealing knots

 

Polyprep 205-112 sealant is a transparent light and refined pure shellac-based coating.

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 finish. Shellac is the best sealant. Polyprep 205-112 sealant should not be used with urethane-based varnishes.

Checklist

  • Sealant Polyprep 205-112
  • Polyprep 875-104 thinner
  • Methanol or Polyprep 771-140 brush and roller cleaner
  • Scraper
  • Medium and extra-fine grades of sandpaper (220 to 320)
  • Brush, pad, heat gun
  • Shop vacuum cleaner

Sealing knots in wood:

  1. Scrape away excess resin.
  2. Heat knots with heat gun and again scrape away excess resin.
  3. If knots are still sticky, wash surface with turpentine or Polyprep 875-104 thinner.
  4. Sand rough spots and vacuum up dust.
  5. Apply thin and even coat of sealant.
  6. Let sealer dry completely (1 hour).
  7. Repeat steps 5 and 6 as required. Two to three coats are necessary in some cases to sceal the knots. The sealant will then show a glossy finish.
  8. Clean tools immediately after use with methanol or Polyprep 771-140 for brushes and rollers.
  9. Apply solvent base coat or GoPrime 190-135.