Resinous exudation on soft wood knots

 

Resinous exudation on soft wood knots

Causes

  1. Knots and sap veins in several soft woods such as pine, spruce and fir exude resin under heat or sun. Resin oozes through the coating giving it a yellowish colouration after a few months.

Solutions

  1. None. Resinous exudation cannot be stopped. It only ceases when there is no more spew in the knots. To remove resin, heat knots and scrape excess resin. Remove afterwards all residues with alcohol, turpentine or Polyprep 875-104.
  2. Resinous exudation is not the same as bleeding. It occurs mainly on wood containing tannic acid and resin (pine, spruce and fir). The solvents in coatings dissolve tannic acid and resin. During the drying process, solvents evaporate through the paint film giving a brownish colouration to coatings.
  3. Darker shades promote resinous exudation.