Close up image of a surface that look like the staining substance has bled through the paint film.

Wax Bleed - EXTERIOR

Stains that come from waxy substances in the reconstituted wood products used to make hardboard siding. When the substrate is painted, these staining substances bleed through the paint; they can even bleed through some primers, possibly causing dirt pickup, mildew and/or poor paint adhesion.

Causes

  • Failure to apply a proper primer to hardboard before applying the topcoat.
  • Allowing hardboard siding to weather before being painted.
  • Use of dark paint colors, which absorb heat and can accelerate wax bleed.
  • Too little paint; wax bleeding is more likely with thin paint films.
  • Applying a hard finish over a softer coat without priming, or painting over a glossy surface without sanding.
  • Using low-quality paints with lower resin content that allows wax to bleed through the paint film.

Solutions

  • Unprimed hardboard should be primed or painted within 30 days. Factory-primed hardboard should be painted within 90 days of installation. Apply the recommended primer and two topcoats on unprimed hardboards.
  • If wax bleed is observed, first determine if wax bleeding is the problem:
    • Place a few drops of bleach on the discolored area. Household bleach does not affect wax so if there is no whitening or bleaching, the stain is likely to wax.
    • Place a few drops of water on both normal and discolored areas. If the water beads up and runs off, a wax film probably exists.
  • If the wax is light or moderate, the area can be cleaned with a detergent solution. In cases of severe bleeding, the surface must be cleaned thoroughly with mineral spirits. Dispose of all waste materials in accordance with local regulations.
  • Allow the surface to dry thoroughly before priming. Prime the surface with a high-quality primer and finish with high-quality exterior paint.

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