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Wax Bleeding on Hardboard Siding

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A light-colored siding surface discolored with dark gray-colored streaks and spots

Painted hardboard can sometimes be discolored by "wax bleed," named for the wax that is used during manufacturing to make hardboard more water-resistant. The wax can migrate to the surface, where it can change the wood's appearance.

What Causes It?
Wax bleeding is most often caused by:

  • Dark paints, which show discoloration more readily than lighter paints due to their tendency
    to absorb heat.
  • Areas without adequate coats, which are more likely to show staining.
  • Paints with low levels of binder, which are more likely to allow wax to migrate from hardboard.
  • Direct sunlight and heat.

How to Solve It
To correct discoloration caused by wax bleeding, it is first necessary to figure out whether wax bleeding is indeed occurring. Do this by:

  • Placing a few drops of household bleach on the discolored area. If no whitening or bleaching occurs, the stain is probably wax.
  • Placing water droplets on both normal and discolored areas. If the water beads up and runs off, it is likely due to wax bleeding.
  • If the surface wax is light, use a detergent solution to clean any discolored areas. With severe cases of wax bleeding, clean the surface completely by wiping it with a solvent such as mineral spirits. Change your rags frequently as you clean, and allow the surface to dry thoroughly before painting.

Note: Images provided by The Rohm & Hass Paint Quality Institute.

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