Friday, April 23, 2010

Blistering

A series of bubbles in the paint film indicates loss of adhesion to the underlying surface. Most often, moisture is the culprit--it migrates through the back side of the siding (more common with solvent-based paint).

Blistering paint 

Causes:

  • Water or water vapor is pushing the paint off.
  • A solvent-based top coat was applied in direct sunlight to a surface that was already warm, and the paint surface dried before all the solvent was  released.
  • Solvent-based paint was applied over a still damp surface.
  • A freshly painted latex surface was exposed to rain, dew, fog, or other high humidity levels, particularly when the paint preparation was poor.

What to do: 

  • If blisters go down to the bare wood, humidity inside the house is to blame. Locate the source, improve ventilation of moist air, and repair any loose caulking before scraping off blisters, sanding, priming, and repainting.
  • If blisters are only on the surface, scrape them off, feather-sand rough edges of remaining paint, spot prime, and repaint. 

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