What is it?
These bubble-like appearances are caused by blistering, which happens when certain areas lose adhesion, forcing the paint film to lift from the surface.
Possible Causes:
• Due to trapped moisture or gases in paint film (more likely in enamels)
• Painting under direct sunlight or on surfaces that are too warm. This is especially true if the coating you’re using is dark in colour and solvent-based.
• Applying an oil-based finish on a wet or moist surface.
• Exposing water-based finishes to dew, high humidity or rain immediately after the paint has dried. This becomes a greater issue if the surface has not been properly prepared at first, or if the quality of paint is poor.
Solutions:
• Scrape and sand blisters till they go away and then repaint it.
• Remove sources of moisture. Repair loose caulk and install vents and exhaust fans wherever possible.
• Prime and paint the wall with a high quality water-based exterior paint.