Foaming and cratering frequently occur when bubbles (foaming) form. When the bubbles break during application and drying, they result in small, round concave depressions (cratering).

What Causes It?
A variety of problems during paint application can cause foaming and cratering.

• Shaking a partially filled can of paint.
• Using low-quality paint or very old latex paint.
• Applying (especially rolling) paint too rapidly.
• Using a roller cover with the wrong nap length.
• Excessively rolling or brushing the paint.
• Applying a gloss or semi-gloss paint over
  a painted surface.

How to Solve It
All paints will foam to some degree during application, but higher-quality paints are formulated so the bubbles break while the paint is still wet, allowing for good flow and appearance.

Avoid excessive rolling or brushing of the paint or using paint that is more than a year old. Apply gloss and semi-gloss paints with a short nap roller, and apply an appropriate sealer or primer before using such paint over a porous surface.

Problem areas should be sanded before repainting.

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