Home Problems & Solutions Formation of bubbles during application causes the appearance of cratering on the topcoat. Exterior Wall Painting • Interior Wall Painting CausesNot using the right roller.Applying several coats without allowing the previous coat to dry.Applying paint on a very porous surface without priming.Excessive stirring of the paint before application. SolutionRemove the problematic surface.Apply a suitable product. TIP: For water-based ecological enamel paints, do not use foam rollers. TIP: Avoid intense stirring before application.