Why is my wet paint bubbling?

Paint bubbles develop when the temperature of the painted item rises suddenly, such as when direct sunlight hits the area, according to BobVila. The blisters occur most often with oil-based paint that is applied in multiple coats, with the top coat trapping the wetness of the bottom layer.

The bottom coat of paint produces a vapor that expands when the painted area gets hot, causing bubbles in the top coat. Blisters can be scraped off, and the painted surface can then be smoothed and repainted away from full-sun exposure. Light-colored paints and thin coats usually produce fewer bubbles than dark colors that are applied thickly.