The Problem: The appearance of a denser color or higher gloss where wet and dry layers overlap.
Causes: Can include failing to maintain a “wet edge” when applying paint, or not priming a porous surface.
How-to-fix: When applying paint, maintain a wet edge by starting from the unpainted area and going back into the just painted area. Brushing/rolling from dry to wet will help produce a smooth uniform appearance once the paint has dried. It’s also wise to work in manageable sized areas. You typically want to finish rolling out a wall or ceiling before taking a break. This rule is especially important when applying stain to bare wood. If the substrate you’re painting is very porous, a primer/sealer should be applied to help prevent the topcoat from drying too quickly.