Tendency of a roller to throw off small droplets of paint during application.
Use of exterior paint on an interior surface.
Use of lower grades of latex paints.
Higher quality paints are formulated to minimize spattering. Using high quality rollers that have proper resiliency further reduces pattering. In some cases, a quality wall paint may be preferred for ceiling work, for maximum spatter resistance. Overloading the roller with paint will result in excess spatter, as will overworking the paint once it is applied to a substrate. Working in three-foot square sections, applying the paint in a zigzag "M" or "W" pattern and then filling in the pattern will also lessen the likelihood of spattering.