Roller marks or "stipple" is an unintentional textured pattern left in the paint by the roller.
What Causes It?
Roller marks can result if the paint is applied using an incorrect or low-quality roller cover. Using an incorrect technique can also lead to this condition.
Finally, lower grades of paint are more prone to having roller marks appear.
How to Solve It
When applying paint, make sure you use the proper roller cover. Avoid too long a nap for the paint and substrate. Use quality rollers to ensure adequate film thickness and uniformity.
High-quality paints tend to roll on more evenly due to their higher solids' content and leveling properties.
Pre-dampen roller covers used with latex paint and shake out any excess water. Begin rolling at a corner near the ceiling and work down the wall in three-foot-square sections. Spread the paint in a zigzag "M" or "W" pattern, beginning with an upward stroke to minimize spatter. Then, without lifting the roller from the surface, fill in the zigzag pattern with even, parallel strokes.
Do not let paint build up at roller ends.
Note: Images provided by The Rohm & Hass Paint Quality Institute.