Lap marks appear as denser color or an increased gloss where wet and dry layers overlap during paint application. Keeping a “wet edge” is the key to avoiding lapping paint. While painting, you need to move quickly enough so the paint being applied can seamlessly flow in to the just-applied paint.
What Causes Lap Marks?
Lap marks while painting can occur for a variety of reasons, including:
- Letting areas dry before the applying paint to adjacent areas, causing overlapping edges
- Using poor-quality paints
- Painting a porous wall that makes the paint dry too quickly
- Painting in direct sunlight or too much wind
- Not applying the recommended wet film thickness from the paint manufacturer
How to Prevent Lap Marks
Take the following steps to prevent lap marks:
- Paint in manageable area sizes to maintain a “wet edge,” i.e.: Apply paint toward the unpainted area and then back into the just-painted surface. This technique (brushing or rolling from "wet to dry" rather than vice versa) will produce a smooth, uniform appearance.
- Make sure you are using enough paint, especially when using a roller.
- Plan breaks at natural interruptions such as a window, door, or corner. Cut into those areas with a brush while wall paint is still wet.
- Use a top-quality acrylic latex paint, as higher solids in the paint can make lapping less noticeable.
- If the substrate is very porous, apply a primer or sealer to seal the surface and create uniform porosity. This will help prevent paint from drying too quickly.
- Use high-quality painting tools.