Lapping

Lap marks appear as denser areas of colour, or increased gloss, where wet layers of paint have overlapped with dry layers during painting.

POSSIBLE CAUSES

Failing to maintain a wet edge when painting.
Using a low-solids, economy paint.

SOLUTION
Maintain a wet edge by applying paint towards an unpainted area and then back onto a freshly painted section. Work quickly to ensure that you’re always lapping a new layer of paint onto paint that is still wet. This technique (brushing or rolling from wet to dry, rather than vice versa) will produce a smooth and uniform appearance. Keep the area you are working on to a manageable size, and plan for interruptions at a natural break, such as at a window, door or corner.

Always use a top-quality acrylic water-based paint. The higher solids (pigments and binder) content of this paint makes lapped areas less noticeable. If the substrate is very porous, it may need a primer or sealer to prevent the paint from drying too quickly and reducing wet edge time. Solvent-based paints generally have superior wet edge properties.