CAUSES: Wet and dry layers overlapping. Failure to maintain a wet edge during painting. Painting too large an area at one time. Unprimed porous surfaces. Painting when temperatures are above 90 degrees F. Inadequate stirring and over thinking.
SOLUTIONS: Another finish coat usually will hide lap marks. Proper priming will help avoiding lapping on new work. Always paint from wet to dry and in small sections to keep a wet edge. Plan natural breaks like doors, windows and corners. Temperatures under 90 degrees F.