Lap marks are those ugly stripes caused by uneven layers of paint buildup. They occur when you roll over paint that’s already partly dry. (In warm, dry conditions, latex paint can begin to stiffen in less than a minute!) The key to avoiding lap marks when doing DIY wall painting is to maintain a “wet edge,” so each stroke of your roller overlaps the previous stroke before the paint can begin to dry.
To win work, contractors generally have to bid against other suppliers. To make an accurate bid, they estimate the time and materials required to complete the job. They measure the area to be painted and discuss the type of finish the customer requires. They assess the quality of the surfaces to work out how much remedial work they must carry out before painting. They might have to remove old paint or wall coverings, or repair cracks and other damage. They also calculate the cost of any essential equipment, such as scaffolding for exterior walls.