Blocking occurs when two freshly painted surfaces stick together when pressed against each other, such as a door sticking to the jamb or window sticking to the sill. Frequently, when one surface "breaks" free, it leaves paint from its own surface or peels paint from the opposing surface.
Pressing newly painted surfaces together before they have fully dried.
Using slow-drying, oil-based paints that have been stored for long periods.
Applying another coat of paint before th first coat is completely dry.
Applying excessive amounts of paint on a surface, causing extended drying times.
Using a low-quality, water-based semi-gloss or gloss not designed to have block resistance.
If the area has never been painted, prime the surface with a high-quality primer.
If blocking condition already exists, scrape or sand the surface to remove all loose paint. Clean off any dust or dirt and then prime the area with a high-quality primer.
Doors and windows should be properly adjusted for free and smooth operation prior to painting the surface.
Use a top quality semi-gloss or gloss acrylic latex paint. Low-quality latex paints generally have poor block resistance than vinyl acrylic paints or alkyd and oil-based coatings. Alkyds, however, can develop superior block resistance as the film hardens,