Blocking occurs if two painted surfaces stick when pressed together, such as a door sticking to the jamb.

What Causes It?
Blocking can occur when insufficient time is allowed for the paint to dry before closing doors or windows.Using low-quality semi-gloss or gloss paints can also lead to blocking.How to Solve It
Use top-quality semi-gloss or gloss acrylic latex paint. Low-quality latex paints can have poor block resistance, especially in warm, damp conditions. Follow paint label instructions regarding dry times. Acrylic latex paints generally have better early block resistance than vinyl latex paints, or alkyd or oil-based paints; however, alkyds develop superior block resistance over time.

Applying talcum powder can relieve persistent blocking.

Note: Images provided by The Rohm & Hass Paint Quality Institute.