Latex paints contain chemicals called plasticizers that allow proper film formation and keep the coating flexible. Many vinyl and plastic weather-stripping materials also contain plasticizers to give them flexibility. When two surfaces containing plasticizers come in contact with each other, they can have the tendency to stick. This condition, known as blocking, will generally occur during the early curing time of the coating, but it can continue for some time. Blocking can also occur on double-hung windows and garage doors. The easiest way to prevent blocking is to use a non-blocking acrylic, or alkyd base paint in areas where it may occur.