The binder is one of the most important ingredients in modern paints. Although linseed oil and other organic binders such as egg tempera were once commonly used by painters to lock the pigment into place on surfaces, today’s binders are formulated for quick dry times and superior tenacity.
Oil-based binders are the oldest type of coating material used in paint. Although linseed oil and tung oil are serviceable, they do have long drying times, and can be quite vulnerable to chipping or cracking once dry. In modern commercial painting, polyester compounds called alkyds are introduced in the oil medium in order to speed drying time. The drying time is dependant on the ratio of alkyds to oil.
Latex-based binders are a dispersion of microscopic plastic particles in water. Although called latex, this type of binder has nothing to do with latex rubber. It gets its name from the similarity of the milky-white liquid suspension to the natural sap of the rubber tree.
Currently, three types of latex-based binders are in common use: acrylic, vinyl acrylic and styrenated acrylic. 100 percent acrylic paints are used as top of the line exterior paints because of their excellent resistance to cracking and peeling. Inside, they offer superior mold protection and are resistant to alkali-based chemicals found in many cleaning products. Vinyl acrylic paints and styrenated acrylic are often used when cost is a factor, although styrenated acrylics find use as metal surface coatings and masonry sealers.