Classification and Types of Paints

The paint manufacturing industry produces a variety of products. These products are used to protect, preserve and beautify the objects to which they are applied. In general, paints are classified by their proposed function or service applications such as architectural coatings, industrial coatings, special purpose coatings, varnishes, lacquers, etc. The characteristics of most important classes are summarized below. 

Architectural coatings (house paints). This class includes paints and coatings, which are used for the decoration and protection of exterior and interior of buildings. They are divided into (a) solvent-based and (b) water-based paints. The normal materials used in the painting of buildings include primers, undercoats, and finish coats (top coats). In the year 2003 in the United States, the architectural paints were about 40 percent of the value of all paints. 

Primers are pigmented coatings that are applied to new surfaces or to old cleaned surfaces, prior to the application of undercoats or top coats. Its main functions are to achieve adequate adhesion to the substrate and to provide good intercoat adhesion for subsequent coats. They are specifically formulated for particular substrates such as wood, metals, concrete, and other masonry surfaces. Concrete and other masonry surfaces are alkaline and often require special surface treatments. For etching and neutralization of these alkaline surfaces, hydrochloric or phosphoric acid washing is usually done. 

The undercoats are pigmented paints that are applied to primed surfaces prior to the application of finished coats. The undercoats are high pigment paints with a matte finish and a color to complement that of the ultimate finishing coats. 

The finish coat or the top coat are the final coats for use both over primers or undercoats, and directly on a substrate. They are formulated to provide good adherence to the undercoat, high durability, the desired appearance, and other properties. These properties are invariably controlled by the class of resin used as the principal binder in the top coat. The nature of these various binders is discussed earlier in Sec. 7.2. In this section, the formulation and manufacture of some exterior and interior house paints are discussed. 

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