The primer is the first coat to be applied. The main functions of the primer are to act as a leveler and protector, and to make the base coat easier to apply to the component to which it is applied.
As a leveler: this is important since the cab often has marks and other forms of surface defect after being manufactured in the body shop. A smoother surface is created by leveling out these defects and therefore a better final product.
As a protector: the primer will protect from corrosion, heat differences, bumps, stone-chips, UV-light etc.
Ease of application: by making it easier for paints to stick to the surface a more varied range of paints can be used.
The base coat is applied after the primer coat. This coat contains the visual properties of color and effects, and is usually the one referred to as the paint. Base coat used in the automotive applications is commonly divided into three categories, solid, metallic, pearlescent colors.
The solid paints has no sparkle effects except the color. This is the easiest type of paint to apply, and the most common type of paint for heavy transportation vehicles, construction equipment and aircraft. It is also widely used on cars, trucks, and motorcycles.
The metallic paints contains aluminium flakes to create a sparkling and grainy effect, or as people generally refer as a metallic look. This paint is harder to manage than the solid paints because of the extra dimensions to consider. Metallic and pearl paints must be applied evenly to ensure a consistent looking finish without light and dark spots which are often called "mottling".
Pearlescent Paints contain special iridescent pigments commonly referred to as "pearls". Pearl pigments impart a colored sparkle to the finish which works to create depth of color. Pearlescent paints can be two stage in nature (pearl base color + clear) or 3 stage in nature (basecoat + pearl midcoat + clearcoat)
Usually sprayed on top of a colored basecoat, clearcoat is a glossy and transparent coating that forms the final interface with the environment. For this reason, clearcoat must be durable enough to resist abrasion and chemically stable enough to withstand UV light. Clearcoat can be either solvent or water-borne. One part and two part formulations are often referred to as 1k and 2k respectively.