Automotive paint is made up of many compounds, often toxic. The ones of interest to the restorer are the pigment (color), and its delivery medium (the stuff it is dissolved in that allows it to be sprayed from a gun).
All types of paint follow a basic principle – primer is sprayed onto the surface to prepare it for the top (color) coats. The primer provides an even, neutral base for the color coats; color paint does not have good natural adhesion to wood or metal.
One of the oldest types of car paint still available.
Nitrocellulose is based on cellulose, as the name implies, and is an “organic” paint finish. It was used on production cars up until the 1950’s to 1960’s depending on the car manufacturer.
It is not particularly resistant to light or pollution and consequently more modern paints have been developed that last longer. It also takes a long time to dry. Environmental regulations make the purchase and legal use of nitrocellulose increasingly difficult in many countries, due to the amount of organic solvents that evaporate into the air during painting and drying.
Used on many cars from the 1950s to the 1970s, and some, such as Rolls Royce, until the late 1980s. The paint is mixed with paint thinner which evaporates, leaving the paint pigment on the car. The finish is usually deep or glass-like, suiting classic cars. However, the finish must be buffed regularly to maintain it’s look, and is not as long-lasting as 2 Pack.
Acrylic lacquer is the paint of choice for the amateur painter, especially for cars of the period. It has a relatively fast drying time, preventing dirt from sticking to the finish. This is an important consideration for amateurs who usually have less than perfectly clean surroundings to paint in. The fast dying time permits dust or painting mistakes to be sanded down within a relatively short time of paint application.
A cheap type of paint often used on commercial vehicles. The only advantage is low cost, but you get what you pay for; the finish is somewhat dull.
This paint should only be considered for showroom finishes for cars originally painted with it.
Paint used on all modern cars, used increasingly since the 1970s. Very easy and efficient to paint with, requiring less coats than lacquer and drying to a “showroom shine” with no sanding or buffing, in the hands of a skilled painter. The finish looks like plastic, although a skilled painter can reduce this effect. It usually does not look “right” on classic cars.
The finish is also longer-lasting and more damage-resistant. The name comes from the mixture of paint and hardener that dries by chemical reaction, conceptually similar to epoxy glue.
This paint contains isocyanates. If that word looks familiar, think of cyanide. When this paint is being sprayed, the spray can be considered as dangerous as sprayed cyanide gas. In the worst case, death can result from inhalation of 2 Pack paint fumes. In the best case, the immune system is seriously impaired resulting in increased susceptibility to minor diseases and a great magnification of the symptoms.
This paint is not suitable for use by the home painter. Professionals must wear full-body protection with air-fed masks kept at higher than atmospheric pressure to prevent isocyanates from entering the mask. Spraying is done in a filtered spray booth equipped with heating equipment to bake the finish and reduce the drying time.
Most of the paint types above are not compatible, and often different brands of the same type will react. Enamel over lacquer usually does not work, resulting in an unpleasant chemical reaction. Lacquer over 2 Pack usually works, but if there are scratches in the 2 Pack the lacquer will eat into the 2-pack from beneath, via the scratches. Fortunately, the results are immediately obvious. The only solution when this occurs is to strip the surface back to bare metal.
When painting over old paint, always find out the correct type – the paint supplier will be able to help.
Most modern cars are available with pearlescent or metallic paint, although metallic paint has been used on cars including Wolsleys since the 1960s, and pearlescent is a development of the American custom hot rod scene of the 1970s. Both these paint types rely on flakes of material added to colored paint, which is then coated with several layers of clear paint which are buffed to give the final finish. If the flakes were exposed to the elements or buffed, they would degrade or oxidize, ruining the finish. Therefore the “clear over base” method is used.
Metallic paint consists of tiny aluminum flakes, purchased separately from the paint and mixed into it to give the required metallic effect. The effect is controlled by the proportion of flakes used, their size distribution and their reflectiveness, and dozens of types are available.
Pearlescent paint entered the mainstream in the mid-1990s. Most pearlescent finishes consist of a solid base color, a translucent layer of a different color containing mica “pearl” flakes, and clear top coats. Pearlescent paint finishes appear to change color depending on the viewing angle (“color flip”) or the way sunlight strikes them. 1997-spec Minis are available in Amaranth (changes between blue and purple depending on viewing angle, color depth changes under direct sunlight) and volcano orange (changes between lava-orange and bright red). More subtle uses of pearlescent paint change only the shade of the paint.
Metallic and pearlescent paint are the most difficult to apply, and often require large areas to be repainted to cover a small paint repair, so that the seams between the old and new paint are at body panel edges and therefore are invisible. This is necessary because variations in technique and paint color are impossible to reliably duplicate.