(cloned from the old mini.org web site – original author unknown)
Paintwork is a restoration task that is often, like the engine build, left to professionals. Professional car painters have more and better equipment at their disposal, along with a large amount of experience and training. However, unless you pay top prices, you cannot guarantee that they are going to take more care of your car than they do of the usual insurance repairs and to-a-price resprays that make up most of their work.
It is possible for the home restorer to achieve results as good as a professional, though it may take ten times as many hours and a lot of mistakes. However, if you paint a car yourself, you know for sure that those rusty patches have been adequately repaired, and no rust, water or dirt is trapped in any crevices waiting to rot out your panels within a couple of years.
Choosing a Paint Shop
Most people are happy to leave car painting to professionals with their superior training and resources. Care is needed when choosing a paint shop for your car, to ensure that they work to high standards, as problems with poor preparation and shoddy technique may not become visible for up to two years after the paint was applied.
When obtaining quotes, be specific about the work you want done. For example, you may wish to have the entire body shell stripped, all dents and surface imperfections removed, the car painted with two-pack paint, and the box sections treated with rust proofing chemicals. If you ask only for a quote to paint the car, painters will tend to quote for a respray of the outside of the shell with minimal surface preparation, as this is all that most people are prepared to pay for. Get an itemized quote if possible.
Do not be surprised to get quotes ranging from a few hundred dollars/pounds/etc to several thousand. You get what you pay for; the more expensive quotes will include much more labor in surface preparation, which cannot be skimped on if good quality results are desired.
Inspect the premises where the painting is to take place. The paint shop should be clean, well-lit and contain a spray booth. Tools should be neatly stored, clean, and in good condition. Staff should be wearing appropriate protective clothing, and should not be painting outdoors or in the same room as general preparation work is done, or sand and dirt will accumulate in the wet paint. The use of newspaper for masking is a sign of unprofessionalism.
Paint shops meeting the above conditions will give the highest quotes and the best quality work. Beware of any paint shop that tries to prevent you from speaking to past customers or inspecting any of their finished work.
The process of writing a quote should take more than just a few minutes and should involve a thorough assessment of the car. For this reason, paint shop owners may be wary of writing quotes for potential timewasters.
Restoration shops are less likely to have spray booths, and the best restoration shops will have their own fully equipped paint shop, or farm painting out to someone better equipped. Restoration shops that paint cars in their workrooms or even "out the back" may still give excellent results, but they have to work much harder under those conditions to get them.
Finally, contact local car clubs and get in touch with the owners of concourse competition-winning cars. Ask them where they had their cars painted. This should provide you with a few leads.
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.
Paint is available in many different types - choosing the type of paint to use is very important. Application techniques, cost and the resulting appearance vary widely between them. The major different paint types are summarized below, in approximately the order they were introduced:
Nitrocellulose One of the oldest types of car paint still available.
Lacquer 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.
Acrylic Lacquer 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.
Acrylic Enamel 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.
2 Pack 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.
Metallic and Pearlescent Paint
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.
With practice, and preferably some training, a DIY painter can master metallic and pearlescent painting to give acceptable results. Fortunately, however, most classic cars are painted in solid colors.
DIY Car Painting
An investment in tools and training is needed if you choose to paint your car yourself. In car painting, as in other car restoration tasks, there is no better teacher than experience. Excellent textbooks are available and should be available in the local library, but nothing compares to seeing other people's technique in action. If there are no night courses in painting near you, find a local restorer or painter who is willing to teach you. Failing that, the local paint store may have tutorial videos, as these are distributed free as promotional material by the competing paint companies.
The basic tools needed for painting are:
· An air compressor of at least 2 horsepower. This must be equipped with an oil and water trap, or these impurities will damage the paint finish. An air compressor can also be used to power air tools which are often superior and cheaper to their electrical equivalents.
· A spray gun. The cheapest spray guns that give acceptable results cost around $US100, the best cost $US500 or more. This translates to an improved "off the gun" finish requiring less flatting down. A spray gun is essentially an SU carburetor for paint, with a needle and jet to control the amount of paint delivered. Discuss the type of paint you will be using with the vendor; they will be able to provide the correct needle/jet setup for the brand of paint. Cheap guns will only have one setup available.
· Other tools such as a grinder and buffing wheel can save hours of work smoothing and buffing the finish, as well as having other uses, but hard manual labor with sandpaper and cutting compound can achieve the same results.
A room to paint in is also necessary. Acceptable results may be obtained outside if the air is still and shady, the temperature is even between 2225 degrees Celsius, and there are few insects, deciduous trees or dusty areas nearby that are likely to contaminate the paint. In practice, the best one can hope for is to have a few contaminants that need to be sanded out and the surrounding areas repainted. To improve the chances of success, the ground and buildings around the car can be damped down with a hose to prevent dust from blowing around.
If painting inside, the room must be much cleaner than the average workshop or garage. Years of accumulated dust in the rafters and floors of a typical garage will be blown down onto your paint by the action of the spray gun stirring up the air. Roofing felt can be used to line the floor; when wetted slightly it will trap dust and dirt very effectively. Line the walls and ceiling with plastic if possible, but provide for ventilation while painting or the concentration of fumes will soon rise to a dangerous level.
Acrylic lacquer or nitrocellulose should be used by DIY painters (unless an enamel finish is required). The fast drying time minimizes the amount of dirt that can stick to the paint while it is wet, and allows for defects to be sanded out shortly after the paint has been sprayed.
Health and Safety
You will encounter dozens of toxic chemicals while painting. These include organic solvents (if you can smell them, they are dissolving your brain cells), cyanide, heavy metals such as zinc, mercury, and lead, and other toxic elements such as chromium. Symptoms of exposure to these chemicals can be some of: temporary lightheadedness, temporary and permanent immune system damage, damage to the central and peripheral nervous systems, brain damage, eye irritation or blindness, birth defects, muscle tremors, cancer, and death. Some of these symptoms can develop after brief exposure, especially to two-pack paint, of seconds or minutes in some individuals. Lacquer paint is far less dangerous than two-pack, but most people could expect to develop some sort of illness after painting a car without protective equipment.
Always follow the manufacture’s safety instructions for products you are using. For home use, eye goggles, chemical-resistant gloves and a dual filter air mask (carbon filter plus gauze filter), plus overalls, suffice for lacquer or enamel painting. Disposable masks are not up to the task. All this safety equipment should be available at the shop you buy your paint from.
If applying two-pack paint you will need to rent a spraybooth and take some training in safety precautions. In some countries, two-pack paint is freely available, but in others, it is restricted to those with the right qualifications and equipment. This is for a good reason. The safety equipment includes full-body protection, as isocyanates can be absorbed through the skin and eyes. A positive-pressure air-fed mask is used. This mask is fed from the air compressor and the air inside is therefore at a higher pressure than the air in the booth, preventing the isocynates from making their way into the mask.
Most restorers wish to repaint their projects in the original colors, or at least in a color that was available for their model. Paint codes and mixing instructions for most British cars are available from British Motor Heritage in the UK. Many American and Japanese cars have their paint codes stamped on their chassis ID plates. Any paint shop can mix the right color based on this information, although it is unlikely to match the weathered original paint on the car.
Owners of most classic British cars can also obtain a Heritage Certificate from British Motor Heritage that will show the original paint color/s for their car along with details of the original specification.
If no information on the paint color is available, the paint shop can mix paint to match that already on the car. The best places to match to are areas that received little wear and exposure to sunlight, such as behind the dashboard or underneath trim.
A Typical Paint Job
A typical restoration-type respray might include the following steps, using acrylic lacquer paint.
1. Paint stripping.
2. Metal conditioning. Exposed metal is rubbed down with a metal conditioning product which consists mostly of phosphoric acid. An iron phosphate coating is formed which resists rust and provides an excellent surface for the adhesion of paint.
3. Etch priming. A light coat of etch primer is applied. This usually translucent yellow-green and should not be applied thickly. Etch primer provides a good base for the rest of the paint coats. It is not necessary, but is strongly recommended.
4. Priming. Approximately four coats of primer are applied and the paint is left to dry at least overnight but preferably for at least a week.
5. Rubbing down. A fine mist of colored paint is sprayed over the primer. The surface is then sanded back with 600-grit sandpaper. When all the color is gone, the paint is rubbed down. If any patches of color remain, they reveal dents that should be filled in or hammered out.
6. Top coat. Four to six top (color) coats are applied, giving at least enough time for each successive coat to be dry to the touch. (Any more coats and the paint will be too thick, risking cracking. Anyone who boasts of the 20 coats of paint on their car is mistaken in thinking this improves the finish quality). For metallic or pearlescent paints, 4 color coats might be followed by 3 to 5 coats of clear paint.
7. Rubbing down. The top coat is rubbed down with 1200 grit sandpaper until it loses all its gloss.
8. Buffing. A wool buffing pad is used with buffing compound to bring the surface to a mirror finish. This can be accomplished by hand but takes much time longer. Care is taken not to eat through the paint at the edges of panels.