All you need to know about automotive paint. Ever wondered what makes a great paint job?
Automotive paint
A number of things can make a car special. Performance is certainly one, appearance is another. As far as the latter is concerned, we looked at getting parts chromed a couple of issues ago but the other essential component of a superb looking car is paint.
So, what is paint? This question has a composite answer. The colours we see when we look at a car consist of pigments. These are basically oxides and minerals of various colours that have been ground up into fine powders.
White, for instance, is made of something called titanium dioxide. It can also be made from zinc. Iron oxide can produce reds, and so on for all the others colours available to us today.
Of course powdered pigment won’t stick to a car. It has to be mixed with a liquid that will hold it in suspension both when it’s applied, and after the liquid has dried to form a solid, protective film on the car. Such liquids are called binders and these have other liquids added to them to adjust viscosity.
Local company, Products That Work, manufactures a wide range of two-pack special effects paints sold under the name DNA Genetically Modified Paints. Head Chemist, Roland Harvey, explained the basics of paint for us…
THE GOOD OLD DAYS
In the 1930s and ’40s, cars were painted with alkyd resin enamels that took weeks to dry properly. Lots of experimentation to reduce drying times followed and in the ’50s these paints had evolved into nitrocellulose types that dried in a couple of hours. Still, full curing took time and such paint couldn’t be polished until its internal structure had settled about two weeks after initial application. By the 1970s, these paints had developed into urethane types that used catalysts to harden. These were known as acrylic or urethane enamels.
As plastic became popular in the ‘60s, experimentation with hydrocarbons gave rise to acrylic paint, which has very high concentrations of hydrocarbons in the binders/resins from which they’re made. These paints dry by the evaporation of such hydrocarbons, or Volatile Organic Compounds (VOC).
Locally, acrylics took off on the EH Holden in 1964 and were popular with home painters because they were easy to use. They did, however, require a great deal of polishing to achieve and maintain a strong shine.
By definition the acrylic process has high VOC emissions and this upset the EPA. Further developments to deal with these and other problems led to modern 2K or two-pack paints. These are better as far as the EPA is concerned because they don’t dry by the evaporation of solvents but rather by internal cross-linking of molecules facilitated by the addition of isocyanate hardeners, or catalysts. These catalysts are poisonous.
Paint that doesn’t contain any pigments is the definition of clear and it’s the application of clear coats that creates high gloss finishes. With modern two-pack clears, the layers cross-link very strongly to create extremely stable and hard surfaces. Some can even offer considerable resistance to paint stripper.
PREPARATION THE KEY
There are a number of approaches to painting your car. If the original paint is stable and free of damage you may get away with rubbing it back and applying your new colour over the old for a quick, cheap job. This is far from the best way of doing things but it may suit a really tight budget. Doing so requires a sealer that prevents the new paint from sinking into the old and creating an uneven finish. Sealers (also known as isolators) can also allow certain incompatible paints to be combined, like acrylics and two-packs.
Of course, it’s best to take a car back to bare metal and start from there, which involves panel repair and rust removal. But these are different subjects that we’ll cover another time. Here, we’ll just assume all such work is finished. As such, the first thing applied over bare metal is a rust preventative product like Deoxidine. After it’s rinsed off, primer can be applied.
Primers are really good at sticking to bare metal surfaces. Some have few solids and don’t do much to fill any imperfections. Others have more solids and will fill minor problems like scratches etc. These types are called primer/surfacers. Some primers are self-etching and actually bite into the surface for a very strong bond. Many primers are not water-proof and should be painted soon after they are applied.
Driving around for any time with areas of your car covered in nothing but primer will almost certainly lead to problems after you finally get around to applying your top coat. However, two-part epoxy primers are water-proof. These are a good idea if your top coat isn’t going on for some time.
Spray putties provide the next level of filling after primer/surfacers. Even though they are heavier, they’re still only used to cover minor imperfections. If sanded with a good firm block they will provide a perfect surface for your top coats.
These days, primers come in a range of shades from white, through a selection of greys, to full black. This is necessary because modern OE paints aren’t applied as thickly as they were in years past. Consequently, the primers can often show through and selecting the right one is important for the correct finish. For the same reason, primers are often tinted, too.
TO THE CANDY STORE
So far, we’ve spoken mainly about solid colour base coats. These can be plain but the DNA range, for example, includes extremely bright and vibrant base coats that incorporate special effects. However, most special effects are applied in layers of clear applied over base coats.
Candies are one of the most commonly known. Rather than pigments, which are opaque, candy paints are coloured using dyes, which are partially transparent. So, a candy paint will interact with whatever is underneath it. In fact, when we visited the company’s Scoresby, Melbourne facility, Roland Harvey was in the middle of developing a brand new candy colour, but we’re not allowed to say what it is.
Aside from dyes, clear coats can contain particles that create special effects. The most well known of these would be metal flakes. For those who don’t know, these are small flakes of aluminium that sparkle when they catch the light. In the DNA range they’re called FlakeZ and come in a range of sizes and colours. However, many other things can be added to special effects coats.
If metal flake is the best known effect paint, pearl would have to be the second most popular. Pearls derive their name from the fact that early types were spherical and had the appearance of pearls under a microscope. They are actually made from mica coated with titanium dioxide. Depending on the angle at which light hits a pearl, it will be reflected, absorbed, re-radiated or altered by the layer over the mica, which can be coloured. So, of course, pearls look different from different angles in different light. And these days, the mica flakes are different shapes, which increases the variations.
PTW is constantly coming up with new ideas for the DNA range and has a product called Vari-A-tionZ that changes with light or viewing angle but does so in distinct colour steps. There are also texture effects and others that produce holographic rainbows at various angles and others. The range of colours and effects is very big but the fact that they can all be combined in any way you like creates a huge range of possibilities.
Products that Work runs training courses for both trade painters and civilians to teach them how to use its products and a visit to the website at dna-paints.com will prove instructive. The full range is there and there are also instructional videos showing the processes.
IT’S SHOWTIME!
Trevor Davis has painted more award winning show cars than he (or we) can remember. He explained the basics of painting for us: “Controlling the way the paint is applied to the car is all about the distance of the gun from the work, the speed at which you move the gun, the air pressure atomizing the paint and the volume of paint allowed through the gun.”
Davis said that the closer the gun is to the panel, the more paint will be applied and the faster you’ll have to move it to avoid runs. Pretty logical, really. Turning up the air pressure and/or moving the gun further away calls for slower hand movements. In combination with these factors, the different gun types and nozzles available make for great variation in how paint can be applied. “There’s not really one right way. Different painters achieve quality results in different ways by balancing these factors,” he said.
“It all depends on the application, too. Smash repair is all about matching original factory paint so that the repair is invisible. That’s very different from a show finish which is inevitably much higher quality.”
Interestingly, he said that it’s not possible to achieve the highest quality finish straight off the gun, with no polishing, even using the best products.
“While you might get something that’s acceptable for a concours restored car, you won’t win a show with a gun finish, even with a 2K clear.”
He says standards are so high in top level competition that all cars have to be sanded back and given a machine polish. Some may want to argue the point but you’d be arguing with an embarrassingly large collection of show trophies. Of course, for almost all other applications an off-the-gun finish in 2K clear is perfectly acceptable – it’s designed to be.
Photography: Paul Tuzson