Car paint, types, operation, advantages and disadvantages

The finishing touch

By: Dolf Peeters

Car paints have been around as long as there are cars. Only the way they are made - and applied - has changed just as much over the years as the cars themselves. We look back on 120 years of car paint history and see what we can do with that now.

De paint op cars has two reasons for existence. It is important for its appearance and it must protect the car against the elements. The first cars were painted in the same way as coaches. The painters applied the paint with brushes in several layers. For that, the bodywork - the bodywork - had to be carefully put in the primer and varnished. From the beginning to the gleaming end result it could have been just eight weeks.

This traditional approach did not fit in with the mass production that was starting. In Germany, car manufacturers made passenger cars in 1901 845. Nine years later there were 12.000.

The paint process had to be able to keep up with that production. The oil-based lacquers were improved and the drying times were shortened by increasing the temperature. But in 1910, car paint was not dry until after three weeks. The end of vegetable oil-based paints came with the birth of Ford's Model T. Ford wanted to turn it into 1.000 every day. That was no problem thanks to the production line. But with an 20 day drying time of the paint, he would need a conveyor belt of 100 kilometer length.

Ford therefore sought an alternative that allowed a drying time of up to 50 hours. He ended up in Japan where shellac was used. The new paint was considerably thinner and could therefore be processed with the spray guns invented in 1910, Detroit. The biggest advantage: the thinner coatings dried faster. In the required quantities, this well-known product was only available in the color black, also as 'Japanese lacquer'. That is why the T Ford, as Henry Ford put it, was "available in all colors as long as it was black".

After the first world war, technology went ahead with leaps and bounds. The arms industry had made huge quantities of nitro cellulose powder worldwide. The idea was to do something peaceful with it in one way or another. One of the results from that revenue-oriented thinking was the cellulose lacquer. There were few solids in the product and it had little gloss. That is why it had to be applied in several thin layers. Then it had to be polished - polished - to shine. Brushing was still a lot of work, but it already saved considerable time and there was more choice in colors from that moment on. Until 1930, cellulose lacquer was the norm for all car manufacturers.

But already in the thirties, chemists were working on the development of synthetic resin varnishes. Fatty acids had become available in large quantities as a by-product of the explosive growth in the oil industry. They were boiled with alcohol and so came into being. Such as synthetic resin lacquer. In this way, varnishes could be made that could be set up in thicker layers per spraying session, dried faster and already had a nice shine without much cleaning. At the same time, the development of more and better color pigments came in and accelerated. The use of titanium oxide made it possible for the first time to produce very bright colors including clear white.

It was also the birth time of the 'effect lacquers\ '. First, ground fish scales were mixed by varnish for that unique color experience. What is now 'silver metallic' was first called 'fish silver paint'.

In the time that followed, the cellulose nitrate coatings and synthetic resin coatings were constantly improved. The admixture of resins, oils, plasticizers and the like with the nitro lacquer resulted in the nitro combi lacquers with more gloss and better polishability. The end station in this development was a product that only had the basic properties of the nitro lacquer: the thermoplastic acrylic lacquer. After application, the paint layer was exposed to heat and melted one more time. In addition, the paint settled so smoothly that police were no longer needed. In Europe, for example, Ferrari and Opel started coloring their products in this way. In the States GM went thermoplastic.

But most cars left the assembly line in a further developed synthetic resin lacquer. The addition of melamine resins thereby increased hardness and gloss and improved the service life of the paint layer. The end point in this evolutionary trajectory is the two-component synthetic resin lacquers, which are usual up to the previous eighty, whereby the profit lies mainly in processing. In the 1990s, the water-based paints started their rise. Water takes over there in the function of the solvent and the development was controlled for environmental reasons. There was only an ever smaller fraction of diluents and solvents from the petroleum range. The actual breakthrough of the water-based varnishes was based on the law. Since January 2007, the share of solvents per liter of base coat may not exceed 420 grams. Most manufacturers are now around the 100 gram. The keyword in that story is 'base lacquer'. The transparent or cover layer with which the water-based varnish must be 'sealed' is, as usual, a solvent-containing acrylic varnish. And that is precisely why the water-based varnish in terms of hardness, gloss and ease of brushing cannot match the old faithful synthetic two-component (2K) varnish.

This has brought us right into our current classic world. Because acrylic lacquers are still available without any problems. Even despite the fact that they are almost no longer used as a base coat for new cars. But even if a delivery problem for acrylic lacquer should arise in the future, we do not have to worry about it. The properties of 2K and water-based paints do not differ much. They do not bite each other, and that is important in the (partial) restoration of a classic. That 'biting' is a point when the original lacquer layer is a cellulose nitro lacquer as it was often used in England in the fifties or if there is a show-shine & sale spray job from the States. Dynamic sales overblowing with a more modern paintwork can have a dramatic effect on an old 'thermal' paintwork of a GM mastodon. Then there is only one solution: balding down to the bare plate.

But how can you determine what kind of lacquer layer there is on a classic? The simplest test is best: rub it briefly with a cloth dampened with nitrobenzene (industrial thinner). A cellulose nitrate lacquer then colors the cloth immediately and clearly and it becomes sticky. Thermoplastic acrylic lacquer reacts the same. And to definitively determine which of the two types is involved, you have to let a sanding disc smell the paint. Cellulose lacquer then disappears into a cloud of dust, TPA (thermoplastic acrylic lacquer) melts and allows the sanding disc to 'fill up'. That TPA can even soften due to the heat of the sun or (the hood) engine heat. That is why it can never be repainted carefree with a 2K paint (which often happens with USA 'sales spraying'). 'Isolating' the old paint layer with a special primer is fine. But costs extra.

Waterborne paint can also not just get an 2K jacket. The tensions between the different layers of paint will lead to wrinkles, cracks and scars. And then again applies: back to the end. Down to the bare metal. The cellulose nitro lacquer is in that context forgiving: It can never hurt to first put an epoxy primer over it, but the lacquer is well compatible with modern lacquers. The synthetic resin varnishes that were used until the 1980s are much harder to recognize. After removing the cloth soaked in nitro benzene - think about the gloves! - the paint becomes temporarily soft and dull. If the paint reacts like this, it is not possible to spray it with a modern water paint. It takes years and years before the solvents from a synthetic resin lacquer have disappeared and it is 'inert' (dead). Here too, the possibility of insulating the layer with an epoxy spray is an alternative to completely removing the old lacquer layer. Acrylic lacquer is normally easy to recognize. The rag with nitro toluene or benzene or industrial thinner has no grip on it. The same goes for modern water-based paints. And combining solvent-based paints with water-based paints is also no problem.

When we talk about the restoration of vehicles from the first half of the 'twenties', it can usually still be done with the original paints. The availability of the 'binder' for cellulose lacquers is now a problem. Master sprayer Theo Terwel from Vorden has searched all the way to China. But nothing found.