Having paint on everything; unexpected reactions from paint to paint

Often people write 'someone' when they are actually talking about themselves. And people who don't care about anything 'don't care about everything'. However, this text is about someone else who didn't care about everything, but that was only the beginning of the misery.

Because immediately after spraying, he discovered that his improvised spray booth (building foil) had not been close enough so that spray mist was deposited everywhere. And the next day he discovered that his newly sprayed paint had started to react with the old paint layer. That is why we go through the paint world with a few clear steps.

Paint types

Before spraying it is necessary to know what type of paint the car - or let it be the motorcycle - is sprayed with. Over the decades, various paint systems have been used in factory paintwork. The list below provides a nice guideline in that process.

NC varnish (nitrocombination varnish)

In the case of these nitro or nitrocombination lacquers, curing takes place through the evaporation of the solvents and diluents. The drying time is therefore simply a physical phenomenon. Nitrocombination lacquers have alkyd resins as added binders to improve gloss and weather resistance. The dried lacquer layer can be dissolved again with a sharp solvent.

KH lacquer (synthetic resin lacquer with alkyd / melamine resins

Depending on the composition, this lacquer dries at normal room temperature, but is also supplied as a stoving lacquer. During oxidative drying, oxygen is absorbed from the air, resulting in a chemical change in the binder. As a result, the lacquer layer is no longer soluble. This lacquer can easily be used as an undercoat for another lacquer system.

TPA (thermoplastic acrylic lacquer)

This type of varnish has, by hardener, addition drying, i.e. chemically reacting, binders and a high filling capacity. This type of varnish is partially sensitive to solvents and can therefore cause adhesion problems.

TSA (acrylic / muffle lacquer thermosetting)

Just like TPA, but if properly cured it can be maintained as an underlay with impunity.

Determine the paint type

This is best done with the dissolution test. Rub a white cloth soaked in nitro (thinner) over the paint in a place that does not stand out. If the cloth discolors, it is because the paint dissolves. This is then a nitro / or thermoplastic lacquer layer.

During sanding you can feel whether the coating has hardened. If the lacquer does not give off dry dusty when sanding but feels 'tough', then it is not suitable for applying a subsequent layer of lacquer. It is best to remove it completely. Or you can draw a chance: Put the paint in a few thin, layers of mild, well-curing primer. The solvents in that primer must be able to evaporate quickly (temperature!) To prevent the underlying paint from dissolving. It serves as a neutral separator between the old and the new coating.

Metallic paint: One or two coats?

It is not easy for most DIYers to see by eye what kind of metallic paint has been used: A two-layer or a single-layer system. With a piece of fine sandpaper or a pocket knife you can determine what you are dealing with. If you see a colorless to milky scrape, the metallic paint has been covered with a clear coat.

The clear coat over the metallic layer gives more color and depth to the base layer than can be achieved with a single system.

Interesting material, that lacquers and spraying. We will come back to it again!