Painting explained: adhesion primer, filler, base coat, clear coat

The layers from the bottom up

• Adhesion primer — primer for bonding and corrosion protection; indispensable on bare metal and critical substrates.
• Filler — filling layer that levels fine unevenness and sanding marks in the substrate and is then sanded flat.
• Base coat — the colour-bearing layer. It carries the shade and the effect, but always needs a clear coat as protection.
• Clear coat — transparent top layer. It creates the gloss and, depending on the 1K/2K version, protects the base coat from UV radiation, weather and chemicals.

1K or 2K: the difference

With a physically drying paint, the drying process is based on the evaporation of the solvent. Once it has evaporated the colour pigments remain on the surface; the paint can be re-dissolved with solvents such as acetone or universal thinner.

With a chemically drying paint (2K), drying takes place through a chemical reaction with a second component, the hardener. Once fully cured, these paints are very robust, weather- and UV-resistant, and are not dissolved by fuels or most chemicals.

As soon as the hardener is activated the pot life begins: the window in which the mixed paint remains workable before it starts to cure in the container.

Timings between the layers

To prevent runs from forming, allow a flash-off time of at least 20 minutes between each coat — the waiting time during which the solvent can evaporate out of the freshly applied layer.

At an optimal film thickness the base coat takes approximately 60 minutes to dry, depending on the coat applied and on the object and ambient temperature. If it was applied more thickly, the time increases accordingly. It is best to let it dry overnight before the clear coat follows.

Touch-dry means: the surface of the paint layer has dried, but the coating as a whole has not yet cured all the way through. A paint finish can only take a load once it has cured completely — at least 12 hours, overnight is ideal.

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