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Diecast painting

RELATED TOPICS: PAINT
Q: I recently stripped a diecast model and repainted it with Tamiya acrylic - which, over a relatively short period of time, has begun to lift off in spots. I washed the stripped surface and allowed it to dry thoroughly before painting, and I was careful not to handle the car with greasy fingers. What happened?

- Bob Scott
Central Falls, Rhode Island

Ken: Well, Bob, it sounds like you've just discovered the inherent difference between styrene and diecast metal. Actually, diecasts are typically more of an alloy than a single metal.

By definition, an alloy is "a substance that is a mixture of two or more metals" or it can be "a less-valuable metal mixed with a more-valuable one, often to give hardness."

Diecast models usually contain a high quantity of zinc, which will start to oxidize immediately when exposed to air. Oxidation means rust, and rust means trouble. Even the smallest presence of oxidation will cause paint (and some primers) to adhere poorly, resulting in the problems you're facing.

What to do? Deal with the problem as if you were painting a full-scale metal vehicle. Use an etching primer that will prep the metal (alloy) and prevent the surface from oxidizing before you paint. You can use automotive etching primer or the Tamiya brand of prep - called, logically, "Metal Primer." After you've sealed the bare metal (alloy) surface, add primer and paint the way you would on any other model, and the problem should disappear.

Just remember, different materials require different prep.


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