Tech Questions - Preparation of Aluminum Surfaces


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How do I prepare my new aluminum surface for painting?

Aluminum surfaces that have never been painted require special preparation. New aluminum has a thin layer of pure aluminum coating the top surface. This alclad surface is not favorable to adhesion of primers. The surface of new aluminum must be roughened to accept primer. This is accomplished using a conversion coating.

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What are the steps for applying conversion coating to new aluminum?

First of all, wash the part thoroughly using 310 alkaline cleaner. Then use E-2300 Conversion Coating, dilute according to the directions, and apply using a brush or a sponge. Keep the surface wet for at least 5-7 minutes. Then rinse completely with clean water. Do not allow the coating to dry on the surface.

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Should I take any precautions with these chemcials?

When using conversion coating always protect your eyes and your hands. An eye shield is best to use.

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What about repainting old aluminum surfaces?

After stripping off the old paint the surface must then be cleaned and properly prepared. Remove any corrosion using fine sandpaper or Scotch Brite pads. Old aluminum must be acid etched before being treated with conversion coating. Use E-2310 Acid Etch. Dilute it with two parts of water and apply it using an ultra-fine Scotch Brite pad. Rinse it thoroughly with clean water. Then apply the E-2300 as discussed for new aluminum.

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Should I always prime an aluminum surface before painting?

Absolutely. You must prime aluminum surfaces prior to painting. Use only an epoxy primer (EP-420). Epoxy primer will provide corrosion protection and also provide a bonding surface for the topcoat paint.

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What if the part has zinc chromate on it. Do I need to remove that prior to spraying on the epoxy primer?

Usually you can sand the surface completely and then spray epoxy primer over the zinc chromate. Occasionally epoxy primer will lift old zinc chromate. If that is the case you should strip it off.

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What color primer should I use?

That is up to you. White and green are available. If you are painting a light color as the final topcoat you will probably want to use the white primer.

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Can I brush the primer on the aluminum surface?

Brushing it on will provide corrosion protection for the metal but you will not be able to get a smooth, glossy surface with the final topcoat. You should spray the primer on aluminum surfaces that will receive topcoat paint.

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