How to Paint Aluminum Bodywork the Right Way

Today’s vehicles use more aluminum in their bodywork than ever before. And while far fewer classic cars have aluminum bodies, the question nevertheless comes up frequently: how do you paint aluminum? Whether you’re restoring an early Shelby Cobra or simply respraying a workaday vintage Land Rover, it’s a great question. Because aluminum is such a different material than steel, a layer of mystery seems to hover over its repair process. In truth, painting aluminum isn’t vastly different, although there are some special considerations.

Aluminum’s Unique Properties

Refinishing aluminum presents several unique challenges compared to steel. Notably, aluminum naturally forms a thin oxide layer when exposed to air. This can limit the ability of paints and primers to adhere. This layer must be removed through proper cleaning and preparation to ensure reliable bonding.

However, sanding can be more challenging due to aluminum’s softer nature, which can gaul and fill sandpaper. To prevent contamination from other metals, any tools or abrasive surfaces (sandpaper, scuff discs) must be dedicated to aluminum. It can also corrode when exposed to moisture, especially when in contact with dissimilar metals. If moisture gets trapped between the aluminum and paint or filler, it can lead to corrosion and damage.

Aluminum also has a higher coefficient of thermal expansion compared to steel, meaning it expands and contracts more with temperature changes. This can lead to issues such as cracking in the paint or body filler if not accounted for.

Finally, aluminum requires an etching primer (preferably epoxy primer) to bite through any remaining oxide layer. The same goes for body filler if when applying directly to bare aluminum.

Painting Aluminum Bodywork

Preparing and painting aluminum bodywork requires careful steps to ensure proper adhesion and a smooth finish. Here’s a detailed guide:

• Gather Supplies – For tools, an orbital sander, sandpaper (grit 80 to 400), scuff pads, spray gun or paint sprayer, paint mixing cups, masking tape, masking paper, respirator mask, and safety glasses. For materials, an aluminum cleaner/degreaser, etching primer, high-build primer, base coat, clear coat, and paint thinner or reducer.
• Clean the Surface – Use a degreaser or aluminum cleaner to thoroughly clean the surface. Remove any grease, dirt, or contaminants.
• Sand the Aluminum  – Start with 80-grit sandpaper to remove the factory finish and roughen the surface. Sand until the metal is dull. Move to 220-grit, and finish with 400-grit to achieve a smooth surface.

• Remove Dust  – Use a clean cloth or tack cloth to wipe away all dust and debris from sanding.
• Apply Etching Primer  – Use an etching primer specifically approved for aluminum. This promotes better adhesion. Spray or brush the primer evenly and allow it to dry according to the manufacturer’s instructions.
• Sand the Primer – Once the primer is dry, lightly sand it with 400-grit sandpaper to create a smooth surface. Wipe away dust afterward.

• Apply Body Filler or High-Build Primer (optional) – Fill small imperfections such as sanding marks with a high-build polyester primer. If the surface is already smooth, you can skip this step. Conversely, deeper damage such as door dings may require a thin layer of body filler first.

  Most typical polyester body fillers will work fine over epoxy primer for light damage. If the area is deeper, a short-strand glass-reinforced filler will provide better strength. Allow each layer to cure according to product instructions, then sand it down to a smooth finish with 400-grit paper. An aluminum-filled body filler is NOT required., however.

  (Alternatively, you may also apply approved direct-to-metal body filler to clean bare aluminum before primer. The aluminum surface be clean and dry when doing so to prevent trapping moisture. This could cause poor adhesion and the filler could potentially pull away from the repaired area. Modern epoxy primers typically bond better with bare aluminum, forming a corrosion-proof barrier for filler to stick to.)

• Paint Application – When painting aluminum with a base/clear paint system, mix the base coat paint according to the manufacturer’s instructions. Apply several thin coats, allowing adequate drying time between coats. Once the base coat is dry, apply a clear coat for protection and shine. Again, use thin coats for a smoother finish. If you’re using a single-stage paint system, simply apply your color in thin coats and allow to cure. Depending on atmospheric conditions and whether you’re using heay lamps or an oven, curing may take several days. Read the directions on your paint material before you start painting.

• Cut, Buff, and Polish – After curing, you can de-nib any dirt or runs in the paint as you would any other finish. You can also color-sand and polish the clear coat for additional shine using a polishing compound. Carefully remove all masking tape and paper; check for any overspray and clean it up as needed.