Since aluminum is non-porous, panting it can be hard. That’s because paints don’t stick well over non-porous materials. So, how can you paint it?
To paint aluminum, sand the surface, apply self-etching primer, and then apply the paint. Sanding will create tiny ridges (pores) on the surface, and self-etching primer will etch and stick over the aluminum. This allows the paint to stick better.
If you don’t sand or primer, the paint will have a weak bonding with the surface and will get removed from minimal contact.
Things To Know
You must sand and prime the aluminum surface to create ridges (pores) for the stick to soak into. The slick and non-porous surface of aluminum prevents paints from penetrating its surface, meaning paint won’t stick.
Sanding will abrade the surface (create holes) so it becomes textured. Since the surface becomes textured and not slick, paint can penetrate it (a bit) and stick. To improve the adhesion quality, you must also apply a coat of self-etching primer.
The self-etching primer contains phosphoric acid ester, meaning it etches the surface and sticks over aluminum while other primers can’t. The primer will create a textured layer into which the paint can penetrate and stick.
Types of Paints To Use:
The best paint to use on aluminum surfaces is latex or acrylic paint. These water-based paints dry fast and don’t highlight scratches or imperfections on the surface.
You can also use oil-based paints, but their glossy finish will highlight stains and imperfections. So, you must either remove the imperfections by sanding or apply water-based paint.
Water-based paints have improved adhesion and give a matte (or satin finish) that is perfect for light metals, such as aluminum. Light metals develop scratches and marks easily, so you need a finish to hide these imperfections.
However, water-based paints are weak, not durable, water-soluble, and won’t protect the surface from anything. So, you must seal the finish with a waterproof sealant. You can use spar varnish or exterior polyurethane from this.
How To Paint Aluminum?
Painting non-porous aluminum is hard because the material doesn’t accept paint properly. So, you must create a textured layer over it to make it paintable.
Here are the tools you need:
- Self-etch primer
- Latex or acrylic spray paint
- Medium-grit sandpaper
- 400-grit sandpaper
- A portable vacuum or duster
- Enamel sealer
- Mineral spirits or turpentine
- A drop sheet
1. Prep The Aluminum Surface
First, prep the aluminum surface. This includes cleaning, degreasing, and removing fittings. Start by wiping it with a clean rag to remove dust and stains. For stubborn and greasy stains, pour mineral spirits into a rag and wipe the surface.
When the surface is clean, remove attachments and fittings from it. For instance, if you are painting an aluminum cabinet, remove the handles and metal fittings, so they don’t get stained. If you can move the item outdoors, do it.
If the aluminum is already painted (or finished), you must remove the finish. To do so, apply a paint stripper over the surface and scrape the paint off (using a plastic scraper). If the surface is painted with water-based paint, you don’t need to remove it. Instead, sand the finish with 150-grit sandpaper and apply a self-etching primer.
2. Sand it
Sanding will abrade the smooth aluminum surface, so it becomes textured and accepts paint. To sand aluminum, use medium-grit sandpaper (120-150-grit). After sanding, remove the dust and use a damp rag to clean it.
If you don’t sand, the primer or paint won’t stick, and the finish will peel off eventually.
3. Apply Self-Etching Primer
Use self-etching primer over aluminum. Self-etching primer is a two-in-one priming coat that contains a phosphoric acid ester that etches the aluminum and sticks over it. Other types of primer can’t stick over it.
Apply only one coat of primer. After the primer dries, sand it with 400-grit sandpaper.
4. Apply The Paint
To paint aluminum:
- Use a paintbrush or sprayer to apply the paint.
- If you use a sprayer, apply 3-4 coats. If you are brushing the paint, apply 3 coats.
- For exterior aluminum, use exterior latex or enamel paint.
- After the paint dries, seal it with exterior polyurethane or spar varnish (2-3 coats).
Painting Doesn’t Damage It
Painting aluminum doesn’t damage it as long as you use durable and protective paint. A durable and protective paint (or sealant) will prevent moisture from affecting it, so the aluminum won’t rust. If you use low-quality paint, the surface will get exposed to water, corrode, and turn brown.
Aluminum is one of the few metals that is naturally corrosion-resistant. This metal goes through a molecular change to develop a corrosion-resistant oxide coating. This coat prevents the surface from reacting to moisture and prevents rust or corrosion.
However, paint prevents this corrosion-resistant oxide coating from developing, meaning the material becomes prone to corrosion and rust. If you use protective and moisture-resistant paint (or sealant) this isn’t a problem. But, if you use weak paint, the aluminum will get exposed to moisture, and since it doesn’t have an oxide coating, the material will corrode.
Most of the paints aren’t moisture-resistant or have low resistance. That’s why you must seal them with waterproof sealant.
How Long Will The Finish Last?
A paint finish will last 5-10 years on aluminum surfaces or sidings. But, how long the finish will last depends on the type of paint (or sealant), and how much you use the surface.
For instance, the finish will last 5 years on high-traffic or exterior aluminum. That’s because the finish will be exposed to constant water and high traffic. On indoor surfaces, the finish will last 10 years or more because it won’t be exposed to elements that can damage it.
The maintenance and cleaning routine also determine the finish’s durability. Here are a few tips to make the paint last longer:
- Clean and maintain the finish regularly.
- Repair dents and damages on the aluminum before applying the paint.
- Always sand and prime before applying paint.
- Seal the surface with waterproof sealant.
In summary, painting over aluminum material can be tricky since it doesn’t accept paint well. However, you can sand it and apply self-etching primer to create a textured layer to which the paint can stick.
It’s recommended to use water-based paints (or matte finishes) since they hide stains, imperfections, and scratches from the surface. However, you must seal the paint with a waterproof sealant.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,