Applying fresh coats of paint on aluminum is a great way to add color and beauty to the aluminum surface. However, painting an aluminum surface is often difficult because aluminum is a slick and non-porous material.
Since the material is non-porous, paint regardless of the type can’t penetrate and as such will not stick to aluminum. So, to make the paint stick to aluminum, you need a different painting method which is discussed extensively in this post. You’ll also learn:
- How to paint aluminum?
- What primer to use on aluminum?
- How to make paint stick to aluminum?
- How to make a paint finish last longer on aluminum?
Let’s dive in.
Do You Have To Sand or Prime Aluminum Before Painting?
You have to sand and prime aluminum before painting because aluminum will not accept any paint without a primer coating. For paints to stick to a surface, the paint has to bite into the surface to stick.
However, the slick and non-porous surface of aluminum prevents paints from biting into the surface meaning that the paint will not stick. This is why sanding and priming are required before painting aluminum.
Sanding helps to abrade the aluminum coating so it becomes textured. Since the surface is textured and not slick, the paint can bite into it and stick better.
The primer coating also provides a smooth undercoat for the paint to sit on. This ensures you have a smooth finish. Priming also improves adhesion between the paint coating and the aluminum surface.
How To Paint Aluminum?
Since aluminum is non-porous, the material doesn’t accept paint properly. So, the bulk of the work that you’ll be doing is prepping the aluminum surface to make it paintable.
When the aluminum has been prepped, you can paint it. This guide will show you how to complete the task in 5 simple steps. But first, you’ll need the following tools and supplies:
- 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
Here is a 5-step guide to painting an aluminum surface:
1. Prep The Aluminum Surface
The first step to painting aluminum is to prep the surface. This includes cleaning, degreasing, and removing fittings on the aluminum. Start by wiping the aluminum surface with a clean rag. This helps to remove dust and stains. For stubborn and greasy stains, you can wipe the aluminum with a clean rag and mineral spirits.
When the surface is clean, remove all attachments and fittings on it. For instance, if you are painting an aluminum cabinet, you need to remove the handles and metal fittings so they don’t get stained by the paint.
If you can take the aluminum item outdoors, you should. This prevents paint fumes inside the home. But if you can’t remove the aluminum to take it outside, you should open all doors and windows for improved ventilation. Also, place a large drop sheet on the floor to collect dust and paint splatters.
2. Sand The Aluminum Surface
The next step is to sand down the aluminum surface. This step helps to abrade the smooth aluminum surface so it is textured and easier to paint over.
If you don’t sand, the primer and paint will not stick and will peel off the surface in weeks. You should sand the aluminum with medium-grit sandpaper. 120-grit to 150-grit sandpaper will work fine.
After sanding, remove the dust on the aluminum with a duster or vacuum. You can also use a clean rag. If you don’t remove the dust, the finish will be riddled with bumps.
3. Apply Self-Etching Primer
With your aluminum surface properly prepped, cleaned, and sanded, you can apply a coat of the primer paint.
The best type of primer to use on aluminum is self-etching primer. Self-etch primer is a two-in-one priming coat that etches the aluminum and primes it for paint. The reason this primer is the best on aluminum is that it contains phosphoric acid ester which causes it to bite into the aluminum surface and stick when other primers can’t.
You only need one coat of self-etch primer on the aluminum. Ensure to put on a face mask when spraying the primer so you don’t inhale fumes. After applying the self-etch primer, wait at least 3 hours before sanding lightly with 400-grit sandpaper. Then remove the dust with a vacuum.
4. Apply The Paint
The next step is to apply the paint to the aluminum surface. You can do this using a paintbrush or a paint sprayer but spraying the paint guarantees improved coverage and adhesion.
Spraying is also faster than brushing the paint and you wouldn’t need to deal with brush marks. If you are spraying, you need 3-4 coats of paint on the aluminum. If you are brushing the paint on, don’t apply more than 3 coats.
If you are working on an exterior aluminum surface, you should use an exterior latex or acrylic paint. You should wait 1 hour between coats of latex and acrylic paint.
5. Seal The Paint
The final step is to seal the paint on the aluminum surface. Sealing the paint protects it from scratches, fading, moisture, and damage.
Sealing also protects the aluminum surface. You can seal the paint with coats of enamel sealer. It takes at least 24 hours for enamel sealer to dry so give enough dry time before using the aluminum surface.
Does Painting Aluminum Damage it?
Painting aluminum doesn’t damage it as long as you use a durable and protective paint on the aluminum surface. Painting aluminum can only cause damage if the paint is weak and if the finish is breached. When this happens, the aluminum surface will suffer corrosion and will turn brown.
Aluminum is one of the few metals that is naturally corrosion-resistant. Aluminum goes through molecular changes to develop a corrosion-resistant oxide coating. This coating changes the molecular structure of the metal so it doesn’t react chemically to moisture and oxygen which can cause rust and corrosion. This is why aluminum can maintain its look for years without being corroded.
Now when you apply paint on the aluminum, the paint coating prevents the aluminum from developing its corrosion-resistant oxide coating which means the metal will now become prone to corrosion and rust. However, this isn’t a problem since there is a durable paint coating on the aluminum metal.
As long as the paint is durable and in good condition, then the aluminum will remain corrosion-free because it is protected by the paint but if the paint starts to crack or split, then there is a problem and risk of damage to the aluminum.
When the paint gets cracked, moisture and oxygen will get in and since the aluminum doesn’t have its corrosion-resistant oxide coating anymore, it will get damaged. In summary, the aluminum will only get damaged when painted if you use weak paint or if the paint gets damaged.
What Kind Of Paint To Use On Aluminum?
The best paint to use on aluminum is latex or acrylic paint. These are water-based paints that dry quickly. The reason water-based paint is ideal for aluminum is that it doesn’t highlight scratches and imperfections on the aluminum. If you use oil-based paint on aluminum, the glossy finish will highlight stains and imperfections on the metal surface.
Water-based paints generally work better on aluminum because water-based paints have improved adhesion, dry quickly, and give a matte or satin finish. All these qualities are great for aluminum. The quick dry time allows you to apply more coats in time and the improved adhesion allows the paint to stick to aluminum which for the record, doesn’t accept paint well.
Water-based paints also give a matte finish which is perfect for a light metal like aluminum. Being a light metal, aluminum develops scratches and marks easily so you need a finish that will hide the scratches and water-based paints do this perfectly. If you use oil-based paint or a high-gloss finish on aluminum, the scratches and marks on the metal will become very visible.
Can You Paint Over Already Painted Aluminum?
You can paint over already painted aluminum. To do this, start by inspecting the existing paint on the aluminum surface.
If the existing paint was sealed with a topcoat, then you’ll need to strip the sealant before applying new paint. This should be done with a paint stripper. If the existing paint wasn’t sealed, then you don’t need to strip the finish. Instead, sand the existing finish with 150-grit sandpaper and finish with 220-grit sandpaper.
After sanding, remove dust and apply a coat of self-etch primer on the aluminum before applying new paint. You should know that if the existing paint is oil-based, then you’ll need to remove it before applying new paint. This is because oil-based undercoats don’t work well on aluminum.
Here is a step-by-step guide to painting over already-painted aluminum:
- Inspect the finish and remove the sealant.
- Sand down the aluminum with a medium and fine-grit sandpaper.
- Remove dust with a vacuum.
- Apply a coat of self-etch primer and wait 3-4 hours for it to dry.
- Scuff the primer coat with ultrafine sandpaper.
- Apply new paint and leave it to dry.
How Long Does Paint Last on Aluminum?
Paints last 5-10 years on aluminum surfaces including aluminum siding. How long the paint lasts depends on the type of paint, how durable the paint is, and where the paint was used.
On busy surfaces and exterior aluminum, paints last 5 years or less. This is because the paint will be exposed to high traffic and heavy abuse.
On indoor aluminum and low-traffic areas in the home, the paint can last up to 10 years on the aluminum since the finish will not be exposed to traffic or heavy abuse. You should also know that the maintenance and cleaning routine of the paint determines how long it will last.
However, here’s a few tips that you can use to make paint last longer on aluminum:
- Clean and maintain the finish regularly.
- Repair dents and damages on the aluminum before applying the paint.
- Always sand and prime the aluminum before applying paint.
- Seal the paint when it dries – Sealants protect paints from damage.
- Don’t subject the paint to harsh use or chemical spills.
In summary, painting over an aluminum surface can be tricky but it’s not impossible. Before applying the paint, you should wipe, clean, and degrease the aluminum surface to remove grime. Then you should sand and apply a self-etch primer coating before applying the paint.
Ensure to only use water-based paints and matte finishes on aluminum to hide stains and scratches on the metal. Finally, if the aluminum has an existing paint, you need to sand and prime it before applying a new paint coat.