Spray painting is known to give smooth and fine results when used on wood and ornaments. So, can you spray paint metal?
You can spray paint metal but the surface must be properly cleaned and sanded to get rid of dust, debris, and rust on it. You will also need to apply a coat of primer to allow the paint to adhere better.
Finally, you’ll need to use spray paint designed for metal as they are designed to last longer. It’s also advised to use a moisture-resistant and rust-proof finish to prevent the surface from turning brown.
Spray paints don’t stick properly to metal, especially to bare metal. Though spray paint will stay over it initially, the finish will quickly peel off after a few weeks. This happens for 2 reasons:
First, bare metal surfaces are usually slick and non-porous. This means the spray paint can’t penetrate them. Since it can’t penetrate, it won’t stick properly.
Secondly, metal surfaces are usually riddled with grime, dirt, and rust especially if they are placed outdoors. All of these will prevent a good adhesion. So, you need to clean, sand, and prime the surface first.
Cleaning and sanding helps to remove dirt and rust. While priming will produce a dry textured surface that will seal (cover) the slick surface of the metal and improve the adhesion of the paint.
It’s advised to use a self-etching primer as it will corrode the metal surface making it easier for the spray paint to stick.
Types of Spray Paint To Use
It’s recommended to use oil-based enamel spray paint for metal surfaces. They are durable and water-resistant meaning that the surface will be protected from moisture and rust. However, they will take longer to dry since the coating is oil-based.
Water-based acrylic paint is a great choice too, but it is better for indoor surfaces. Its bright color will go well on an indoor surface.
Spray paints specially designed for metal use, such as Rust-oleum or Krylon, can be used too. They are formulated to stick to metal surfaces. Krylon metal spray paint is designed with a built-in primer coating, so you don’t need a separate primer.
Rust-oleum spray paint has silicone compounds in the coating to shield the surface from heat and UV rays. Avoid using spray paints that have poor water and heat resistance as they won’t protect the surface and will expose it to different elements.
How To Spray Paint Metal?
Spraying metal isn’t hard, but you must do enough prep work to achieve a smooth finish.
Here are the tools you need:
- Clean rags
- Medium and fine-grit sandpaper
- Safety gear
- Drop sheet
- Paint shield
- Spray Paint
1. Scrape Existing Finish Off
If the metal has an existing finish, remove it. That’s because the existing finish is probably moisture-resistant and glossy, so it will prevent new coatings to stick over it. It also can bleed-through and discolor the new finish.
To remove it, use a paint-stripping compound and a putty knife. Apply the stripping compound over the surface, wait 10-15 minutes and scrape the stripping compound off the surface (the existing finish will come off too). Use mineral spirits to remove the stripping compound residue off the surface, and clean it with water.
Start sanding the metal with medium-grit sandpaper (150-grit). Ensure to sand all corners and nooks of the surface. For hard-to-reach spots, you can fold a sanding sheet to get to the tight spots.
Sanding with medium-grit sandpaper helps remove imperfections and rust while creating a textured surface for the paint to stick. After sanding with medium-grit sandpaper, use fine-grit sandpaper. This helps to even (flat) the surface so you can get a smooth result.
After sanding, clean and wipe the surface thoroughly.
3. Prime The Metal
To prime the metal, use a paintbrush to apply a coat or two of the primer. Wait for each coat to dry before applying the next one. The primer produces a dry textured finish over the surface that improves the adhesion. So, instead of the paint sticking to the metal surface, it will stick to the primer coating.
It’s recommended to use self-etching primer because it will etch or corrode the surface lightly so the paint can stick better. You only need one coat of it. You can also use water-based primer (2 coats).
4. Spray Paint The Metal
Once the surface is sanded, cleaned, and primed, spray it. If you are using spray paint (can), shake the can so the content inside can be properly mixed. If you don’t, the coating won’t have an even consistency or color.
Thin the paint if you are using a spray gun. That’s because the coating must be as thin as possible so it can fit the sprayer’s nozzle.
While spraying, keep at least 8 inches between the nozzle of the sprayer and the surface. Also, you should spray in a sweeping motion to prevent applying thick coats.
After spraying the first coat, let it dry properly. Depending on the spray paint, this can take between 30 minutes and 4 hours. When the first spray paint coat is dry, you can apply the second coat. You need 2-4 coats.
If the metal is placed outdoors, you must seal it to increase its durability. The sealant, when dry, will form a glossy moisture-resistant layer that will protect the finish from different elements. Exterior polyurethane or spar varnish are a great choice.
Blisters will show while and after spray painting if you don’t prep the paint and the surface correctly. Let’s check out a few tips on how to prevent them:
1. Don’t Over-shake
It’s advised to shake the spray can before using it to mix the content. But you shouldn’t over-shake it as you’ll create bubbles inside the can. Those bubbles will create blisters in the coating — so it’s best to avoid them. To prevent this, ensure to shake the can lightly for less than 60 seconds.
2. Clean The Surface
If there are debris and dust on the surface, you will notice blisters forming as the coating starts to dry. To prevent blisters, ensure to properly clean and wipe the surface.
3. Remove Rust
If there is rust on the surface, blisters are guaranteed to form as the coating starts to dry. You should remove rust by scraping and sanding the surface. You can also use rust-removal products if there’s too much rust.
4. Dry Time
On metal, you’ll need 2-4 coats of spray paint. Ensure that each coat dries fully before re-coating. If you re-coat too soon, the finish can develop blisters as moisture will be trapped in the coat underneath. Check the container of the sprayer to know how much to wait.
Preventing The Finish from Chipping Off
The finish will chip off only if the spray paint wasn’t applied correctly. Here’s how to prevent it:
- Prep The Surface – If you don’t clean the surface it will be filthy, and the filth will prevent good paint adhesion. Since the spray paint won’t stick well, it can easily chip off the surface.
- The Type – Not every type of spray paint can be used on metal. If you use a coating that has no moisture or rust resistance, the finish will be quickly affected by moisture and it can peel and chip off.
- Dry Time – If you re-coat too soon, the next coating won’t stick well so it can peel off. During high-humid conditions, you must wait 2 times more for the coating to dry than normal.
- Thick Coats – If the coating is too thick, it can develop cracks that will cause it to peel off gradually.
- Fast Dry Time – If the finish dries too fast, the particles don’t have enough time to harden and compact so the finish will peel off.
Things To Know
Painting Over it
You shouldn’t spray paint over painted metal. This is because the metal finish is usually oil-based and will prevent a new coating from sticking over it. Also, the finish is usually moisture-resistant, meaning it will prevent liquids from penetrating its coating.
You will have to sand off the finish first before painting over it.
On average, spray paint will last 5 years on metal before you notice any imperfections or changes in the finish. The reason the finish lasts longer is that spray paints designed for metal are usually oil-based and have moisture-resistant features. These features will help the finish thrive under harsh conditions.
In summary, you can spray paint metal but you have to prep its surface by cleaning, sanding, and priming. These three things will improve the adhesion and help the finish last longer. If you don’t prep it, the coating won’t stick well and the finish might peel off.
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,