No one likes the look of rusted metal. So, can you paint over rust to cover it?
You can paint over rusted metal if the rust didn’t damage the metal surface. In this case, remove the loose rust by sanding, clean the metal, and apply paint.
However, if the rust has eaten through the metal or created holes and dents in the metal frame, you shouldn’t paint over it because the paint will not stop the rust from spreading. In this case, the best thing to do is to either fill the holes in the metal or replace the metal altogether.
This post reveals more about painting over rust, including a 5-step method to carry out the task. So, let’s dive in.
Do You Need To Remove Rust Before Painting?
You must remove rust before painting. That’s because rust (or iron oxide) is a loose material. So, if you paint over rust, the loose material will cause cracks and splits on the paint coating once it dries.
Also, since there’s rust on the surface, the paint won’t stick properly to the surface. Instead, the paint coating will stay over the rust material leading to poor adhesion between the paint coating and the metal.
The reddish-brown substance known as rust is made from the reaction of iron, oxygen, and moisture or water. When metal is exposed to constant moisture and air (oxygen), the reddish-brown substance (rust) starts forming on the metal’s surface.
Rust is flaky and weak and can break down under minimal contact. When you apply paint over rust, the flail structure of rust won’t be able to support and carry the paint coating. Instead, rust will break into small pieces underneath the paint and cause cracks and splits on the paint coating. After a while, the entire paint coating will peel and fall off the metal surface. That’s why you should remove rust before applying paint.
To remove the rust, scrape it off the metal and sand down the metal with sandpaper. Afterward, you must wipe and clean the metal surface to get rid of leftover rust. When the metal is smooth and rust-free, you can apply the paint. Optionally, you can also apply primer on metal before applying paint.
Does Paint Stop Rust?
Painting can stop rust only if the rust hasn’t penetrated the metal frame. Painting will cover the metal surface and prevent rust from growing.
However, if rust has penetrated the metal surface, painting won’t stop it. In this case, the damaged metal will continue to release rust and metal shavings underneath the paint coating and cause the paint to blister and come off.
Rust is caused by two major factors; moisture (or water) and oxygen (or air). When a metal surface is exposed to these two factors, the iron compounds in the metal will react and form iron oxide (rust). However, if you apply moisture-resistant paints over metal, the paint will shield the metal from air and moisture, preventing rust from growing.
Since paint protects metal from air and water, the rust will stop growing. So, painting stops rust, but only if the rust has affected the surface of the metal and not the metal frame.
If rust has penetrated the metal frame, painting won’t stop rust. That’s because if rust has penetrated the metal frame, it means the frame is weak and has holes. So even if you paint over it, the weak metal frame will still release rust and metal shavings underneath the paint, causing the rust to spread and damage the paint.
Sanding and Priming are Necessary
Can you paint over rust without sanding or priming? You can’t. You must sand and prime.
Sanding helps to remove loose rust particles on metal, so you can’t paint over rust without sanding.
So if you apply paint over rust without sanding, there will still be loose rust on the metal which will cause the paint to crack and peel off. So, sanding is not optional when you want to paint over rust.
Here is a list of things that will happen if you apply paint on rusted metal without sanding first:
- The paint will not stick to the metal as it should.
- The paint coating will be affected by stains and can eventually turn brown, especially if the paint is transparent.
- The paint coating will take longer to dry.
- The paint coating will blister and eventually fall off.
You can paint over rust without priming, but the metal has to be clean and rust-free for you to skip primer paint. Also, you must use paint designed for metal if you don’t want to prime.
Priming helps paint to stick better to rusted metal. However, the paint will stick properly without primer if the metal surface is rust-free and clean. However, you must use paint designed for metal, such as rust-oleum, because these paints stick better to bare metal. This way, the paint will stick well to the metal surface without a primer coating.
How To Paint Over Rust?
You need a few tools to make the process easier:
- A scraper or trowel
- Primer paint for metal
- Auto body filler
- Clean rags
- Breathing protection
- A pair of work gloves
- Metal paint
1. Scrape Off The Rust
Remove as much rust as you can from the metal surface. To do this, use a flat metal object like a putty knife or trowel.
Using the putty knife, scrape off as much rust as you can. You don’t have to remove all the rust using this method; just remove the loose rust.
Important: Wear gloves and a face mask before scarping rust.
2. Sand The Rusted Metal
After removing most rust using a scraper, remove the leftover rust particles using a sander.
To sand rust, use fine-grit sandpaper. Sandpaper can get dull fast from sanding metal, so get as many sandpapers as possible. Instead of sandpaper, you can also use a power sander.
3. Wipe and Clean The Metal
Sanding produces a lot of dust, so you must wipe and clean the metal with vinegar. Vinegar is a mild acid that will dissolve and remove filth and reddish tints from the metal surface. Baking soda and rubbing alcohol also work in case you don’t have vinegar. If you don’t clean the metal surface, the finish will appear reddish or brown due to the effects of rust.
To clean the metal, damp a rag with vinegar and use the dampened rag to clean the surface. You can also pour vinegar directly on the metal surface and use a rag to wipe the surface.
4. Fill Holes In The Metal (Optional)
If rust has weakened the metal and created holes, you must fill these holes with auto body filler. The auto body filler is a paste-like product that helps to cover and seal holes in metal surfaces.
If you don’t cover the holes in the metal, the paint will be sucked into the metal frame and won’t appear smooth.
5. Apply A Coat Of Primer Paint Over The Metal
Once the metal is rust-free, cleaned, and sanded, apply 1-2 coats of primer. The primer must be designed for metal surfaces. To apply primer, use a paintbrush.
6. Apply The Paint
Once the primer dries, apply paint over the metal surface. You must apply paint designed for metal surfaces because these paints will prevent rust from growing again.
To apply paint, use a paintbrush or a spray gun. You must apply 2 coats of paint over the metal. Wait for the first coat to dry before applying the next one.
Is There A Paint That Kills Rust?
Technically, no paint will kill rust because rust will develop as long as the metal is exposed to moisture and air. However, some types of paint prevent rust from growing and spreading on metal.
These paints are formulated to be thick, moisture-resistant, and heat-resistant. Using such paints over metal will prevent rust from affecting the metal surface. An example of such paint is rust-oleum paint.
Can Rust Bleed-Through Paint?
The best way to prevent rust from bleeding through the paint is to scrape the rust off, clean the metal surface with vinegar, and applying primer paint.
When you scrape the rust off and clean the metal surface with vinegar, you remove rust particles that can bleed through the paint. Primer will seal the metal surface and prevent rust from bleeding through too.
You can paint over rusted metal as long as the rust hasn’t completely damaged the metal frame. However, you must remove the rust, wipe the surface with vinegar, and apply primer and paint.
However, if the rust has eaten into the metal frame, you must fill the holes and dents in the metal with auto body filler before applying the paint. This will ensure that the paint sticks properly to the rusted metal.