Can You Paint Over Rust? (Explained!)

No one likes the look of rusted metal which is why many DIYers wonder if they can cover the rust by painting over it. So can you paint over rust? Here is the answer.

You can paint over rusted metal as long as the rust is only affecting the surface of the metal. In this case, you just need to remove the loose rust by sanding and cleaning the metal before applying the 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?

Do You Need To Remove Rust Before Painting?

You need to remove rust before painting. This is because rust or iron oxide is a loose material. If you paint over rust directly, the loose material will give way causing cracks and splits in the paint coating.

Also, applying paint over rust directly means that the paint will not stick to the surface. Instead, the paint coating will stay on the rust material leading to poor adhesion between the paint coating and the metal.

It’s generally advised to remove rust from metal surfaces before applying paint. This is because of the structure of the metal rust. 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 starts to form on the surface of the metal. This reddish-brown substance is usually flaky and weak which means that it can easily break down under minimal contact.

So when you apply paint directly on rust, the frail structure of the rust will make it unable to support and carry the paint coating. Instead, the rust will break into smaller pieces underneath the paint causing cracks and splits in the paint coating. After a while, the entire paint coating will peel and fall off the metal surface. This is why it’s generally advised to remove rust before applying paint.

To remove the rust, you can scrape it off the metal and then sand down the metal with sandpaper. You’ll also need to wipe and clean the metal surface afterward to get rid of any leftover rust. When the metal is smooth and rust-free, you can apply the paint. Priming the metal before applying the paint also helps the paint to stick better.

Will Painting Over Rust Stop It?

Painting over rust will stop it as long as the rust hasn’t eaten into the metal frame. This is because the paint coating will cover the metal surface and protect it from factors causing it to rust.  

However, if the metal is severely affected by the rust, painting over it will not stop the rust completely. In this case, the damaged metal will continue to release rust and metal shavings underneath the paint coating and eventually 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, when you apply paint over the metal surface the paint coating will shield the metal from air and moisture. Water-resistant paints especially will prevent water and air from getting to the metal underneath.

Since the metal is protected from air and water, the rust is automatically halted. So in this case, the paint will stop rust. However, this only works when the rust has only affected the surface of the metal.

If the rust has eaten into the metal frame, painting over it will not stop the rust. This is because for the rust to have eaten into the metal frame, it means that the metal frame has become weak. In this case, the rust would have caused holes in the metal frame. 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 eventually damage the paint.

Can You Paint Over Rust Without Sanding?

You can’t paint over rust without sanding. This is because sanding helps to remove the loose rust particles on the metal.

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 eventually peel off. 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 not dry quickly
  • The paint will smell like metal shavings
  • The paint coating will blister and eventually fall off.

Can You Paint Over Rust Without Priming First?

You can paint over rust without priming first but the metal has to be completely clean and rust-free for you to skip primer paint. Also, you are to use paint designed for metal if you don’t want to prime.

The purpose of priming rusted metal before applying paint is to make the paint coating stick better to the metal surface. However, you can skip primer paint but to do this, you need to ensure that the metal surface is completely rust-free and clean.

Also, you have to use paint designed for metal such as rust-oleum paint as such paints will stick to the bare metal. This way, the paint will stick well to the metal surface even without a primer coating underneath.

Next, let’s check out how to paint over rust easily.

How To Paint Over Rust?

Painting over rust is a fairly easy task but you have to follow the right steps to achieve a smooth and clean result. This guide will show you how to paint over rust in just six simple steps. But first, we need a few supplies and tools to make the task easier:

  • A scraper or trowel
  • Primer paint for metal
  • Auto body filler
  • Sandpaper
  • Clean rags
  • Vinegar
  • Breathing protection
  • A pair of work gloves
  • Metal paint

Here is a 6-step guide to painting over rust:

1. Remove The Rust

Remove The Rust

The first step is to remove as much rust as you can from the metal surface. To do this, you should use a flat metal object like a putty knife or trowel.

Use the trowel to scrape the rust off repeatedly. Ensure to put on a pair of gloves and a face mask before doing this to prevent injuries. The face mask helps to stop you from inhaling rust particles in your lungs as you scrape the rust off.

You might not be able to scrape off all the rust from the metal but don’t worry. The next step will take care of the leftover rust particles.

2. Sand The Rusted Metal

Sand The Rusted Metal

After removing the rust, you are sure to have leftover particles on the surface. The metal surface will also be rough after scraping the rust off.

So you need to sand down the metal to get rid of rust particles and to smoothen the metal surface. You are to sand with fine-grit sandpaper but ensure to get many packs of sandpaper as the grit can quickly get dull from sanding metal.

3. Wipe and Clean The Metal

Wipe and Clean The Metal

With the metal surface properly sanded, you are to wipe and clean the metal with vinegar. This is to ensure that the metal is clean before the paint is applied.

If you don’t clean the metal surface, it will appear reddish or brown due to the effects of the rust. 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.

4. Fill Holes In The Metal (Optional)

Fill Holes In The Metal

If there are holes or dents in the metal as a result of rust, you need to 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 it will never appear smooth.

5. Apply A Coat Of Primer Paint Over The Metal

Apply A Coat Of Primer Paint Over The Metal

After the metal has been wiped with vinegar, use a wet rag and little soap to wipe the metal. This helps to remove leftover vinegar that can etch the metal.

When the metal gets dry, you can apply a coat or two of primer paint. Ensure to use a primer that is designed for metal surfaces.

6. Apply The Paint

Apply The Paint

When the primer gets dry, you can apply the paint over the metal. It’s best to use paints designed for metal surfaces as such paints will prevent rust later.

You can apply the paint either with a paintbrush or a spray gun. After applying the paint, ensure to leave it to dry fully before using it.

Will Rust Spread Under Paint?

Rust will not spread under paint unless the metal frame has been severely affected by the rust before the paint was applied.

If there are holes and dents in the rusted metal, then painting over it will not stop the rust because the metal frame will already be weak. In this case, the rust will continue to spread even after the paint has dried.

However, if the rust only affected the surface of the metal, then it will not spread underneath the paint coating since the metal frame will still be strong.

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, there are certain types of paints that will prevent rust from growing or spreading on metal.

Such 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.

How To Prevent Rust From Bleeding Through Paint?

The best way to prevent rust from bleeding through the paint is a 3-step method and this includes scraping the rust off, cleaning the metal surface with vinegar, and applying primer paint.

When you scrape the rust off and clean the surface with vinegar, you directly remove any rust particle that can bleed through or stain the paint coating. The primer coating will complete the process by sealing the metal surface and preventing any sort of bleed-through.

Final Words

In summary, you can paint over rusted metal as long as the rust hasn’t completely damaged the metal frame. All you need to do is remove the rust, wipe the surface with vinegar, and apply the paint.

However, if the rust has eaten into the metal frame, you need to 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.

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