Painting Over Rust – a Full Guide

If you have railings or an iron gate in your garden that you’ve ever painted, you’ll know that painting over rust without taking the proper course of action will only lead to the paint failing after a very short period.

Rust is just the oxidisation iron in the metal, which is corrosive to the substrate and most types of paint. To prevent rust from returning you need to do two things. Firstly, you need to starve the affected areas of oxygen, which you can do with specialist products.  The second thing you need to do is block the stain from bleeding through, which some exterior paints do anyway.

In this guide, I’m going to talk through everything you need to know about painting over rust, and recommend the products you should use to complete the task.

 

Rust Primers

 

It’s easy to explain what rust primers do: they smother rust and starve it from oxygen, thus preventing it from coming back. They also help with adhesion and block the stain.

However, it doesn’t matter how good your primer is, if you don’t get your prep right then it will fail. Make sure you scrape any big patches of rust off first and remove any flaky paint. After you’ve done that, abrade with some aluminium oxide (sandpaper). Once you’ve done this, dust it off and you’re ready to paint.

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Red Oxide Primer

The first product I’m going to mention is red oxide primer. But instead of the old-school oil-based oxide primers we used to use over rust, nowadays you can buy a water-based version that works just as well, or even better.

I use Bedec All Metals Primer, and it hasn’t failed on me once. It’s quick drying, easy to use, great adhesion and it’s reasonably priced. You can’t go wrong really. Just ‘spot prime’ and rust patches prior to painting.

using a primer to paint over rust

Maston Anti Rust Primer

The other rust primer I use is an aerosol. Maston Anti Rust Primer comes in light grey, which is easier to paint over. It’s very easy to use as it gets into every little nook that you spray it at.

This has brilliant adhesion. I can only find one place online to buy it from, which is where the link below takes you. They also sell it in The Range, which is handy for me because I have a store around the corner from my house. (I know a Professional Decorator buying their paint from The Range sounds a bit odd, but it’s a great product and one I use often).

Rust Inhibiting Paints

 

There are some paint products designed for use on metal that have rust inhibitors in them. Hammerite claims to be one of them, but I can tell you from experience that if you paint over rust with Hammerite then it will fail within a few years.

In fact, I recommend using one of the above products to spot prime rust before painting with any paint, but it’s always reassuring to use a ‘finish product’ you know is capable of holding rust back.

Badite One Can would be my recommendation. It’s a fully water-based paint with fantastic adhesion qualities, rust inhibitors, and stain blockers.

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It’s another very modern paint, designed for use on multiple surfaces.

Opacity in white isn’t great, so expect to need an extra coat, but opacity in colours is spot on. It flies on too, and it’s quick drying. I used oil-based Hammerite for years and used to think it was fantastic, but modern paints like this are another level. They’re so much easier to use and they last a lot longer in my experience.

Final Thoughts

 

Easy really isn’t it. Ignore rust when painting and it will come back in no time. With a little bit of prep, a brush full of oxide primer, use rust inhibiting paint, and your exterior metal will look brilliant for years to come.

Painting Over Rust – a Full Guide – by Mike Gregory

Posted Sep 19, 2023 | 0 comments

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