Removing rust from your car takes four stages: sand the loose rust back to bare metal, convert what remains with a rust converter, prime the metal and finish with paint or rust protection. Skip a stage and the rust spots on your car usually return within a season.
Rust is rarely only where you can see it. Under a bubble in the paint the steel is often further gone, so you always work beyond the visible spot. Below you will find which approach suits which rust, then the step-by-step plan and the mistakes we see most often in the workshop.
Rust spots on your car: which approach fits?
First work out which rust you have. Orange specks on the paint are a different job from a bubble in a sill or a rusting weld seam. A rust remover that works on paint is not the same as a product that converts rust in steel.
Type of rust | Approach | Product |
|---|---|---|
Orange specks on the paint (fallout) | Remove chemically, do not sand | |
Rust bubble or light rust on steel | Sand back to bare metal | |
Deeper rust with pitting | Brush, then convert | |
Weld seam, panel edge or bare steel | Etch primer or zinc primer | |
Cavities and underside (prevention) | Corrosion inhibitor mixed with water | |
Rusted-through panel | Replace the metal or weld, then prime | etchweld after welding |
How to do it
Expose the spot. Sand or brush away all loose, flaking rust and paint until you see sound steel. A non-woven disc such as the Clean and Strip removes rust and paint without attacking the metal underneath, and its mandrel fits a drill or angle grinder. For seams and edges use a Monti MBX Sanding Belt Coarse Black. Tip: go a few centimetres past the visible edge, because the rust is already working under the paint there.
Clean and degrease. Vacuum up the dust and degrease the area thoroughly. For Hydrate 80, Bilt Hamber names degreasing as a condition: grease residue leaves flaws in the film. Rinse with clean water afterwards and let the spot dry fully.
Convert the remaining rust. Shake Hydrate 80 well and pour some into a non-metallic container. Apply it sparingly with a brush, work it into the pits and smooth it in one direction. After about 30 minutes add a second coat at right angles to the first. Tip: never pour leftovers back into the bottle, and do not work below 10 degrees, because the reaction slows down. No rinsing afterwards is needed.
Let it cure. For the best result wait 24 hours before finishing. If you need to move faster, a coat can usually go over it after about three hours. Tip: you may flat the converter lightly, but never through the layer.
Prime the metal. Give Electrox one full coat without brushing it over and over: it is surface dry after 20 to 30 minutes and hard dry after about three hours. Stir it well first and while you work, so the zinc stays mixed in. Choose etchweld when you still have welding to do or paint has to go over it. Shake the aerosol for at least two minutes; stir the pail thoroughly and thin it with up to 50 percent cellulose thinner if needed. For small spots the can is handy, you will find those under spray can and primer.
Finish and protect. Feather the edge of the repair with Mirka Abranet P180 and then paint in the colour of the car. If the spot is on the underside, a brush-on coat such as Motip Anti-Gravel Underbody Protection White against stone chips is a good finish. Mix Atom-Mac at 2 to 5 percent in water and spray it on the underbody.
Common mistakes when treating rust
Only treating the visible spot. Rust keeps working under the paint, so always go past the edge.
Putting a rust converter over loose, flaking rust. The active ingredients have to reach the steel, so brush or sand first.
Skipping the degreasing. Grease leaves little craters in the film, and that is where the rust starts again.
Applying too thickly. Thin in two coats works better than one thick coat.
Spraying straight over the converter without testing. Paint systems differ, so try a small area first.
Doing nothing about the rest of the car after the repair. Sills, wheel arches and cavities deserve the same attention.
Protecting the metal after removing rust
A treated spot is only finished once it is protected. How to preserve the underbody, cavities and visible parts is covered in the guide to rust prevention and underbody protection. More on converting existing rust is in the guide to Hydrate 80, and on the zinc-rich primer in the guide to Electrox. Everything for rust protection is under rust protection and preservation, the sanding supplies under sanding discs and paper.