Get all the rust, or it will eventually get you

From the moment they leave the retailer's lot, our vehicles start on the road to rust. And because Canadians keep their vehicles for about a decade on average, and drive in environments that are the least hospitable for automotive metal, chances are good that some level of corrosion will take its toll on those vehicles.

Many do-it-yourself types tackle non-structural rust repairs to try to extend the working life of their vehicles, or just to keep them looking good. Different types of rust, or rust in different locations, require different approaches to successfully beat the oxidation beast.

Surface rust: This is the type that most often occurs first, usually on outer body panels, and most often as a result of some type of impact or scrape that breaks the paint and exposes the metal underneath. Many car owners simply do a cursory cleaning of the area, and then reach for a paint stick to touch things up. But if the paint around the chip or scratch has started to bubble up, then there's enough surface corrosion to keep spreading.

This is when the abrasives have to come out. You need to remove all traces of rust, and then treat the area with a rust inhibitor that will convert any remaining microscopic rust into a more stable compound. Inhibitor compounds, such as those with tannic acid, are needed before you get to priming and repainting.

Scaling rust: This refers to the condition where the rusted metal peels or flakes off, leaving the area under it freshly exposed to another round of corrosion. It may occur on thicker structural vehicle components, such as frame rails or cross-members. As with serious surface rust, if you don't get all the corrosion cleaned off, it will return, no matter how well it's sealed up afterwards. If it's on the undercarriage, make sure you clean enough area around it to reapply any undercoating treatment the vehicle had on it. On structural metal, test the strength of the area first by tapping it with a hammer to see how much force it takes to dent it. If it gives too much, you may need to replace that part.

Perforation: Perforation on sheet metal can really only be properly tackled by replacing the panel, or by cutting out all the rusted metal and weld-patching in new material.

This type of repair should not be used if the holes are in a structural component, as it will reduce or change the strength of that part. In a collision, its performance will be questionable at best. This requires replacement instead.