In Montreal, the City spreads an average of 150,000 tonnes of salt per winter on more than 10,000 km of streets and sidewalks. Province-wide, Quebec's Ministère des Transports reports more than 1.5 million tonnes of road salt per year. All that salt ends up on the roads, then under cars, on trailers, handrails and guardrails.
What salt does to metal
Rust needs water and oxygen. Salt speeds everything up: chlorides from de-icing salts accelerate the corrosion of steel and zinc, especially in joints and overlaps where moisture stays trapped, notes the American Galvanizers Association. Aluminum does not rust, but it is not immune. Under paint, filiform corrosion traces fine filaments starting from a scratch or a chip, as described by Products Finishing. And aluminum in contact with steel, in salt water, corrodes through galvanic action.
Three lines of defence
The first is invisible: pretreatment. It is what keeps corrosion from running under the film when the film is cut. Specialists say it again and again about filiform corrosion: prevention depends on pretreatment and adhesion. The second is the film itself, a continuous barrier against water and salt. The third concerns edges: as it melts, powder thins out on sharp corners, which become the weak point, as a technical article from PPG explains. For highly exposed parts, manufacturers call for a primer under the colour coat.
What we do, and what you can do
Every part is degreased, rinsed and pretreated with zirconium, then receives up to three coats depending on its use. For a chassis part or winter wheels, say so in your quote request: a primer can be added. On your end, two habits extend the life of the finish: rinse off the salt regularly during winter and touch up without delay any chip that exposes the metal.
In summary
- Montreal spreads an average of 150,000 tonnes of salt per winter; Quebec, more than 1.5 million tonnes per year.
- Salt speeds up the corrosion of steel and does not spare aluminum.
- Pretreatment, a continuous film and edge protection make up the defence.
- Rinsing off salt and touching up chips extends the life of the finish.
