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Rust on vehicles could be a result of salt brine; here’s how to stop it

January 13, 2019
The city of Idaho Falls uses a 50-50, sodium chloride/sand mixture on select city roads prior to a snow event, which will make it easier to remove snow and improve driving conditions. The salt brine and sand are of obvious benefit to drivers, but less obvious is the damage salt can do to their vehicles over time.

When snow starts to fall in Idaho Falls, the city’s Street Division has already been active for hours, laying down salt brine.

The city uses a 50-50, sodium chloride/sand mixture on select city roads prior to a snow event, which will make it easier to remove snow and improve driving conditions.

The mixture is applied to “Priority 1” roads, or arterial and major collector streets, and “Priority 2” roads, or minor collector streets.

“This application helps prevent the bonding of snow and ice to the road surface on these higher priority streets,” city of Idaho Falls spokeswoman Kerry Hammon said in an email. “The sand helps provide traction.”

The salt brine and sand are of obvious benefit to drivers, but less obvious is the damage salt can do to their vehicles over time.

Rich Frerichs, 50, of Idaho Falls, regularly maintains his 2009 Dodge 2500 truck. Last year, he installed a new exhaust pipe, which has since become rusty, a corrosion of metal that he attributes to salt brine.

“It’s just nasty stuff,” Frerichs said. “It is terrible for cars. It makes it rust faster, corrode faster. It really does a job.”

The ball hitch on Frerich’s car also is encased in a layer of rust, and chips in the paint on his truck rusted faster than they should have, he said.

The rusted metal on Frerich’s car could be the result of a simple chemical reaction, as salt meets metal surrounded by moisture, according to Krishnan Raja, Ph.D., an associate professor in chemical and materials engineering at the University of Idaho.

“Chloride and metal, they don’t go together well,” Raja said.

Metal has an oxide layer that typically would protect it from corrosion, but chloride will break down that protective layer, which leads to rust, Raja said.

Salt alone doesn’t create rust; it also requires moisture.

Think of all the rusty cars in beach towns. Moisture, mixed with salty air from the ocean, is a perfect recipe for rust. Salt brine mixed with humidity can create the same effect.

While eastern Idaho is typically dry and cold in the winter (not ideal conditions for humidity), a vehicle, covered in snow and salt and parked in a garage, will create the right conditions for rust. That enclosed space will trap humidity and the mixture could slowly eat away at the metal.

“As the temperature increases the corrosion is going to increase,” Raja said. “The corrosion is going to be slow.”

The city has been using the salt-sand mixture for about three decades and it won’t be changing the mixture anytime soon, it seems, due to the high cost of alternatives.

“There are some other materials available that claim to (be) better on vehicles, but they are about 10 times the cost of the current mixture,” Hammon said.

There are ways to protect a car from the damage salt brine could cause.

Raja recommends car owners avoid parking in the garage if they just drove through salt brine.

It’s also a good idea to wash a car if it’s covered in salt, he said.

Hammon said city snow removal vehicles aren’t damaged from salt brine, however they are occasionally washed after a snow removal operation.

“Similar to what the city does for our own vehicles, we recommend periodically washing your vehicles using one of the local car washes,” she said. “There are several automatic car washes that do a great job removing salt, sand and other dirt associated with driving in winter conditions.”

Corrosion inhibitors or rust protectant, which can be purchased at automotive parts stores, can also be useful, Raja said. Those act as shields to block chloride from corroding metal.

“These are basically organic solvents,” Raja said. “They stick to the surface and they avoid contact with the chloride.”