Maintenance Q&A
The nitty gritty on NaCl

Q. Is there a difference between the salt on the road and the salt in the shaker on your table?

A. Chemically, the majority of the salt used to fight ice and snow is the same as table salt, but it differs physically. While both are sodium chloride (chemically NaCl), table salt is processed for size and purity fit for human consumption.

Rock salt, commonly spread on roads, is taken from the mines, crushed and screened to have some bulk to slow its dissolving when mixed with ice and snow and to improve traction.

Ice’s freezing point depends primarily on the concentration of the salt and the temperature of the air and the road. Early in winter, the ground may be warm compared with air temperature, and less salt or more benign salt will work. But after a long cold snap, the ground may be so cold that even after a warm day it is cold enough to freeze rain. In that case, rock salt provides some grip but does virtually nothing to melt the ice.

The salt dissolves into the ice or snow, mixing to form a solution. A 10 percent concentration will freeze at 20 degrees, while a 20 percent concentration is good down to 2 degrees. Rock salt is only effective by itself at 15 degrees or higher.

To increase the effectiveness sand is added for traction along with other types of salt. These include magnesium and calcium chlorides, and to a lesser extent potassium chloride.

Pure calcium chloride works in temperatures as low as 25 degrees below zero. Calcium chloride draws moisture from the air. It’s used on dirt roads to control dust. But when used on paved roads, it contributes to corrosion.

Road departments used to stage idling salt trucks along the roads when snow or freezing rain were forecast. To cut fuel costs and avoid overtime, departments started spreading brine, urea and acetates in advance of the weather. They slowly dry, leaving a coating on the roads that melts the precipitation when it hits and provides snow control until plows can be dispatched.

The liquids also leave films on the roads. As cars and trucks drive over the damp films, they kick up a spray that finds its way into many components of our vehicles, trucks and cars alike. That’s why winter maintenance applies to all motor vehicles, not just trucks.

Because the salts, brines and other liquid chemicals are easier and more economical to apply, their use is increasing. But because of corrosion states are researching less aggressive materials. One showing great promise is beet juice. Its sugars go into solution and lower water’s freezing point, but do not attack metals as aggressively.

Until totally benign chemicals are universally accepted and salts are no longer used, take steps to protect your truck’s most vulnerable areas.

Wash it regularly, using power washers if possible, and soon after driving through areas of heavy salt use. Steam clean your undercarriage at least monthly in winter. The steam will get into crevices where road spray congregates and that brushes can’t reach.

Seal your electrical system. Use dielectric grease on all connections. Take ground wires back through the 7-pin harness to the battery, not to sheet metal screws on the chassis. Better yet, specify sealed wiring harnesses on new trailers and rewire trailers already in service. If you must splice wires, use connectors with heat-activated sealant and cover them with heat-activated shrink tubes.

Make sure dissimilar metals – aluminum cross members and steel chassis rails, for example – are isolated from each other with Mylar film or other separators.

Inspect your truck regularly – especially trailers, which run through the spray that the tractor kicks up.

Check brake condition often. Cracked brake linings are caused by rust, which has a greater volume than the iron it reacts with. The rust forces the linings away from the shoes. With linings riveted to the shoes, something has to give. The linings crack, a phenomenon called “rust jacking.”

Until the industry develops a protective coating that will keep salts off the trucks, the best way to combat corrosion from salt exposure is to keep your truck clean. LL