Rock salt stops working around −10 °C. Applying more of it below that temperature costs money, damages concrete and does not melt anything.
What we use and when
We match the product to the pavement temperature: brine pre-treatment ahead of a freezing-rain event, treated salt in the normal range, and a calcium or magnesium blend when it gets cold enough that plain salt is useless.
Liability records
Commercial clients and condominium corporations get application records with product, quantity, time and surface temperature — the documentation a slip-and-fall claim asks for.