at what temp does salt not work

Salt for de-icing roads stops working well in normal winter use at about 15–20°F (around −9 to −6°C), and is considered basically ineffective below roughly 15°F (−9°C).

Quick Scoop

When people ask “at what temp does salt not work,” they usually mean road salt (sodium chloride) used to melt ice on streets and sidewalks. Pure salt brine can theoretically melt ice at much lower temperatures, but in real outdoor conditions it needs a thin film of liquid water, traffic movement, and time to do its job.

Key temperature points

• Around 32–25°F (0 to −4°C): Road salt works well with normal amounts; ice melts relatively quickly.

• Around 25–20°F (−4 to −7°C): It still works but more slowly, and you often need more salt to see the same effect.

• Around 20–15°F (−7 to −9°C): Melting becomes sluggish; salt needs longer contact and may leave surfaces partly icy.

• Below about 15°F (−9°C): Standard road salt is “practically” useless for de-icing; ice may not melt at all or will quickly refreeze.

Chemically, sodium chloride can depress the freezing point much lower in a controlled lab brine, but outside you rarely reach those ideal concentrations, so agencies treat 15–20°F as the practical cutoff.

What about other de-icers?

Other products keep working at lower temps:

• Calcium chloride: effective down to about −20°F (−29°C).
• Magnesium chloride: effective to around −13°F (−25°C).
• Treated or blended salts: can push the “working” range a bit below 15°F.

These are often used when the forecast says temps will stay well below 20°F so standard rock salt doesn’t just sit on the surface doing nothing.

Simple example

Imagine a parking lot at 28°F with a thin layer of ice: a light application of salt usually clears it in a short time. Drop that same lot to 10°F and use the same amount of salt; you’ll likely still be walking on ice because the salt can’t create enough brine or melt fast enough to matter.

Bottom line for everyday use: if the question is “at what temp does salt not work on roads?”, the practical answer is “below about 15°F, and it starts struggling once you get below about 20°F.”

Information gathered from public forums or data available on the internet and portrayed here.