Salt does not melt ice. Brine does.
The thing worth understanding is that rock salt has no effect on dry ice at all.
Salt works by dissolving into whatever thin film of liquid water is present and forming brine, which freezes at a lower temperature than water. That brine then undercuts the ice and breaks its bond with the pavement. No liquid water, no brine, no melting.
That is why salt thrown onto a cold, dry surface just sits there, and why it works far better once traffic has started to work it in.
Where the temperature floor comes from
Sodium chloride’s practical limit is around 15°F, and it starts losing usefulness well before that.
In theory it depresses the freezing point to about -6°F. In practice, on a real surface, the reaction slows so much by the mid teens that it stops doing anything useful inside the time you have. At 20°F it is sluggish. At 15°F it has effectively stopped.
In Western New York that is not an edge case. It is a normal January morning, several times a winter.
Adding more does not help
The instinct when salt is not working is to put down more of it. That is the wrong move on every count.
Below the working temperature, more salt melts no more ice — the chemistry is not rate-limited by how much is on the ground. What extra salt does do is run off into the soil, kill the grass along the edge of the drive, corrode concrete and metal, and cost money.
That brown strip along the driveway every April is almost never winter kill. It is salt.
- More salt below 15°F melts no more ice
- Excess runs off and damages turf, concrete and vehicles
- Salt on turf is the usual cause of the dead spring edge
- Pre-treating before the storm beats over-applying after it
What actually works when it is properly cold
Below the rock salt threshold the answer is a different chemical, not more of the same one.
Calcium chloride works down to about -25°F and releases heat as it dissolves, which helps it get started in conditions where sodium chloride cannot. Magnesium chloride is gentler on planting and concrete and works to roughly 0°F. Both cost more per bag, and both are applied at lower rates, which narrows the gap.
The other tool is timing. Anti-icing — treating before the snow arrives — stops the bond forming in the first place and uses far less material than breaking a bond after the fact. See salting and ice management.
Sand is traction, not melting
When it is too cold for any deicer to work, the answer is to stop trying to melt the ice and start trying to walk on it.
Sand does nothing chemically. It sits on top and gives boots and tyres something to grip, which in a deep cold snap is the only thing that helps. It is also the honest option when a surface simply cannot be cleared — a north-facing walk in shade at 5°F is not going to melt, whatever is thrown at it.
The trade-off is that it all has to be swept up afterwards, and anything that washes into beds and drains has to come out of there too. That cleanup is part of the spring bill whether or not anyone mentions it in November.
What to ask your contractor
This is a question worth putting to anyone quoting a winter contract.
Ask what they use when the temperature drops below fifteen, and whether it costs extra. A contractor who has not thought about it will say ‘salt’ and mean it. That answer is fine for December and useless in a cold snap, which is exactly when a lot becomes dangerous.
Refreeze is the related question. A lot cleared at six that melts at noon can be an ice rink by five, and whether anyone returns for that should be in the contract rather than assumed.