Rock Salt vs Calcium Chloride vs Magnesium Chloride: Which Ice Melt to Buy

Rock salt, calcium chloride, magnesium chloride and CMA all melt ice, but they do it differently. They also stop working at very different temperatures and treat your concrete, pavers, plants and pets very differently. Picking the wrong one is how people end up with a walkway that is still icy at 6 AM, or a paver patio that looks pitted by spring.

This guide compares the four ice melt types we carry side by side. It covers how cold each one works, what each is good at, and where each one does not belong. Every figure comes from the product listings and manufacturer data for the ice melts on our shelves.

Rock salt vs calcium chloride vs magnesium chloride vs CMA at a glance

Type	How cold it works	Best at	Watch out for
Rock salt (sodium chloride)	Works well to about 20°F, then slows badly	Usually the lowest cost chemistry, large driveways and lots	Harshest on concrete, metal and planting; sodium builds up in soil
Calcium chloride	To -25°F	Deep cold, fast melting, drilling through thick ice	Not recommended on masonry, stone or wood; easy to over apply
Magnesium chloride	To about -15°F	A middle ground: colder than salt, gentler than calcium chloride	Draws moisture from the air, so keep the pail sealed
CMA (calcium magnesium acetate)	To -25°F	Pavers, natural stone, pets and planting beds	Costs more per pound than the chlorides

Rock salt: usually the cheapest way to clear a driveway

Rock salt is sodium chloride. It has been the default deicer for a century because, as a chemistry, it is usually the least expensive per pound. Check prices before you buy, though: some blends, such as Snow Shield, can come in lower per pound in our store. The catch is temperature. Sodium chloride melts well down to about 20°F and then stalls, so on a single digit night it is doing little more than adding grit.

It is also the most aggressive common deicer. It is hard on concrete that has not fully cured, on metal railings and car panels, and on lawn edges and planting beds, where sodium accumulates in the soil.

Where it fits: long driveways, parking areas and anywhere cost per pound matters most. Our options are EveryMan's Rock Salt in 25 and 50 lb bags, the Rock Salt Ice Melt Pail in 8, 20 and 45 lb sizes, and Halite Crystals, a graded rock salt in a resealable pail.

Where it does not fit: decorative pavers, natural stone, new concrete and dog routes.

Calcium chloride: the coldest working ice melt

Calcium chloride is the only common deicer that keeps working at -25°F. It attacks ice two ways. It drops the freezing point far lower than salt does, and it is exothermic: it releases heat as it dissolves, so it melts downward instead of waiting for sun.

It comes in two forms:

• Pellets, like Peladow Premier. OxyChem makes them round so they bore down through ice and break the bond with the pavement quickly. OxyChem rates Peladow to melt up to three times faster than competing materials. Our Calcium Chloride Pellets Pail is another pellet option, in pails from 8 to 40 lb.
• Flake, like DOWFLAKE Xtra at 83 to 87 percent calcium chloride. Flake has more surface area, so it starts dissolving sooner.

Calcium chloride goes further than rock salt, so spread it thin. OxyChem's rate for Peladow is 28 lb per 1,000 sq ft (about 4 oz per square yard), which works out to roughly 1,800 sq ft per 50 lb bag.

Important for hardscape: OxyChem does not recommend calcium chloride on masonry or stone, or on wood decking, steps and thresholds. Read that before you salt a bluestone walkway. For smaller jobs, the Calcium Chloride Pellets Pail comes in a 40 lb pail.

Magnesium chloride: the middle ground

Magnesium chloride works colder than rock salt, to about -15°F on the products we carry. It is also markedly gentler on paws, concrete and planting than sodium or calcium chloride, and it costs less than the acetate products.

• Dead Sea Magnesium Chloride comes in 50 lb bags, as pellets or flake, and is rated to -15°F.
• Magnesium Chloride Flakes come in an 8 lb pail. Flakes start melting on contact, but work through faster, so expect to reapply in a long storm.

Tip: magnesium chloride pulls moisture from the air and will cake if the container is left open. Reseal the pail between storms.

CMA: the gentlest option for pavers and pets

CMA is calcium magnesium acetate. It is an acetate, not a chloride, and it works partly by stopping ice particles from bonding to each other and to the pavement. That gentler mechanism is why it costs more per pound, and why it is the product to use where surface damage matters. The CMA pails we carry are listed as suitable for properly cured concrete, asphalt, pavers and masonry at least 12 months old.

• Pink Penguin, Green Seal and Blue Arctic Fox are the CMA pails we carry.
• All three come in 8, 20 and 45 lb resealable pails. Their colored granules show where you have already spread.

What about blends?

Some ice melts mix chemistries to balance cost, cold and gentleness:

• Safe Step Enviro-Blend 6300 blends sodium, magnesium and potassium chlorides with MG 104, a melting catalyst that helps prevent refreezing. It works to -10°F.
• MeltMaxx blends calcium chloride and rock salt in an 8 lb pail.

Blends usually cost less than straight calcium chloride and work colder than straight salt.

How to choose: three questions

1. How cold does it get where you are? If nights regularly drop below zero, you need calcium chloride or a CMA product rated to -25°F. For most storms that happen in the 20s, rock salt or a blend will do the job.
2. What surface are you treating? For pavers, natural stone and decorative concrete, use CMA or magnesium chloride. Keep calcium chloride off masonry and stone. Keep every deicer off concrete less than a year old.
3. Who walks on it? On a daily dog route, pick a CMA product and wipe paws after walks. Pet friendly means less irritating, not harmless.

Common mistakes

• Over applying. More product does not melt faster. It wastes money and is harder on surfaces.
• Salting before shoveling. Clear loose snow first so the granules reach the bonded ice underneath.
• Leaving containers open. Chloride deicers draw moisture and turn to a solid block.
• Using rock salt in deep cold. Below about 20°F it slows badly. Keep a pail of calcium chloride for those nights.

Frequently asked questions

What is the best ice melt for very cold temperatures?

Calcium chloride. It is the only common deicer that keeps working at -25°F, and it releases heat as it dissolves. Peladow Premier and DOWFLAKE Xtra are both calcium chloride.

What ice melt is safest for pavers and natural stone?

CMA (calcium magnesium acetate) is the usual pick. The CMA pails we carry are listed as suitable for properly cured concrete, asphalt, pavers and masonry at least 12 months old. Magnesium chloride is the next gentlest. OxyChem does not recommend calcium chloride on masonry or stone.

At what temperature does rock salt stop working?

Sodium chloride melts well down to about 20°F and then slows badly. Below that, switch to calcium chloride, magnesium chloride or a CMA product.

Is magnesium chloride better than calcium chloride?

It depends on the job. Calcium chloride works colder, to -25°F. Magnesium chloride works to about -15°F but is gentler on paws, concrete and planting.

Can I use ice melt on new concrete?

No. Concrete less than 12 months old has not cured enough for any deicer. Use sand or a stone dust traction grit like Glacier Grip instead.