The answer first
On concrete pavers, brick and mortar joints, buy plain rock salt — sodium chloride — and use as little of it as you can. That is not the cheap answer dressed up; it is what the industry body for interlocking concrete pavement publishes. Its guidance says rock salt “is the least damaging to concrete materials and should be used whenever possible,” tells you to “consider the judicial use of calcium chloride” when you need something faster, and states that “the use of magnesium chloride or CMA is not recommended because they can chemically degrade all types of concrete.”
On a composite deck, Trex names the chemistry itself: “Calcium chloride or rock salt, available in many home centers, will melt ice on Trex decking,” followed by “rinse off when first practical.” The thing Trex prohibits is not a chemical at all — it is a metal shovel.
On a roof, no bag is the answer. Throwing ice melt up there is how the chloride ends up in gutters, on siding, in planting beds and down the driveway. The published fix for roof ice is a heat cable, and that is a different purchase.
And the part that makes this site disagree with its own sources: every one of those recommendations is optimizing for the surface. We are also optimizing for the car you park next to it. Chlorides are what get walked into the garage and splashed onto an underbody, and rock salt is the cheapest, most mobile chloride there is. Where the treated surface drains toward where you park, the published surface advice and the right answer for your car pull in opposite directions. The rest of this page is about choosing deliberately rather than by accident.
How we judged this
1. What the surface maker publishes. A paver manufacturer, a decking manufacturer and a roofing manufacturer all have warranties to protect, so their published de-icing guidance is the most specific you will find. It beats the front of any bag.
2. What the chemistry does in deep cold. Sodium chloride is the weakest of the common chemistries once it gets genuinely cold, so “least damaging” and “works tonight” are not always the same bag.
3. Where the runoff goes. This is the question that is missing from every other page on this topic. A paver path that drains into a planting bed is a different decision from an apron that drains under your front wheels.
4. Published coverage, where it exists. A product spread at half the rate is not twice the price, and over-application is the single most common mistake on every surface here.
Pavers and brick: the published guidance is sodium chloride
Concrete pavers are not a poured slab. They are dry-cast units made to a density and absorption specification, laid on sand with sand-filled joints, and the joints are usually what fails first. The relevant published standards are ASTM C936, which carries freeze-thaw durability criteria for paving units, and ASTM C1645, the test method it references for freeze-thaw and de-icing salt durability. A unit that meets those is already engineered against this problem.
What the published guidance adds is a ranking between chemistries, and it is the opposite of the shelf hierarchy. Rock salt is named as least damaging. Calcium chloride is allowed, with a caution to be judicious. Magnesium chloride and calcium magnesium acetate — the two that get sold as the gentle, premium, pet-and-plant-friendly options — are not recommended, on the stated grounds that they can chemically degrade all types of concrete.
That matters here because our own concrete page ranks a CMA blend highly, and we are not quietly walking that back. The two recommendations are answering different questions. On a poured, cured, well-finished driveway slab, the mechanism that does the damage is freeze-thaw cycling driven by liquid water in the pores, and keeping chloride off your car matters more than the marginal difference between chemistries. On dry-cast pavers with sand joints and mortar nearby, the industry body is pointing at a chemical degradation path and naming the products it does not want on them. Same site, different surface, different answer — and you should know which surface you have.
Published de-icing guidance, by surface| Surface | What the maker or industry body publishes | What that means in a bag |
|---|
| Concrete pavers, brick, mortar joints | Rock salt is "the least damaging to concrete materials and should be used whenever possible"; calcium chloride judiciously; magnesium chloride and CMA "not recommended" | Plain sodium chloride, spread thin |
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| Composite decking (Trex) | "Calcium chloride or rock salt ... will melt ice on Trex decking"; "rinse off when first practical"; plastic shovel only | Either of the two cheap chlorides, then a hose |
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| Poured concrete driveway slab | Calcium chloride stated for concrete at least one year old, properly designed, constructed and cured | Chloride-free if it drains toward the car; otherwise calcium chloride, sparingly |
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| Asphalt | No chemistry restriction published by the chemistry makers; the failure mode is softening and binder damage from heat and water, not salt attack | Any of them, thin - the risk is the shovel and the plow blade |
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| Roof and gutters | No bagged product is published for roof use by any maker on this page | A heat cable, not a bag |
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Composite decking: the chemistry is fine, the shovel is not
This is the surface people are most nervous about and the one with the clearest published answer. Trex publishes, for its early-generation boards, that “calcium chloride or rock salt, available in many home centers, will melt ice on Trex decking,” and to “rinse off when first practical.” For the Transcend, Enhance and Select lines it publishes the same thing: “use calcium chloride or rock salt to melt the snow and ice from the deck surface,” and “a plastic shovel may be used to remove snow from composite decking.”
The prohibition is mechanical. Trex publishes “NEVER use a metal snow shovel on Trex decking” and warns that “a shovel may scratch the deck, which is not covered under warranty.” So the thing that will actually cost you money on a composite deck this winter is the aluminum scoop in the garage, not the bag.
The rinse instruction is the part people skip, and it is doing real work. Chloride left on the surface after the ice has gone has nothing left to melt and plenty of time to sit in the board grain and the gaps. Rinsing when it is practical — which in February means the first mild day, not the same afternoon — is the whole maintenance routine.
Why the cheap bag is also the one you use most of
Sodium chloride is the weakest common chemistry in deep cold, and that has a cost that is not on the price tag. Calcium chloride is published by OxyChem as effective to −25 F. The CMA blend on our concrete page is published to −10 F. The rock salt bag here publishes no working temperature at all, which is itself the answer: plain salt gives up first, and when it stops working people respond by putting more down.
So the arithmetic that matters is not dollars per pound, it is pounds per winter. A bag that works at the temperature you actually get gets spread once. A bag that does not gets spread three times, and all three applications end up in the same places — the joints, the planting bed, and the tread of your boots.
That is ours, not a maker’s claim, and it is the reason the paver guidance pairs “use sodium chloride” with “do not over apply deicing chemicals; follow the recommended dosage” in the same breath. The published advice is both halves or neither.
Asphalt, gravel and the surfaces nobody publishes for
Asphalt gets asked about constantly and has the least published guidance, because chlorides are not really its failure mode. Asphalt is a flexible pavement held together by bitumen; what hurts it is water getting into cracks and freezing, and heat softening the binder. The de-icer is not attacking the material the way it can attack cement paste.
The practical risks on asphalt are mechanical and seasonal: a plow blade or a metal shovel on a soft or patched surface, and water sitting in cracks you have now kept liquid for longer. If you have asphalt, spend the effort on sealing the cracks in the fall rather than on choosing an exotic bag.
Gravel is simpler still: nothing to protect, so use whatever clears safely and least of it. A thin spread for grip beats a melt you cannot drain anywhere.
Skip this
Do not put a bag of anything on your roof
Ice dams produce the single most common version of this question, and a bagged de-icer is the wrong tool for it. Everything you throw up there comes down — over the shingles, into the gutter, onto the siding, through the downspout and across whatever the downspout drains onto, which is very often the driveway you park on.
An ice dam is a heat-loss and ventilation problem wearing an ice costume, and the hardware answer is a heat cable laid in the gutter and up the lower courses, on a thermostat so it is not running in March. We work the published rules for those, including the temperature and the circuit requirements, on the heat cable page — the same hardware, the same rules, a different run.
If the ice on your roof is already a structural worry, that is a roofer, not a product decision.
The runoff question, which decides it for most people here
Everything above is the surface’s point of view. Here is yours.
Salt does not stay where you spread it. It dissolves, it runs downhill, and it gets carried indoors on footwear and tires. The path from a treated paver walk to the underside of your car is short: brine on the slab, brine on the tread, brine in the footwell carpet and brine on the seams and the subframe. That is the mechanism the whole road-salt page is about, and it does not care whether the chloride came from a county truck or from your own bag.
So the decision is really about slope. If the surface you are treating drains away from where you park and away from the garage door, take the published surface advice and buy rock salt. If it drains toward either, buy the chloride-free product and accept that it costs more and works less hard. Safe Paw publishes a salt-free, chlorine-free, acetate-free formula, a coverage rate of two cups per 150 square feet, and that it “lasts 72 hours on the surface” — and the only surface it explicitly claims is cured concrete, which is worth knowing before you put it on anything else.
There is a third move that costs nothing: treat less area. Most people salt a whole driveway when what they need is a clear path to the door and a clear strip where they put their feet getting out of the car. A containment mat inside the door catches what still gets through, which is the cheapest half of this whole problem.
What we would buy
Paver or brick path, draining to a lawn or a bed: plain rock salt, spread thin, with the published dosage respected rather than eyeballed. It is the cheapest bag and the one the paver industry body actually names.
Anything draining toward the car or the garage door: the chloride-free product, and less of it. You are paying a premium to keep a chloride out of your wheel arches, and on a $30-versus-$300 basis that is the same trade this whole site is built on.
Composite deck, and it gets properly cold: calcium chloride, because Trex names it and it still works when salt has stopped. Then the plastic shovel, then the rinse.
Roof or gutter ice: a heat cable on a thermostat, and nothing from a bag.
