What rock salt actually does to your driveway
Salt doesn't eat concrete the way most people think. What it does is harder on the surface, and it's a big reason so many Omaha driveways look sandblasted by March.
It's not the salt, exactly
Plain rock salt doesn't really dissolve concrete. What it does is melt ice at temperatures where it would've stayed frozen. So now there's water sitting on the slab and soaking into the top of it, and when the sun goes down, it freezes again.
Water grows by about nine percent when it freezes. If it's soaked into the surface, it pushes from the inside. Do that over and over and the top layer starts popping off in flakes. Contractors call that scaling, and once it starts, every winter makes it worse.
A Nebraska winter already puts a driveway through somewhere north of a hundred freeze-thaw cycles. Salt adds a bunch more.
New concrete is the most at risk
If your driveway, walk or patio was poured this year, don't put any de-icer on it this winter. None. Concrete keeps gaining strength for weeks after it's poured, and it isn't ready for salt and repeated freezing until it's been through a full season. Use sand for traction instead.
That includes the salt the city puts down on the street. It rides home on your tires and drips onto the driveway all winter. On a warm day, hosing off the spot where you park helps more than you'd think.
What to use, and what to skip
- Skip anything with ammonium nitrate or ammonium sulfate in it. Those actually attack concrete. Read the bag.
- Rock salt is cheap and works down to about 15 degrees. Go easy with it, and never on concrete less than a year old.
- Calcium chloride works when it's much colder, so you need less of it. Still use it sparingly.
- Calcium magnesium acetate (CMA) is the gentlest. It costs more and works a little slower.
- Sand doesn't melt anything, and that's the point. You get grip without another freeze-thaw cycle.
The best thing you can do is shovel early, before cars and feet pack the snow down into ice. Then you barely need any of the stuff above.
Seal it every few years
A penetrating sealer soaks into the surface and keeps water and salt from getting in. Look for silane or siloxane on the label. It needs to be above 50 degrees and dry when it goes on, which around here means September or early October, or else waiting for spring. Reapply every three to five years.
Skip the glossy acrylic sealers on a driveway. They look great for about a year and then start peeling where you drive.
If your driveway is already flaking
Light scaling on a slab that's otherwise flat and solid can often be fixed with a resurfacing overlay, for a lot less than replacing it. If it's flaking and also cracked through and sinking, an overlay won't hold up. Call (531) 236-6623 and describe what you're seeing, or have us come take a look, and we'll tell you which one you've got.