How do I keep concrete from cracking in winter?

Winter damage to concrete starts with water. The Federal Highway Administration (FHWA) explains that chemical deicers amplify the freeze-thaw damage concrete already suffers, partly because salt solutions leave it more saturated.^[1] So the plan is simple: keep water out of the slab, let it drain off, and use as little deicer as you can, of the right kind.

Before the first freeze

Seal cracks and joints. An open crack fills with water and grit, and both make it worse each winter. A flexible polymer sealant such as Quikrete's Advanced Polymer Concrete Crack Sealant is made for sealing horizontal or vertical control joints and expansion joints in sidewalks and driveways,^[7] and should not be applied below 40 F or to frozen surfaces.^[7] A pourable crack seal is another option for narrow cracks; Quikrete's is applied between 45 and 100 F and kept from freezing.^[8] Do it on a dry fall day, before nights start to freeze. How to fix cracks in a concrete driveway covers the prep.

Seal the surface. A penetrating water repellent keeps water and salt out of sound concrete. Euclid describes its Baracade Silane 40 WB as a breathable water repellent that protects concrete against water intrusion, deicing chemicals and freeze-thaw exposure.^[3] Timing matters: its data sheet says to cure new concrete a minimum of 7 days, and that the surface must be clean and dry, drying a minimum of 24 hours after rain.^[3] Follow the sealer's own label for coverage and recoating.

Make sure water drains off. Quikrete says a driveway should be sloped slightly toward the street, with 1/4 inch per running foot sufficient.^[5] FHWA's advice for avoiding freeze-thaw damage at joints is to reduce the ingress of water-salt solutions into joints and quickly drain them away.^[1] Point downspouts away from walks and driveways, fill low ground along the edges so meltwater does not sit against the slab, and clear leaves out of joints.

During the winter

Shovel first. The less snow is left to melt, the less deicer you need and the less water soaks into the slab. Clear walks soon after snow stops, before foot traffic packs it into ice.

Pick and use deicer carefully. FHWA reports that calcium chloride, including the calcium chloride that forms when magnesium chloride deicers react in the concrete, can cause a highly expansive reaction that damages the cement paste.^[1] Read the label, spread a thin layer only where people walk, and let sand handle the rest.

Rinse off road salt. Cars carry salt and road treatments onto the driveway. On a mild afternoon after a storm, hose it off the driveway and garage slab.

A Virginia rule on deicer sales. A section in the Fertilizer chapter of the Code of Virginia makes it "unlawful for any person to offer for sale any deicing agent containing urea or other forms of nitrogen or phosphorus intended for application to parking lots, roadways, and sidewalks or other paved surfaces in the Commonwealth."^[6]

New concrete needs extra care

Concrete poured this year is especially vulnerable. The Town of Berryville tells residents that concrete takes approximately a year to cure and is highly susceptible to chemical damage, especially from deicers, during that time, and asks them to avoid salt and other deicers on it for about a year.^[2] It lists sand, sawdust, clean kitty litter and birdseed as less damaging options that improve traction.^[2] If you have a new driveway, ask your contractor how it was cured; how long new concrete takes to cure explains the first weeks.

Pouring or patching close to winter

Fresh concrete and fresh patches are at their weakest. Quikrete tells users to protect concrete from freezing during the first 48 hours, with plastic sheeting and insulation blankets if temperatures are expected to fall below 32 F.^[4] Patching products have their own limits: Quikrete's Re-Cap resurfacer calls for air and concrete between 50 and 90 F, and for plastic sheeting and insulation blankets if temperatures are expected to fall below 32 F.^[9] If a repair can wait until spring, it usually should.

Stop and call a pro if

• A slab has heaved, sunk or tilted over the winter, or a step has pulled away from the house.
• The surface is flaking away in sheets or getting worse each year; see why concrete spalls.
• You see rust stains or exposed steel.
• Water is getting into the basement or garage where a slab meets the house.
• A crack is wider than a sealant is made for, or one side sits higher than the other.

Getting help in Virginia

Loclis lists DPOR-licensed concrete businesses with their licence number and class. Look up concrete contractors in Blacksburg, browse concrete repair or sealing and resurfacing, or see all concrete and hardscaping answers. If the damage is already done, whether to repair or replace cracked concrete helps you decide what to ask for.

Describe the job once and licensed local concrete businesses quote the repair or the sealing.