If you live in a cold climate, you may have noticed concrete slabs mysteriously shifting, cracking, or even lifting during the winter. This phenomenon, known as "winter heaving", can wreak havoc on driveways, sidewalks, patios, and other concrete surfaces. While frustrating, it's a natural process caused by freezing temperatures and moisture beneath the slab. Unfortunately, because heaving is a natural occurrence, most concrete companies won’t warranty slabs against cracking due to frost heave. Let’s dive into why this happens and what you can do about it.
What is Winter Heaving?
Winter heaving occurs when moisture in the ground freezes, expands, and pushes the concrete upward. Since frozen water can expand by nearly 9% in volume, this creates an immense amount of pressure beneath the slab. The result? Your once-level concrete starts shifting, cracking, or even forming hazardous bumps.
This process happens in cycles—each time the ground freezes and thaws, the concrete moves. Over time, these repeated shifts weaken the structure, leading to visible damage.
Why Does Heaving Cause Concrete to Crack?
Concrete is strong but not particularly flexible. When pressure builds up from beneath due to frozen soil, the slab can only resist so much before it fractures or lifts unevenly. Once a crack forms, water can seep in, freeze, and make the problem even worse.
Because winter heaving is a natural soil movement issue rather than a flaw in materials or workmanship, most concrete companies do not offer warranties against cracking from frost heave. It’s simply beyond their control. That being said, you are not left without options for this.
Solutions for Heaved Concrete:
If your concrete has already heaved, you have a few options depending on the severity of the damage:
Wait until Spring: While I would never suggest waiting to eliminate a dangerous tripping hazard, sometimes that is all you can do. If this is the first time you have noticed the concrete heaving, it may settle back to original position in the spring and is best left untouched until the ground thaws and you can determine what the next steps should be.
Poly-jacking: If the slabs don't return to proper heights you can have a poly jacking company lift the abutting slabs to match the heaved ones. This will eliminate those tripping areas. This will also create a moisture barrier beneath the concrete and help stabilize the slabs to avoid future issues.
Concrete grinding: If one slab lifted and the rest did not, you can grind off the high spots leaving the transitions smooth. This should be a last resort and can only be done if the amount to be ground does not exceed 25% of the thickness. I'd also recommend sealing the concrete after grinding it to protect the surface.
Crack Sealing: If the winter heave has caused your concrete to crack, you can use a concrete joint or crack sealant to close the cracks and keep the water out. Different sealers can be used depending on the type of concrete and it's location.
Preventing the concrete from heaving:
Water can be the biggest enemy of concrete and proper drainage should be a focal point of every home and business owner. If water does not properly drain under your concrete it can cause erosion and settling. During the cold winter months, the water can freeze, expand, and heave your concrete. Installing drains and proper downspouts to direct the water as far away from structures and concrete is your best defense for water damage. Sometimes things are out of our control but luckily, there are excellent options for repairing your uneven or broken concrete.
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