How Frost Heave Actually Works
I always thought frost heave was simple: water freezes, expands, pushes stuff up. But it's more complicated than that.
The Ice Lens Thing
Rick explained this over coffee one winter morning. The worst frost heave doesn't come from water in the soil freezing in place. It comes from water migrating toward the freezing front and forming layers of almost pure ice.
As the ground freezes from the top down, it creates a suction that draws water up from deeper soil. That water freezes into horizontal ice layers called ice lenses. These lenses can get pretty thick. An inch. Several inches. And they lift everything above them.
That's why frost heave can be way more than the 9% expansion you'd expect from water freezing. The ice keeps building as long as water keeps migrating to the freezing zone.
Soil Type Matters
Not all soils heave equally. My neighbor Helen has a newer house with engineered backfill around the foundation. Gravel and sand. Minimal frost heave problems because those soils drain too fast for ice lenses to form.
My backfill is whatever native soil was there in 1978. Silty stuff that's perfect for ice lens formation. Water moves through it just fast enough to feed the freezing front but not fast enough to drain away. The worst of both worlds.
Frost Depth in Our Area
The frost line where I live is about 4 feet. That means the ground can freeze that deep in a typical winter. My footings are just below that, at about 4.5 feet. They're supposed to be safe from direct frost heave.
But the soil against my foundation walls? That freezes every winter. And frozen soil expands and pushes horizontally against the concrete. The footings might be below the frost line, but the walls are still fighting frost pressure.
Frost Damage I've Found
After learning about frost heave, I started recognizing the damage on my own house.
The Surface Spalling
The part of my foundation that's exposed above grade looks rough. Pitted. Areas where the surface has flaked off. That's freeze-thaw damage to the concrete itself.
Water gets into the tiny pores in concrete. It freezes. Expands. Pops off a thin layer. Year after year, the damage accumulates. My foundation has been doing this for 45 winters. The exposed part looks 45 years older than the buried part.
The North Wall Crack
I have a horizontal crack on my north wall that's been stable for as long as I've owned the house. The structural engineer I hired said it was likely from a combination of frost pressure and hydrostatic pressure acting together over many years.
The north side of the house is shaded. Snow piles up there. The soil stays frozen longer than on the sunny south side. That wall has fought more frost cycles than any other. Makes sense that it shows more damage.
The Garage Floor
My garage floor has heaved in one spot near the door. About half an inch higher than the surrounding floor. That's actual frost heave under the slab.
Garage floors aren't protected like house foundations. No basement to keep them warm. The ground under my garage freezes every winter. When ice lenses form under a thin concrete slab, the slab lifts. Mine has.
The Front Steps
My concrete front steps have pulled away from the house by about an inch. They also tilt slightly away. Classic frost heave damage. The steps are on their own shallow footing, way above the frost line. They move with the freezing soil every year. The house doesn't.
Eventually I'll replace them with steps on a deeper footing. For now, I just caulk the gap every spring.
How Frost Heave Gets Worse Over Time
The frustrating thing about frost damage is that it accumulates. Each cycle adds a little more.
Adfreezing
This is a term I learned from Rick. When soil freezes against a foundation wall, it literally bonds to the concrete. As the soil heaves upward, it tries to drag the wall with it. Each winter, a little uplift stress. Each spring, the bond releases.
Over decades, this cycling can fatigue the concrete. Connections weaken. Cracks develop. Nothing dramatic in any single year, but the sum of 45 years is significant.
Crack Propagation
Any crack in concrete is an invitation for water. Water gets in, freezes, expands, widens the crack. Next year, more water fits in the wider crack. More expansion. Wider still.
I have cracks that started as hairlines and are now 1/8 inch wide. They didn't get there in one winter. They got there one freeze-thaw cycle at a time over many years.
Settlement After Thaw
When ice lenses melt, they leave voids. The soil structure that was lifted up doesn't always settle back evenly. Over many cycles, you can get progressive settling in some areas and persistent heave in others.
My porch foundation shows this. One side has heaved and stayed up. The other side has settled. The difference has accumulated over decades. Now the porch slopes noticeably.
What I Do to Minimize Frost Damage
I can't stop winter from happening, but I can reduce the impact on my foundation.
Seal Cracks Before Winter
Every fall, I check my foundation for cracks and seal any that could let water in. Concrete caulk for the surface. Hydraulic cement for larger gaps. The goal is to keep water from getting into the concrete where it can freeze and cause damage.
An afternoon of sealing potentially saves years of progressive damage. It's the best return on investment I know of for foundation maintenance.
Keep Snow Away from the Foundation
Snow piled against the foundation melts slowly and refreezes repeatedly. It extends the frost season for that soil. I try to keep snow cleared away from the foundation, especially on the north side where it accumulates.
This is easier said than done. Some winters we get 4 feet of snow. I can't clear it all. But I make an effort.
Drainage for Spring Thaw
When all that snow melts in spring, the water has to go somewhere. Good drainage means it goes away from the foundation instead of soaking into the soil against the walls.
I check my grading every spring. Make sure nothing has settled that would direct snowmelt toward the house. A few wheelbarrows of topsoil can prevent a lot of problems.
Consider Exterior Insulation
Rick mentioned that some people install rigid foam insulation against the foundation to keep the soil warmer. Less frost penetration means less frost heave. I haven't done this, but if I ever excavate for other reasons, I'd consider adding it.
My neighbor Helen's newer house has this. She doesn't have the frost pressure problems I do.
Repairing Frost Damage
Some damage is cosmetic and some is structural. I've dealt with both.
Surface Repair
The spalling on my exposed foundation bothers me more for appearance than structure. I've patched the worst spots with polymer-modified repair mortar. It's held up for about five years so far.
The key is proper prep. Remove all loose material. Use a bonding agent. Apply the patch thick enough to be durable. Thin patches just flake off again.
Crack Injection
The horizontal crack on my north wall was leaking. I had it injected with polyurethane. Cost $350. It sealed the crack and created a flexible bond that can accommodate some seasonal movement without cracking again.
Epoxy injection is stronger but rigid. For cracks in a wall that's still experiencing frost cycles, flexible polyurethane makes more sense to me.
Steps and Porches
Eventually I'll bite the bullet and replace my front steps and porch with properly engineered construction. Deep footings. Frost-protected design. Probably $4,000-6,000 when I do it.
For now, I'm just monitoring and maintaining. Caulking gaps. Keeping water away. Buying time until I can do it right.