Why the Apron Sinks and the Garage Floor Does Not
The slab between your garage floor and your driveway is called the apron, and it sinks because it was never sitting on solid ground to begin with. When your house was built, the soil around the foundation was dug out and shoveled back in, and that backfill never reaches the density of the undisturbed ground it replaced. Over the years it compacts and washes out, the apron drops with it, and the garage floor stays exactly where it is. That step you are stepping over is the difference.
- A sunken driveway apron is a soil problem, not a concrete problem -- the slab itself is usually in fine shape.
- Polyurethane foam lifting brings the apron back to grade in about two hours, and you can park on it the same day.
- Lifting an apron typically costs 25 to 50 percent of what replacing that section costs, usually in the $1,200 to $3,000 range in the Twin Cities.
The Apron Is the Slab Between Your Garage Floor and Your Driveway
It is a short section, usually four to eight feet deep, running the full width of the garage opening. Most homeowners never think about it as a separate piece of concrete until it drops and creates a lip at the door.
That lip is the first thing people notice. The second is the gap under the closed garage door, where the rubber seal no longer touches anything. Then come the leaves, the melting snow, and the mice.
Why the Apron Sinks and the Garage Floor Does Not
The garage floor and the apron are supported by two completely different things.
Your garage floor sits inside the foundation walls, on ground that was never excavated. The apron sits outside them, on backfill -- the loose soil pushed back into the trench after the foundation was poured. Backfill settles for years. Undisturbed ground does not. The two slabs were never going to stay level with each other, because only one of them was built on solid ground.
Water accelerates it. Roof runoff, downspouts, and snowmelt all concentrate right at the garage opening, and moving water carries fine soil particles out from under the slab. What is left behind is a void -- an empty pocket between the bottom of the concrete and the dirt. Once the void opens up, the slab has nothing holding its weight and it drops.
Here is the part that surprises people: once the apron tilts back toward the garage, every rainstorm makes it worse. Water that used to run down the driveway now runs into the joint at the garage door, straight into the void, washing out more soil. The problem feeds itself.
Why Minnesota Winters Make the Gap Grow Faster
Frost regularly drives three to four feet deep in the Minneapolis metro. Water in the soil under and around the apron freezes, expands, and lifts the slab slightly. In spring it thaws, the soil consolidates, and the slab drops back down -- but not always to the same place it started.
Repeat that cycle dozens of times a winter and every void under the apron gets a little bigger. This is why an apron that was barely noticeable in October is a genuine trip hazard by May. Minnesota's freeze-thaw cycle does not create the problem, but it runs the clock about twice as fast as it would in a milder climate.
How to Tell Your Apron Is Settling Before Water Starts Getting In
Most homeowners wait for the gap under the door. There are earlier signs:
- Daylight visible under the closed garage door at one end but not the other
- Water pooling at the garage door instead of running down the driveway
- A visible step or lip where the apron meets the garage floor
- The joint at the garage opening widening or filling with debris
- Rainwater staining or a damp line just inside the garage door
- Salt and de-icer residue collecting at the low corner
If you can slide a pencil into the joint at the garage door, the slab has already moved.
Can a Sunken Apron Be Lifted Instead of Replaced?
In most cases, yes. If the concrete is structurally sound -- meaning it has not broken into multiple loose pieces and the surface is not crumbling -- it can be lifted back to grade rather than torn out.
The method is polyurethane foam injection, sometimes called polyjacking. High-density foam is injected through holes about the size of a dime, expands to fill the void completely, and cures hard within about 15 minutes. This is the same process used on garage aprons and full concrete driveways across the metro.
Polyurethane foam does not absorb water, compress, or wash away -- which means the same freeze-thaw cycle that opened the void in the first place has no effect on the repair material. The foam also weighs roughly 2 to 4 pounds per cubic foot, so it fills the void without adding new load to soil that is already marginal.
Lifting is the wrong call in a few situations. If the apron has broken into three or four loose sections that move independently, if the surface is spalling badly and flaking apart, or if the slab is so thin that it cannot carry a lift, replacement is the honest recommendation. A contractor should be willing to tell you that.
What Lifting a Driveway Apron Looks Like
The process is short and there is almost nothing to clean up afterward.
- The crew drills a series of ports through the slab, each one roughly the size of a dime.
- Foam is injected through the ports. It expands beneath the concrete, filling the void first and then beginning to lift.
- The lift is monitored in real time with a level, and injection is adjusted port by port until the apron sits flush with the garage floor and drains away from the house.
- The ports are patched with cement grout.
- The joint at the garage opening is sealed so water stops running into the space below.
Total time on a typical apron is about two hours. There is no excavation, no slurry, no wheelbarrows across your lawn, and no curing period to wait out. You can drive on it the same day.
Lifting Versus Replacing the Apron
| Lifting With Polyurethane Foam | Replacing the Apron | |
|---|---|---|
| Typical cost | $1,200 to $3,000 | Two to four times the cost of lifting |
| Time on site | About two hours | One to two days, plus prep |
| Time to drive on it | Same day | Seven days minimum |
| Disruption | Dime-sized holes, patched | Demolition, hauling, forms, new pour |
| Color match | Keeps your existing concrete | New slab will not match the rest of the driveway |
| The void underneath | Filled completely | Filled only if the crew compacts the base properly |
That last row matters more than most homeowners realize. Replacing the slab without addressing the void and the drainage means the new concrete sits on the same unstable soil the old one did.
What to Fix at the Same Time So It Does Not Sink Again
Lifting the slab solves the symptom. Keeping water away from the apron solves the cause. Two things are worth doing at the same time as the lift.
Move your downspout discharge. If a downspout empties within a few feet of the garage opening, it is pouring water directly into the soil under the apron. An extension carrying that water six to ten feet away removes the single biggest source of erosion.
Seal the joints. The joint where the apron meets the garage floor, and the one where it meets the driveway, should be sealed with a flexible caulk. An unsealed joint is an open funnel.
A lifted apron with a fixed downspout and sealed joints is a repair that holds. A lifted apron with a downspout still dumping at the garage door will eventually settle again, and no foam can prevent that.
Frequently Asked Questions
The gap under my garage door lets water in every spring. Will lifting the apron fix that?
Usually, yes. In most cases the gap exists because the apron dropped away from the door seal, and raising the slab back to grade restores contact. Lifting also corrects the slope so water runs down the driveway instead of pooling at the door. If your door itself is out of alignment, that is a separate repair, and you will be told if that is what we see.
My apron has a big crack across it -- can it still be lifted?
Often, yes. A single crack through an otherwise solid slab is common and does not usually rule out lifting, since the two halves can be raised together and the crack sealed afterward. What rules it out is a slab broken into several loose pieces that move independently. Send a photo and you will get a straight answer on which one you have.
How long does a lifted driveway apron last?
The foam itself does not break down, compress, or wash away, so the material is not the limiting factor. What determines the lifespan is whether the water that caused the original settlement has been redirected. With drainage corrected and joints sealed, a properly lifted apron holds for many years.
Will lifting the apron damage my garage floor or the foundation?
No. The foam is injected only under the apron slab and expands into the empty space beneath it, and the lift is monitored continuously so the slab rises evenly and stops at the right elevation. The garage floor and foundation sit on separate support and are not affected.
Can you lift just the apron without touching the rest of my driveway?
Yes. The apron is its own slab section, and lifting it is a standalone repair. Many driveways in Edina, Plymouth, and Bloomington have one settled apron and thirty feet of perfectly level concrete behind it. There is no reason to touch the parts that are fine.
Is there a bad time of year to do this in Minnesota?
Foam lifting can be done in cold weather, but the ground needs to be workable, so the practical window in the Twin Cities runs from spring thaw through late fall. Spring is the busiest stretch, since that is when winter damage becomes obvious. Most homeowners who call in spring get scheduled within two weeks.
If the concrete where your driveway meets your garage has dropped, Benchmark Concrete Raising lifts it back to grade in about two hours using polyurethane foam, and you can park on it that afternoon. If you are in Edina, Plymouth, St. Louis Park, Bloomington, Minnetonka, Eden Prairie, or Maple Grove, send us a photo of the gap and we will give you an honest assessment before you commit to anything.
