Sinking Garage Floors & Apron Gaps: Causes and Fixes

Why Your Garage Floor Starts Sinking and Cracking

We recently got a call from a homeowner — let’s call her Sara — who was worried about her two-car garage. She told us the concrete slab had several large cracks, parts of it seemed to be sinking, and she’d discovered what she called a “mystery hole” right where the asphalt driveway meets the concrete garage floor.

She dropped a tape measure into the gap, and it went down almost two feet. The opening at the surface was only a few inches, but below it was just…empty. If that sounds familiar, you’re not alone — we see this combination of a sinking garage floor and a void at the driveway apron all the time.

In this post, I’ll walk you through what causes these problems, what’s actually going on under the concrete, when it’s a safety or structural concern, and how concrete pressure lifting usually fixes it.

What’s Really Going On Under Your Garage Slab

Most garage slabs don’t fail overnight. They settle slowly over years. A few common culprits are almost always involved:

• Poor or washed-out base material – If the gravel or soil under the slab wasn’t compacted well, it compresses over time. Water from rain, snowmelt, or downspouts can also wash fine material away and leave pockets.
• Water at the garage/driveway seam – The joint where asphalt meets concrete is a prime spot for water to sneak down. Once water gets past that seam, it follows the path of least resistance and erodes the base under the slab.
• Freeze–thaw cycles – In colder climates, moisture in the soil expands when it freezes and contracts when it thaws. That movement can break up the base and open voids under your concrete.

Over time, the slab loses support in sections, which is why you see:

• Cracks spreading from the weakest points
• Slab edges dropping near the garage door
• Gaps or “bottomless” holes along the driveway apron

Why That Driveway Apron Gap Gets So Deep

When Sara told us she had a 6" by 1" opening that went down nearly two feet, we knew she was describing a classic apron void. It usually forms like this:

• The seam between asphalt and concrete opens slightly over time.
• Water runs down into that hairline gap instead of away from it.
• The water washes out the base under the front edge of the garage slab.
• A hollow pocket forms, and the slab edge starts to hang in mid-air.

You only see a narrow opening at the surface, but underneath, the void can extend back under the slab by a foot or more. Left long enough, a vehicle tire loading that unsupported edge can make the concrete crack or suddenly drop.

Safety and Structural Red Flags to Watch For

Not every crack is an emergency, but some signs tell us it’s time to step in:

• Noticeable height differences between sections of your garage floor (trip hazard, especially at the door).
• Cracks wider than a quarter inch or that change height from one side to the other.
• Visible gaps where the garage slab meets the driveway, especially if you can see dark space underneath.
• Doors that don’t close right or garage doors that leave daylight at one corner.
• Hollow sounds when you tap parts of the slab with a hammer or heavy tool.

If any of these sound like your situation, it’s a good idea to have a professional take a look before the damage gets more extensive (and more expensive).

How Concrete Pressure Lifting Raises a Sinking Garage

When Sara asked, “Can this actually be fixed, or do I need to replace the whole thing?” we walked her through our pressure lifting process. Here’s how it typically works:

1. Inspect and map the problem
   We look at the cracks, measure how far the slab has settled, and probe for voids along the apron and under the main floor.
2. Drill small holes
   We drill a series of small holes (usually around the size of a quarter) in the slab in strategic spots. These become access points under the concrete.
3. Inject lifting material
   Using special equipment, we pump a grout or foam material beneath the slab under controlled pressure. This fills the voids and gently lifts the concrete back toward its original level.
4. Monitor elevation as we lift
   We watch the height of the slab carefully, taking small, controlled lifts to avoid over-raising or stressing the concrete.
5. Patch and clean up
   Once the slab is stabilized and leveled, we patch the injection holes and clean the work area. Most homeowners can drive on the slab again either the same day or shortly after, depending on the material used.

This approach usually costs significantly less than tearing out and replacing an entire garage slab, and it directly addresses the voids causing the problem.

When Lifting Works vs. When You Need Replacement

During an estimate, one of the biggest questions we answer is whether lifting is appropriate or if replacement is the better long-term choice. In general:

Good candidates for pressure lifting

• Concrete that’s settled but largely intact
• Cracks that are mainly from movement, not from severe crumbling
• Apron voids where the slab edge is still mostly solid
• Slabs that have dropped an inch or two, but not several inches at multiple broken points

When we recommend replacement

• Extensive cracking where the slab is broken into many loose pieces
• Severely deteriorated or crumbling concrete
• Major settlement combined with structural issues in the surrounding foundation
• Situations where lifting would cost almost as much as a full replacement but with less long-term benefit

The goal of our estimate is always to be honest about what will actually solve the problem for the long haul, not just what’s possible in the short term.

What to Expect During an Estimate and Repair Visit

Sara was working from home, like a lot of our customers, so she asked how much of her day this would take. Here’s what homeowners can typically expect.

During the estimate

• We walk the garage and driveway with you and listen to your concerns.
• We check slab heights, cracks, and the apron joint, and look for drainage issues.
• We explain whether lifting, replacement, or a combination makes the most sense.
• You get a written estimate so you can decide on timing and budget.

During the repair

• We set up equipment outside and inside the garage and protect nearby areas as needed.
• Drilling, lifting, and patching usually take a few hours for a typical two-car garage.
• You’ll hear some drilling and pumping, but we keep things as tidy and contained as possible.
• We walk you through the results before we leave and discuss any maintenance tips to help prevent future settlement.

Wondering If Your Garage Slab Is Still Salvageable?

If you’re seeing the same signs Sara did — sinking spots in the garage, long cracks, or that “bottomless” gap where the driveway meets the slab — it’s worth having it checked before the damage spreads.

Concrete pressure lifting is often a fast, cost-effective way to restore a safe, level garage floor and re-support that vulnerable apron edge. And if your slab is too far gone, a good inspection will at least give you a clear plan for replacement instead of guesswork.