Signs Your Garage Slab Needs Replacing

Garage floors get the worst of everything: cars drip road salt on them all winter, slush freezes on them overnight, and they were usually poured last and thinnest when the house was built. In Lake County, where a lot of the housing stock dates to the 1960s through 1980s, original garage slabs are past their service life. This guide sorts the symptoms into replace, repair, and live with.

The Diagnosis Table

Symptom	What it usually means	Replace, repair, or live with
Slab pitches toward the house	Poured wrong or door end settled	Replace. Cannot be regraded in place
Whole slab or a large area more than 1 inch low	Base failure: fill under the slab settled	Replace
One corner or one section low, ground stable	Local settlement	Repair: polyurethane or mudjack lift
Heaves at the door every winter, drops in spring	Water under the threshold freezing; no base or bad drainage	Replace with proper base, thickened edge, and drainage
Scaling or pitting across most of the floor	Non-air-entrained concrete plus decades of salt	Replace. Overlays over widespread scaling fail
Scaling in one spot under a drip line	Salt concentration	Repair: patch, then keep salt off
Crack that has opened wider than 1/4 inch or has one side higher	Base movement	Replace if it is still moving; lift and epoxy if it has stopped
Hairline cracks that do not move	Normal shrinkage, no joints cut	Live with, or epoxy for looks
Random cracking in a grid pattern, edges lifting	Slab poured too thin on a bad base, or over a buried void	Replace
Oil and rust staining	Cosmetic	Live with, or clean and coat
Water pooling in the middle	Slab dished from settling or poured flat	Replace if more than 1/2 inch; otherwise live with

Replace: The Four Clear Cases

Pitch toward the house. A garage slab should fall 1/8 inch per foot toward the door so melting slush leaves the building. When it falls the other way, water runs to the back wall, wicks into the framing and drywall, and often into the basement or crawlspace through the foundation. Nothing fixes the pitch except a new slab. This is the one we see most on 1970s tract houses where the garage was an afterthought.

Settled more than an inch. Garages are commonly built over the backfill from the foundation excavation, which was never compacted. Over 20 years it consolidates and the slab sinks with it, leaving a gap under the door threshold and a step down from the house. Lifting can work when a section drops; when the whole floor has sunk, it is a base failure and the slab comes out.

Scaling across the floor. Original garage slabs were often poured without air entrainment because nobody expected them to see freeze-thaw. Then thirty winters of salt brine dripping off cars did what salt does. When the flaking covers most of the floor, the surface is gone, and an overlay bonded to a failing surface fails with it.

Annual heaving at the door. The threshold is where water collects and where the slab edge is exposed to the outside air. On no base, it freezes and lifts an inch every January and drops in April, and the crack a foot inside the door gets wider each year. The fix is a thickened, reinforced edge on a drained stone base, which is how we pour every garage threshold.

Repair: When It Is Local

If the ground under the slab has finished settling, which is the usual case on a 30-year-old garage, a single low section can be lifted with polyurethane foam injected through small holes. It is fast and costs a few hundred to about a thousand dollars. Cracks that are not moving can be routed and filled with epoxy or polyurea. A spalled area under a drip line can be patched with a polymer-modified repair mortar, though patches never match and never last as long as the slab.

The test for repair versus replace is movement. Mark the crack with a pencil line across it and check in the spring. If the halves have shifted, it is still moving and a repair is a delay, not a fix.

Live With It

Hairline shrinkage cracks that do not displace, oil stains, rust from a dropped tool, minor pitting in a low-traffic corner: none of these threaten the slab. Clean it, coat it if you want it to look better, and spend the money on the driveway.

What A Replacement Involves

We saw-cut around the perimeter to protect the foundation walls, break out the old slab, and haul it away. That is the part that decides price: a slab we can break and wheel out through the door costs less than one that needs a mini-excavator inside. Then the subgrade is cut to depth and re-compacted, 4 inches of #57 limestone goes down and is compacted, and a vapor barrier goes over the stone so moisture from the ground stays out of the concrete.

The pour is 4,000 psi air-entrained concrete, 4 inches thick across the floor and 5 at the door with a #4 rebar bar along the threshold, fiber throughout, pitched 1/8 inch per foot to the door, with a hard-trowel finish that is smooth enough to sweep and ready for an epoxy coating after 60 days. Control joints are cut the same day in a grid that puts the cracks where they belong. Walk on it at 48 hours, park on it at 7 days.

If the garage is attached and the old slab ran under the framing, we discuss that at the site visit; it changes the saw-cut plan. If the community inspects interior flatwork, the permit is on the quote.

Cost In Lake County, 2026

Garage	Square feet	Installed with tear-out
One-car, 12 × 22	264	$2,900 – $4,000
Two-car, 20 × 22	440	$4,800 – $6,600
Three-car, 30 × 22	660	$7,300 – $9,900

Add a driveway or apron at the same time and the second item prices lower because the crew and equipment are already there. Every job comes with a written, itemized quote within 48 hours of the site visit and the one-year come-back guarantee on grading, settling, and surface defects.