A crack in your driveway or patio is concrete telling you a story about what happened underneath or inside it, and most homeowners never stop to read it. They either panic and tear out a slab that had another 15 years in it, or they patch over a problem that’s going to come back twice as expensive in two years. The difference between a smart repair and wasted money usually comes down to understanding three things: hairline cracking versus structural cracking, surface spalling versus deep deterioration, and cosmetic settlement versus soil failure underneath the slab.
Start With the Crack: Width, Direction, and Movement
Not all cracks mean the same thing. A crack under 1/8 inch wide in a driveway or sidewalk is usually shrinkage cracking from the original pour, caused by water leaving the concrete faster than it could cure evenly. This happens in nearly every slab ever poured and rarely affects structural performance. Cracks between 1/8 inch and 1/4 inch deserve a closer look, especially if they run in a straight line across the full width of a slab or follow a control joint pattern. Anything wider than 1/4 inch, especially if one side of the crack sits higher than the other, points to movement below the slab rather than surface shrinkage.
Direction matters too. Cracks that run parallel to a slab edge or follow a control joint are often normal. Cracks that run diagonally from a corner, or that branch like a tree, usually mean the load path through the slab has changed, which happens when soil underneath has eroded, compacted unevenly, or frozen and thawed repeatedly.
- Hairline cracks under 1/8 inch: cosmetic, patch with a flexible polyurethane sealant
- Cracks 1/8 to 1/4 inch with no vertical offset: monitor, then repair with epoxy or semi-rigid filler
- Cracks over 1/4 inch or with offset greater than 1/4 inch: get a soil and structural assessment before patching
- Cracks that reopen within a year of filling: the underlying cause hasn’t been addressed
A simple test: mark both ends of a crack with a pencil and the date, and check it again after a freeze-thaw cycle or a hard rain. If it grows more than 1/16 inch in a season, you’re dealing with active movement, not old damage.
Spalling: When the Surface Is Failing, Not the Slab Itself
Spalling is the flaking, pitting, or chipping you see on the top layer of concrete, usually caused by one of a handful of culprits: deicing salt, freeze-thaw cycling in concrete that wasn’t air-entrained correctly, too much water in the original mix, or steel reinforcement rusting and expanding just below the surface. Surface spalling that’s shallow, under 1/2 inch deep and not exposing rebar, is almost always repairable. Deep spalling that exposes corroded rebar is a different animal, because rusting steel expands up to seven times its original volume and will keep cracking the surrounding concrete even after you patch it.
Check for spalling by tapping the surface with a hammer or the butt end of a screwdriver. A solid, sharp sound means good concrete underneath. A hollow or dull thud means the surface layer has delaminated from the slab body, and surface patching material won’t bond well to it. In that case the loose material needs to be chipped out down to sound concrete, typically 1 to 2 inches deep, before any repair mortar goes in.
- Light surface spalling: grind and apply a polymer-modified resurfacer, roughly 1/8 to 1/4 inch thick
- Moderate spalling with hollow spots: chip out to sound concrete, prime, and patch with a bonding agent plus repair mortar
- Spalling with exposed, rusted rebar: cut back the rebar, treat it with a rust inhibitor or replace the section, then patch
- Spalling covering more than 25% of a slab’s surface: resurfacing the whole slab is usually cheaper than patching dozens of spots
Settlement: The Difference Between Cosmetic Dip and Structural Problem
Settlement is the scariest-looking issue and the one most likely to get a homeowner quoted for full replacement when they didn’t need it. A slab can settle because the fill soil under it was never compacted properly when the house or patio was built, because water has eroded a void underneath, or because organic material in the base decomposed over time and left a gap. The fix depends entirely on how much the slab has moved and whether that movement is still happening.
A settled slab that has dropped less than 1 inch and has been stable for at least a year or two is often a good candidate for slabjacking or polyurethane foam injection, which lifts the existing concrete back to grade by pumping material underneath it through small holes, usually 5/8 inch to 1 inch in diameter. This costs a fraction of replacement and can be done in a single day for most driveways and walkways. A slab that has dropped more than 2 inches, that’s still actively sinking, or that shows cracking radiating from multiple points usually has a soil or drainage problem that needs to be fixed first, or the lift won’t hold.
Check the drainage around any settled slab before deciding on a fix. Downspouts dumping water next to a foundation or patio edge, grading that slopes toward the house instead of away from it, and sprinkler heads that spray directly onto a slab edge are the three most common causes of the erosion that leads to settlement. Fixing the water source first is non-negotiable, because lifting a slab back to level without addressing drainage just buys you a repeat problem in a few years.
When Repair Is the Right Call
Repair makes financial and practical sense more often than most homeowners assume, especially for slabs under 10 years old or in generally good condition aside from the specific problem area.
- Isolated cracking under 1/4 inch wide with no vertical offset
- Surface spalling affecting less than a quarter of the total slab area
- Settlement under 2 inches that has stabilized and has a known, fixable drainage cause
- Control joint failure where the joint itself has crumbled but the surrounding slab is sound
- Cosmetic damage from stains, minor scaling, or small chips that don’t affect structure
Cost is the other half of the equation. Crack repair with epoxy injection or polyurethane sealant typically runs $5 to $15 per linear foot. Resurfacing a spalled patio or driveway runs $3 to $10 per square foot depending on thickness and prep work. Slabjacking generally costs 30 to 50% less than full replacement of the same area. If a repair costs less than a third of what replacement would cost and addresses the root cause, it’s almost always worth doing first.
When Replacement Is the Honest Answer
Some conditions make repair a waste of money no matter how good the contractor is. A slab with cracking across more than 50% of its surface, in multiple directions, has likely lost structural integrity throughout, not just in the visible crack lines. Concrete that’s crumbling or can be scraped away with a screwdriver, rather than just chipped at specific spots, has usually suffered chemical deterioration from something like alkali-silica reaction or severe freeze-thaw damage that goes all the way through the slab.
- Cracking across the majority of the slab in multiple directions
- Widespread crumbling or scaling that goes beyond the surface layer
- Settlement over 3 inches or still actively progressing after drainage fixes
- A slab older than 25 to 30 years showing multiple failure types at once
- Reinforcement so corroded that more than 20% of the rebar in a section needs replacement
In these cases, patching individual problems is a short-term fix on a slab that’s failing as a whole, and most of that repair cost gets thrown away once replacement becomes unavoidable a year or two later.
Getting an Honest Assessment Before You Spend Money
The fastest way to waste money on concrete is to get a quote from someone who only does one type of work, because a replacement contractor will often recommend replacement and a patching crew will often recommend patching. Ask any contractor you’re considering to explain specifically why they’re recommending repair or replacement based on crack width, spalling depth, and settlement history, not just a visual guess. Homeowners dealing with driveway cracking, patio settlement, or spalled walkways in the South Sound area can get a straightforward evaluation from a contractor offering concrete repair in Tacoma who will check soil conditions and drainage before quoting a fix, rather than defaulting to the most expensive option.
Before you call anyone, take photos of every crack and problem area with a tape measure in the shot, note the date, and check back in 60 to 90 days to see what’s changed. That record turns a vague conversation about a few cracks into a clear case for the specific repair or replacement your slab actually needs.
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