Not every crack in your concrete means the same thing, and the fix depends entirely on why it cracked. We see homeowners in Crystal Lake do one of two things, and both can be mistakes: caulk a crack that’s actually a sign of a slab settling, or tear out and replace a slab over a crack that a bead of sealant would have handled fine.
What caulking actually does
Filling a crack with a flexible sealant is a real repair for the right kind of crack. It keeps water out, which matters a lot in our climate, because water in a crack freezes, expands, and pries the crack wider every winter. Sealing a stable hairline crack stops that cycle and keeps the surface looking clean.
Where sealant is the right call is on cosmetic cracks. Concrete shrinks a little as it cures, and thin shrinkage cracks show up in almost every slab within the first year. Control joints, those grooves cut into a driveway or sidewalk, are there specifically to make concrete crack in a straight, hidden line instead of a random one. Cracks that follow those joints, hairline cracks that aren’t offset, surface crazing that looks like a road map: these are appearance issues. Clean them, seal them, move on.
What caulking can’t fix
Here’s the part that gets people. A caulk gun does nothing about what’s under the slab. If a crack opened because the ground beneath the concrete settled, sealing the top is cosmetic, and the movement keeps going underneath it.
The tell is displacement. Run your hand across the crack. If one side sits higher than the other, that slab has moved, and something under it gave way. A hairline you can barely feel is one thing. A crack where the two halves are at different heights, or where the gap is wide enough to drop a coin into, is telling you the support underneath isn’t holding. Sealing that doesn’t repair anything. It hides the symptom while the void, the soil erosion, and the freeze-thaw cycle keep doing their work.
We get calls where someone caulked a settled slab a year ago, and now the lip is bigger and the crack has reopened past the sealant. The caulk didn’t fail because it was bad caulk. It failed because it was the wrong repair for a structural problem.
How to tell which one you’ve got
You can sort most cracks yourself with a few checks before you ever call us:
- Feel for a height difference across the crack. Level on both sides points to cosmetic. A lip points to settling.
- Look at the width. Hairline and consistent is usually shrinkage. Wide, or wider at one end than the other, suggests movement.
- Tap the slab near the crack. A solid thud is good. A hollow sound often means there’s a void under the concrete.
- Check where the water goes. If the cracked section now holds a puddle it didn’t used to, the slab has changed pitch, which means it settled.
- Watch it over a season. A crack that grows, or a lip that gets taller between spring and fall, is active. Active cracks aren’t caulk jobs.
If everything points to cosmetic, sealant is genuinely the answer, and you don’t need us for that. If you’re seeing displacement, hollow spots, or growth, the crack is a symptom and the actual problem is under the slab.
Fixing the cause instead of the crack
When a crack comes from settling, the repair is to support the slab again, not just to fill the line on top. That’s the work we do. Polyurethane foam injection goes in through small ports, expands under the concrete to fill the voids that opened up, and lifts the slab back toward level. Mudjacking does the same job with a soil-based slurry, but does not typically last very long. Once the slab is supported and back to grade, then sealing the crack actually holds, because the two sides aren’t moving relative to each other anymore.
That order matters. Support first, seal second. Do it the other way and you’re sealing a moving target.
There’s also a point where a slab is too far gone for either. Concrete that’s crumbling, badly spalled, or broken into several independent pieces has lost its structural integrity, and lifting a slab that can’t hold together doesn’t work. That’s a replacement, and we’ll tell you when that’s the honest answer. But it’s less common than people expect. A lot of cracked concrete around Crystal Lake is structurally fine and simply sitting on soil that moved.
The short version for your slab
If the crack is thin, level across, and following a joint, seal it and you’re done. If one side is higher than the other, if it sounds hollow, if water pools where it didn’t, or if it’s getting worse, the crack is the visible edge of a settling problem, and caulk will only buy you a season. In that case it’s worth having us look at what’s happening under the concrete so the repair addresses the cause. We’d rather tell you a crack is cosmetic and save you the call than watch you seal over something that needs lifting.
Questions we get
How do I know if a crack is structural or cosmetic?
Feel across it. If both sides are level and the crack is thin, it’s almost always cosmetic. If one side sits higher than the other, or it sounds hollow, the slab has moved and the crack is a symptom of settling.
Can I just caulk a crack in a settled slab?
You can, but it won’t last. Sealant keeps water out of a stable crack. It does nothing about the void or soil movement under a slab that’s dropped, so the crack reopens and the lip keeps growing.
Does a cracked slab always need replacing?
No. A lot of cracked concrete is structurally fine and simply sitting on soil that moved, which means it can be lifted and then sealed. Replacement is for slabs that are crumbling or broken into pieces that can’t be supported.
Should I seal the crack before or after lifting?
After. Support the slab first so the two sides stop moving, then seal. Sealing first just means sealing a crack that’s still opening.