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Fill sidewalk cracks up to 1/4 inch wide with flush edges using a UV-stable crack kit: urethane over packed sand, topped with a gray polyurea that takes foot traffic in 30 minutes at 70°F. If one slab sits higher than the next, that's an uneven sidewalk and a trip hazard, and filling won't fix it; the slab needs grinding, lifting or replacing. If the sidewalk runs along the street, check with your city first, because who has to fix it varies by city.
Before you start
A crack you can fill and a sidewalk trip hazard look alike from a distance. Check for these first.
- One slab sits higher or lower than the one next to it
- The crack is wider than 1/4 inch
- The sidewalk is along the street, where your city may set the rules
If any of these fit, find out who to call first: a structural engineer or a repair contractor.
Is it a crack or a sidewalk trip hazard?
Lay a straightedge across the crack. If both sides are flush and the crack is 1/4 inch or narrower, it’s a crack you can fill; if one side sits higher, it’s a sidewalk trip hazard, and filler won’t level it.
The federal ADA accessibility standards give a useful yardstick for how much of a lip is too much. They allow a change in level of up to 1/4 inch (opens in a new tab) to be vertical, require anything from 1/4 to 1/2 inch to be beveled, and require a ramp above 1/2 inch.
The same standards say openings in a walking surface shouldn’t let a sphere more than 1/2 inch (opens in a new tab) pass through. That’s a design standard for accessible public routes, not a rule for your front walk, but it shows where a lip or gap starts catching shoes and wheels.
What do you need for sidewalk crack repair?
A UV-stable crack kit, dry silica sand and a few hand tools. A sidewalk sits in full sun and gets walked on, so the filler has to flex with the slab and hold up to sunlight.
- Straightedge and tape measure
- Tuckpoint grinder with a diamond blade, for cracks 1/8 inch and narrower
- Safety glasses, dust mask and gloves
- Shop vacuum, stiff brush and a weeding tool
- Dry silica sand
- Caulk gun and razor scraper
Not sure this kit fits your crack? The product chooser sorts fillers by width and location.
How do you fix a crack in a sidewalk?
Pull the weeds, open up thin cracks, clean and dry them, pack them with sand soaked in urethane, then top them with a polyurea filler. That’s the method in the UV slab kit’s instructions, for cracks up to 1/4 inch with flush edges.
Check the edges
Lay a straightedge across the crack. If one side is higher, or the crack is wider than 1/4 inch, read the section on uneven sidewalks first.Pull the weeds
Pull out weeds and roots, then scrape the soil out of the crack with a screwdriver or weeding tool.Open up thin cracks
For cracks 1/8 inch wide or less, the kit’s instructions say to grind the crack out to 1/4 inch wide and 1/4 inch deep so the filler has room to grip. Wider cracks skip this step.Clean and dry the crack
Vacuum out the dust, soil and loose concrete. The instructions say it’s critical that the crack be dry, so work after a few dry days.Prime with urethane
Wet the inside of the crack with the kit’s urethane. Just wet it, don’t fill it.Pack in sand
Pour dry silica sand into the crack until it’s 1/4 inch below the surface.Soak the sand
Saturate the sand with more urethane and let it set for about 30 minutes.Top it off
Fill the last 1/4 inch with the polyurea filler. It’s thin and levels itself.Scrape it flush
Scrape any overflow flush with a razor scraper. A ridge left on a sidewalk is its own small trip edge.
The University of Missouri Extension’s guide to sidewalk cracks says to repair only when concrete is dry (opens in a new tab), and that a repair creates a safer walking surface. The polyurea top is gray, so it shows as a thin gray line on most sidewalks.
How long before you can walk on a repaired sidewalk?
About half an hour in mild weather. The polyurea top takes light foot traffic in 30 minutes and full traffic in 60 minutes at 70°F, according to its data sheet, and the concrete has to be at least 50°F when you apply it.
| Material | Apply between | Light use | Full cure | Source |
|---|---|---|---|---|
| Urethane and sand (first layer) | Dry crack | Let it set about 30 minutes | Then add the polyurea top | Kit instructions |
| Polyurea top | Concrete at 50°F or warmer | Light traffic in 30 minutes at 70°F | Full traffic in 60 minutes at 70°F | Polyurea data sheet |
Cold slows every cure. Rope off the section or put out a cone until the top is ready, so nobody steps in it.
How do you fix an uneven sidewalk?
By grinding the high edge down, lifting the low slab back up, or replacing the slab. Those are contractor jobs, and none of them is a crack filler.
- Grinding. A contractor grinds or cuts a bevel on the raised edge. It suits a small lip on a slab that has stopped moving.
- Lifting. A sunken slab can often be raised back into place by pumping material under it. The sinking slab guide compares mudjacking and foam lifting.
- Replacing. A slab that’s broken into pieces, or pushed up by a tree root that’s still growing, usually gets torn out and poured again. The repair or replace guide helps you decide.
Find out why the slab moved before you pay for any of these. A root that’s still growing or a downspout soaking the soil will move the slab again.
Which sidewalk fix do you need?
Match what you see to the fix before you buy anything. Most sidewalk cracks only need filling; uneven slabs need more.
| What you see | What it usually means | Fix |
|---|---|---|
| Crack up to 1/4 inch, flush edges | Shrinkage or freeze-thaw cracking | Fill it with the UV slab kit: urethane over packed sand, polyurea on top |
| Weeds growing in the crack | Soil and seeds in an open crack | Pull them, dry the crack, then fill it |
| One slab higher than the next | Tree root, frost heave or settled soil | Grind, lift or replace; check with your city if it's public |
| Slab sunk or tilted | Soil washed out or settled under it | Lift or replace, not filler |
| Cracks everywhere, crumbling surface | Slab near the end of its life | Repair or replace |
Who is responsible for fixing a cracked sidewalk?
It depends on your city. For the public sidewalk along the street, some cities make the property owner responsible for repairs and others do the work or share the cost, so check your city’s public works or street department page before you hire anyone.
New York City is one example. Its 311 service says property owners are responsible (opens in a new tab) for installing, maintaining and repairing the sidewalks next to their property, and lists loose, cracked, uneven or missing sections as defects. The same page says the city’s Parks Department may repair sidewalk damaged by city street trees at no cost for some one to three family homes.
Rules like these also cover who can do the work, whether you need a permit, and how the new slab must be built. Who is liable if someone trips is a legal and insurance question that depends on your city and your policy, so ask your insurance agent or a local attorney rather than relying on a general guide.
What mistakes make a sidewalk crack repair fail?
Moisture, weeds and filling a slab that has moved. Each one can make the filler let go early.
- Filling a damp crack. The kit’s instructions call a dry crack critical, and the Missouri Extension guide says the same.
- Leaving roots in the crack. Weeds grow back through soil left at the bottom. Cornell University’s weed guide lists causing and expanding cracks in pavement (opens in a new tab) among the damage weeds do.
- Skipping the grinding on a thin crack. The kit’s instructions call for grinding cracks 1/8 inch and narrower out to 1/4 inch wide and deep, so the filler has room to grip.
- Filling a lip instead of fixing it. Filler in a crack with one side higher leaves the trip edge exactly where it was.
- Working in the cold. The polyurea data sheet calls for concrete at 50°F or warmer.
Why do sidewalks crack and heave?
Mostly from water, freezing, salt and tree roots. Sidewalks are thin slabs on soil, so anything that moves the soil moves the slab.
- Freeze-thaw. The NRMCA explains that water in saturated concrete expands as it forms ice and this causes stresses (opens in a new tab) that crack and flake the surface.
- De-icing salt. The same NRMCA sheet says heavy use of de-icers increases potential for scaling (opens in a new tab).
- Tree roots. Roots growing under a slab lift it from below.
- Joints too far apart. The NRMCA’s guide to joints in concrete slabs (opens in a new tab) explains that joints control where a slab cracks as it shrinks. Without enough of them, the slab cracks on its own between them.
The why concrete cracks guide and the concrete cracks hub cover the other outdoor slabs.
How do you keep a repaired sidewalk from cracking again?
Keep water and salt out of it. Once the repair cures, seal the sidewalk with a penetrating sealer, and go easy on de-icers.
The NRMCA recommends sealing the surface with a commercial breathable sealer (opens in a new tab) to protect concrete from freeze-thaw damage, and suggests clean sand for traction. Keep downspouts from draining onto or beside the sidewalk.
The sealing after crack repair guide covers which sealer to use over a repair and how long to wait.
Questions
Can I grind down a raised sidewalk edge myself?
It's a job for a concrete contractor. Grinding concrete takes a heavy grinder and makes a lot of dust, and lifting a sunken slab takes special equipment. On a public sidewalk, your city may also have rules about who can do the work.
Can I fill sidewalk cracks in winter?
Only on a mild, dry day. The polyurea's data sheet calls for concrete at 50°F or warmer, and the crack has to be dry. The cold weather guide covers timing by season.
Should I fill the straight lines across the sidewalk?
Those are control joints, not cracks. They're cut so the sidewalk cracks along them as it shrinks. If you want them sealed against water and weeds, use a joint filler made for control joints.
A tree root lifted my sidewalk. Will filling the crack help?
No. The root keeps pushing, so the crack and the lip come back. The slab needs lifting or replacing, and on a public sidewalk the tree may belong to the city, so call them first.