We earn a commission if you buy through links on this page, at no cost to you. How we choose products
For a crack in a driveway, patio or floor from hairline up to 1/4 inch wide, the best concrete crack sealer is a flexible polyurea top over dry sand soaked in urethane, as in the UV slab kit. Joints take a polyurea joint filler, and basement wall cracks get foam injection instead. A penetrating sealer rolled over the whole slab is a different product: it protects the concrete after the cracks are fixed, but its data sheets say it isn't meant to seal cracks.
A concrete crack sealer keeps water out of a crack. The right one depends on whether you’re sealing a crack in a slab, a joint, a basement wall or the whole surface, because each takes a different product.
What is the best concrete crack sealer?
For slab cracks from hairline up to 1/4 inch, a flexible polyurea sealant over a sand and urethane fill. Outdoors, that’s the UV slab kit; indoors, the urethane slab kit does the same job without the UV-resistant top.
The table sorts the main types of crack sealer for concrete by what each one is for.
| Type | What it is | Best for | Limits |
|---|---|---|---|
| Polyurea over sand and urethane | Sand fills the depth, flexible polyurea seals the top | Outdoor slab cracks from hairline to 1/4 inch (the indoor kit skips the polyurea) | Concrete at least 50°F; must be clean and dry |
| Polyurea joint filler | Flexible polyurea pumped into a joint | Control and expansion joints | Made for joints, not random cracks |
| Self-leveling sealant in a tube | Flexible sealant that flows flat | Joints and wide cracks, over backer rod | Depth set by backer rod, not sand |
| Gravity-fed resin (sealer/healer) | Thin resin poured on so it soaks into fine cracks | Fine cracks that have stopped moving | Not for moving cracks |
| Penetrating sealer | Silane, siloxane or siliconate that soaks into the surface | The whole slab after cracks are fixed | Not intended to seal cracks |
| Polyurethane foam injection | Foam pumped through ports into a wall crack | Leaking or damp poured basement wall cracks | Not for structural cracks |
Concrete Sealers USA slab kit, joint kit, foam kit and PS-series data sheets; ACI RAP-2; U.S. Bureau of Reclamation repair guide
What’s the difference between a crack filler, a crack sealant and a concrete sealer?
A filler fills the crack’s depth, a sealant seals its top so water can’t get in, and a concrete sealer protects the whole surface. Many products are sold as “crack sealers” but do only one of those jobs.
The UV slab kit does the first two: sand and urethane fill the depth, and the polyurea top seals it. A penetrating concrete sealer does the third. The sealer maker’s FAQ says sealers are not fillers and that any crack wider than 1/16 inch should be repaired first.
The penetrating vs topical sealer comparison explains the surface sealers in detail.
Which crack sealer works on driveways and patios?
The UV slab kit. Its data sheet describes the polyurea top as UV resistant and lists 170 percent elongation, so it stays flexible in sun and through temperature swings.
The method, from the kit’s data sheet:
Prepare the crack
Grind cracks 1/8 inch and narrower to 1/4 inch wide by 1/4 inch deep. Wider cracks, up to 1/4 inch, aren’t ground. Clean the crack and make sure it’s dry.Prime it
Wet the inside of the crack with urethane.Add sand
Pour dry silica sand into the crack to within 1/4 inch of the top.Soak the sand
Saturate the sand with urethane and wait about 30 minutes.Seal the top
Fill the last 1/4 inch with the polyurea. It levels itself; scrape it flush with a razor scraper.
The data sheet gives light traffic in 30 minutes and full traffic in 60 minutes at 70°F. The sand isn’t in the kit, and the small kit needs a standard caulk gun. The driveway crack guide and the patio crack guide cover each surface.
Which sealer works on indoor floor cracks?
The urethane slab kit, for basement and garage floors. Its data sheet gives a 2 to 4 minute initial set and back in service within 20 minutes. The product page says it cures tan and isn’t UV stable, which doesn’t matter out of the sun.
The method is the same idea without the polyurea top: wet the crack with urethane, pour in dry sand and saturate it, add sand until the crack is full and soak it to a slight hump, then scrape it flush when it turns light gray at initial set. For a garage apron or any crack in direct sun, use the UV kit instead. The garage floor crack guide and the basement floor crack repair guide go step by step.
Can a penetrating sealer seal hairline cracks?
Only the very finest ones. The U.S. Bureau of Reclamation’s repair guide says penetrating sealers seal cracks about 0.002 inch or smaller (opens in a new tab), but they don’t bond the crack back together.
The penetrating sealer data sheets say the products are not intended to seal cracks. For a slab with crazing or lots of fine lines, sealing the whole surface is still the practical answer. For one or two visible hairlines, a thin hairline crack filler goes into the crack first.
Outdoors, the NRMCA recommends a commercial breathable sealer (opens in a new tab) to protect against freeze-thaw damage, since water expands as it freezes. A siloxane water repellent is that kind of sealer.
What about pour-on sealer/healer resins?
They’re a method for fine, stable cracks across a floor or deck. The thin resin is poured or flooded over the surface and soaks down into the cracks.
The American Concrete Institute’s bulletin on this method says it’s for cracks that are not moving (opens in a new tab), such as shrinkage cracks, and that it’s not effective for moving cracks. Successful repairs have been documented in cracks less than 0.006 inch wide, and the bulletin calls for letting the area dry at least 24 hours first.
For most homeowners with a few cracks, the slab kit is simpler. The retail vs pro grade comparison covers where pro methods differ.
Which sealer goes in a control or expansion joint?
A flexible joint filler, because a joint is made to move. The polyurea joint kit’s data sheet gives coverage for joints 1/8 to 1/4 inch wide and 3/4 to 2 inches deep.
Wider joints get backer rod and a flexible joint sealant instead. The expansion joint repair guide covers both methods.
How do you seal a crack in a basement wall?
With foam injection, not a surface sealer. A polyurethane foam crack injection kit fills the crack through the wall’s thickness, so water can’t go around the seal.
The foam’s maker rates the 10 ft kits for cracks up to 3/8 inch and says they’re not intended for structural cracks. This site’s rule is stricter: a wall crack wider than 1/4 inch, a horizontal crack, a bowing wall, a stair-step crack in block or a crack with offset edges goes to an engineer before any kit. The foundation crack repair kits roundup compares the kits, and the epoxy vs polyurethane comparison explains the resins.
Do hardware store crack sealers work?
Many do, on the right crack. Store sealants from brands like Sika, Quikrete and DAP are mostly self-leveling or gun-grade sealants in a tube, sold for both cracks and joints.
The usual weak point is depth. A sealant in a tube fills only as deep as it’s pushed, so a deep gap needs something under it: backer rod in a joint, or sand in a crack. The reviews of Quikrete Crack Seal and DAP concrete crack filler compare their labels with the slab kit, and the best concrete crack filler guide sorts fillers by crack type.
When should you not seal a crack?
When it’s still moving or you don’t know why it’s there. A crack wider than 1/4 inch, one with one side higher than the other, or a crack in a sinking slab needs its cause found first. The large crack guide covers when a wide crack is still a DIY job.
The U.S. Bureau of Reclamation’s guide says it’s better to leave most cracking unrepaired (opens in a new tab) than to make an inadequate repair. The product chooser asks a few questions about your crack and points to the right product.
Once the crack is sealed and cured, the sealing after crack repair guide covers which surface sealer to use and how long to wait.
Questions
Will a crack sealer stop a crack from getting bigger?
No. A sealer keeps water out of the crack, which slows freeze damage, but it doesn't stop whatever is moving the slab. The American Concrete Institute says the cause of cracking has to be corrected before a structural repair.
Is crack sealer the same as caulk?
Close. Flexible crack sealants come in caulk-style cartridges, but they're made to bond to concrete and stretch with it. Before using a caulk on a driveway, check that its label says it's made for concrete and outdoor use.
Can I seal concrete cracks in cold weather?
Only within the label's limits. The polyurea in the UV slab kit and the joint kit needs concrete at least 50°F when it goes on, per its data sheet. Below that, wait for a warmer day.
Should I seal the whole driveway after sealing the cracks?
Outdoors, it helps. The NRMCA recommends a breathable sealer to protect concrete from freeze-thaw damage. Seal the cracks first, let them cure, then seal the slab.