Short answer
You can repair a cracked concrete driveway by cleaning and widening the crack, then filling it with the right product for its size: use a liquid crack filler or thin resurfacer for hairline cracks, a polyurethane self-leveling sealant for 1/8–1/2 inch cracks, and a polymer‑modified repair mortar for wider or broken edges. For sunken or heaved slabs, or widespread spider cracking, consider professional slab leveling or replacement.
What causes the cracks and what to use
Concrete cracks from shrinkage, freeze–thaw cycles, heavy loads, or poor base prep. The fix depends on the crack type and size:
- Hairline (<1/16 in): Fill with concrete crack filler or apply a polymer-modified resurfacer over the area.
- Narrow to moderate (1/8–1/2 in): Use a flexible, self-leveling polyurethane or polyurea joint/crack sealant with backer rod.
- Wide (>1/2 in) or broken edges: Pack with a polymer‑modified concrete repair mortar (or vinyl patch) after proper prep.
- Sunken slabs or ongoing movement: Call a pro for slabjacking/foam lifting and to address base issues.
Tools and materials
- Safety: N95/respirator rated for silica, safety glasses, gloves, knee pads, hearing protection
- Prep: Pressure washer or hose with high‑pressure nozzle, stiff wire brush, shop vac/leaf blower
- Crack routing: Cold chisel and hammer or an angle grinder with a diamond crack chaser blade
- Filling: Caulk gun, closed‑cell foam backer rod (various diameters), margin/pointing trowel, mixing bucket and drill paddle (for mortar), finishing sponge
- Products:
- Liquid concrete crack filler or polymer-modified resurfacer (for hairline)
- Polyurethane or polyurea self‑leveling crack/joint sealant (gray)
- Polymer‑modified repair mortar/vinyl concrete patch (for wide cracks)
- Concrete bonding agent (if using repair mortar)
- Silane/siloxane penetrating sealer (optional but recommended after repairs)
Estimated costs: $8–15 per tube of sealant; $5–10 backer rod; $15–30 per bag repair mortar; $25–40 per bag resurfacer; grinder rental ~$30–50/day; pressure washer rental ~$40–80/day.
Step-by-step
1) Inspect and plan
- Identify crack widths and decide product per section.
- Check for movement: if one side is higher than the other (trip hazard) or the slab has sunk, DIY filling is cosmetic only; consider leveling.
- Check weather: Aim for 50–90°F, dry, shaded if possible. Avoid rain for 24–48 hours.
2) Prep the crack
- Put on PPE. Silica dust is hazardous—avoid dry grinding without a vacuum or water suppression.
- Clean: Pressure wash or scrub to remove dirt, algae, and loose concrete. Let it dry.
- Route/widen: Use a cold chisel or an angle grinder to open the crack to a consistent width and create a slightly V‑shaped profile. This helps the repair key in and last.
- Vacuum out dust and debris thoroughly. Lightly dampen (SSD—saturated surface dry) if using mortar; keep dry for polyurethane sealants.
3) Fill based on size
Hairline cracks:
- Option A: Apply a liquid concrete crack filler. Work it in with a squeegee, let it settle, and reapply if it sinks.
- Option B: For many hairlines, clean and then apply a polymer‑modified resurfacer over the section to blend appearance and seal micro‑cracks.
1/8–1/2 inch cracks (flexible sealant):
- Insert closed‑cell backer rod to control depth and prevent three‑sided adhesion.
- Gun in polyurethane/polyurea self-leveling sealant. Let it flow; do not overwork. Feather edges with a gloved finger or trowel if needed.
- Protect from foot/vehicle traffic until cured.
1/2 inch or broken edges (repair mortar):
- Brush on concrete bonding agent if required by the mortar manufacturer.
- Mix polymer‑modified repair mortar per instructions.
- Pack in layers, consolidating to remove air pockets. Trowel flush; texture to match.
- Keep shaded and moist cure if the product calls for it.
Sealant geometry (typical)
- Crack/joint width: 1/4–1/2 in
- Sealant depth: 1/4 in (minimum); do not exceed 1/2 in
- Use closed‑cell backer rod sized 25–50% larger than joint width
4) Optional: Resurface for a uniform look
If the driveway is blotchy or pockmarked, apply a polymer‑modified resurfacer over the whole slab after spot repairs. Work in sections with a squeegee and broom finish. This can refresh appearance and seal hairlines.
5) Cure and protect
- Sealant: Skins in 1–4 hours, full cure in 24–72 hours depending on product and weather.
- Repair mortar: Initial set 1–2 hours; restrict vehicles 24–48 hours.
- After 7+ days, apply a penetrating silane/siloxane sealer to reduce water and salt penetration.
Safety tips
- Wear eye, lung, and hearing protection—grinding concrete creates silica dust and high noise.
- Use dust control (vacuum attachment or wet methods). Avoid dry sweeping dust.
- Mind electrical safety with pressure washers and wet surfaces.
- Follow product data sheets for working time and cure.
Best practices and pro tips
- Work in the shade or cooler parts of the day to improve finish and reduce bubbling.
- Cut and clean the crack thoroughly; adhesion fails on dusty or algae‑covered surfaces.
- Use backer rod; it saves material and improves flex performance.
- Tool polyurethane edges lightly to avoid water ponding at the seam.
- For freeze–thaw regions, prioritize flexible sealants in active cracks and seal the driveway annually or biannually.
Common mistakes
- Filling dirty cracks or skipping the routing step—leads to early failure.
- Using silicone or asphalt crack fillers on concrete driveways.
- Overfilling self-leveling sealant so it domes above grade and peels under tires.
- Driving on repairs too soon.
- Ignoring drainage; standing water accelerates cracking and spalling.
When to call a professional
- Vertical displacement across the crack (trip hazard) or a slab that has sunk or heaved.
- Wide, structural cracks that keep growing, or multiple slabs moving—may need slabjacking, foam lifting, or subgrade remediation.
- Severe scaling, widespread map cracking, or exposed aggregate indicating freeze–thaw damage—resurfacing or replacement may be more cost‑effective.
Time estimate: Small DIY crack repairs can be completed in half a day plus cure. Resurfacing a two‑car driveway is typically a full day for two people plus cure. Budget $30–150 for materials for minor repairs; more if resurfacing or renting tools.