How to Fix a Cracked Concrete Walkway

A cracked walkway is more than an eyesore — it’s a trip hazard and an entry point for water that accelerates damage with every freeze-thaw cycle. Left alone, a hairline crack becomes a wide gap becomes a heaved slab.

A cracked walkway is more than an eyesore — it’s a trip hazard and an entry point for water that accelerates damage with every freeze-thaw cycle. Left alone, a hairline crack becomes a wide gap becomes a heaved slab. The good news is that concrete walkway repairs are solidly in DIY territory. The materials are affordable, the process is forgiving, and a well-done repair can last a decade before it needs attention again.

This guide covers every scenario: hairline cracks, wide cracks, spalled surfaces, failed control joints, and heave caused by tree roots.

What You Need

The right product depends on the type of damage, but most homeowners will use a crack filler, a resurfacer, and a sealer.

• Polyurethane concrete crack filler (self-leveling) — for control joints and cracks up to 1/2 inch wide
• Concrete resurfacer — thin cement coating applied over the full slab to restore the surface
• Concrete patching mortar — for deeper voids, spalled areas, and edges
• Penetrating concrete sealer — applied after repairs cure to protect the entire slab
• Wire brush and cold chisel — for cleaning out cracks and undercutting edges before patching
• Concrete bonding adhesive — brushed into cracks and repairs to help new material adhere to old concrete

Step 1 — Assess the Damage

Walk the entire length of the walkway and categorize the cracks you find:

Hairline cracks (less than 1/8 inch): These are surface-level and common in older concrete. They are mostly cosmetic but should be sealed to prevent water infiltration.

Medium cracks (1/8 to 1/2 inch): These need to be cleaned out and filled with a flexible crack filler. If there are many of them, a full resurfacing after filling gives the best result.

Wide cracks and open gaps (over 1/2 inch): These often indicate movement in the sub-base. Fill them with patching mortar, but also investigate whether the soil beneath the slab has settled, washed out, or been pushed up by roots.

Control joint failure: The intentional grooves in the walkway have opened up or crumbled at the edges. These need to be cleaned and filled with a flexible joint sealer, never rigid mortar.

Spalling and surface pitting: The top layer of concrete has broken away, exposing aggregate below. This is usually caused by freeze-thaw cycles or deicing salt. A concrete resurfacer addresses this.

Heaved slabs: One slab section is higher than its neighbor due to tree root growth beneath it. This requires a different approach covered in its own section below.

Step 2 — Prepare the Crack

A crack filler applied over a dirty, loose-edged crack will fail quickly. Preparation is 80% of the job.

1. Use a wire brush to scrub out the crack, removing loose material, dirt, and debris. Work the brush along the full length of the crack in both directions.
2. For cracks with crumbling edges, use a cold chisel and hammer to undercut the edges slightly — this means angling the chisel so the crack is slightly wider at the bottom than at the top. This undercut locks the patching material in place.
3. Blow out the crack with compressed air or a shop vacuum to remove all dust and loose particles. Dust prevents bonding.
4. If the crack has any vegetation (moss, small weeds) growing in it, spray with a weed killer and allow to die back, or pull it out mechanically.
5. Rinse the crack with water and allow to dry. Most crack fillers specify whether the crack should be damp or dry — follow the product’s instructions.

Step 3 — Fill Hairline Cracks

For very thin cracks (under 1/8 inch), a brush-applied penetrating sealer or a liquid crack filler is the best approach. These products are thin enough to wick into the crack by capillary action.

Apply the product with a small brush, working it into the crack. Wipe away excess from the surface before it dries. Allow to cure per the label.

For a cosmetic improvement, you can sprinkle a small amount of dry cement over the wet filler and brush it in — this fills the top of the crack so it is less visible after curing.

Step 4 — Fill Medium and Wide Cracks

Self-leveling polyurethane crack filler comes in a caulk tube and is ideal for cracks up to about 1/2 inch wide. It remains flexible after curing, which allows it to move with the concrete through seasonal temperature changes rather than cracking again.

1. If the crack is more than 1/2 inch deep, pack it with foam backer rod first. Backer rod is a compressible foam cylinder that fills the bottom of the crack so you are not wasting filler in a deep void. Cut the rod slightly larger than the crack width and press it in.
2. Cut the tip of the caulk tube at a slight angle to fit the crack width.
3. Apply the filler in a steady bead along the crack, slightly overfilling.
4. For self-leveling products, the material will flow and level itself. For non-self-leveling products, smooth the surface with a putty knife or gloved finger dipped in water.
5. Allow to cure per label directions — usually 24 hours before foot traffic.

For wide cracks over 1/2 inch: Use a vinyl concrete patching mortar mixed to a stiff consistency. Apply bonding adhesive to the crack walls first, then pack the mortar in with a trowel. Overfill slightly and screed level. Allow to cure 24 hours before foot traffic and 72 hours before applying resurfacer or sealer.

Step 5 — Repair Failed Control Joints

Control joints that have opened, crumbled at the edges, or had old rigid filler fall out need to be cleaned and resealed with a flexible product.

1. Use a grinder with a diamond blade, a circular saw with a masonry blade, or a cold chisel to clean up any crumbled edges. The goal is clean, vertical walls on both sides of the joint.
2. Remove all debris and dust.
3. Pack the joint with foam backer rod to the appropriate depth — typically leave 1/4 to 3/8 inch of space above the backer rod for the filler.
4. Apply a self-leveling polyurethane or polyurea joint filler. These products are designed specifically for control joints and remain flexible through temperature extremes.
5. Allow to cure, then tool the surface flush if needed.

Do not use a rigid patching mortar in control joints. It defeats the purpose of the joint entirely and guarantees the concrete will crack adjacent to the repaired area within a year or two.

Step 6 — Resurface a Badly Cracked or Spalled Walkway

When the walkway has many small cracks, surface pitting, or delamination throughout, filling individual cracks is not practical. A concrete resurfacer is the right solution — it’s a thin layer of Portland cement-based material that bonds to the existing concrete and creates a fresh, smooth surface.

1. Fill any cracks wider than 1/4 inch with crack filler or mortar and allow to cure before resurfacing.
2. Clean the entire slab thoroughly with a pressure washer to remove dirt, oil, and any laitance (the weak surface layer).
3. Mix the resurfacer per the manufacturer’s instructions. Most products mix with water to a consistency similar to pancake batter.
4. Pre-wet the slab so it is damp but not puddled.
5. Pour the resurfacer onto the slab and spread with a long-handled squeegee or a concrete float. Work in sections and maintain a wet edge.
6. For a broom finish (recommended for outdoor surfaces), drag a concrete broom across the surface before it sets to add texture and anti-slip grip.
7. Protect from rain, direct sun, and foot traffic for 24 hours. Allow 72 hours before driving any vehicle over it.

Resurfacer layers are thin — typically 1/8 to 1/4 inch — so they do not add structural strength, but they significantly improve appearance and seal the surface from water.

Step 7 — Fixing Tree Root Heave

When a tree root grows under a walkway slab, it lifts one edge, creating a raised lip that is a tripping hazard. You have several options:

Option A — Grind the raised edge (fastest): Use an angle grinder with a diamond cup wheel or hire a concrete grinder to bevel down the raised edge. This removes the trip hazard without addressing the root. The root continues to grow, and the slab will eventually be pushed up too far for grinding to help.

Option B — Remove the slab section and cut the root: Break out the affected slab section with a jackhammer or rented electric demolition hammer. Expose the root and cut it back, then fill the void with compacted gravel sub-base and pour new concrete. This is more involved but is the permanent solution.

Option C — Mudjacking or foam leveling: A contractor injects grout (mudjacking) or expanding polyurethane foam beneath the sunken side of the walkway to level the slabs. This works when one slab has sunk rather than been pushed up.

After any root repair, seal all control joints and the perimeter of the slab to slow future root infiltration.

Step 8 — Apply Concrete Sealer

Once all repairs have cured — at minimum 24 hours, 72 hours is better — apply a penetrating concrete sealer to the entire walkway.

A penetrating sealer (silane or siloxane-based) soaks into the concrete and repels water from within rather than forming a film on the surface. This is the preferred type for outdoor walkways because it doesn’t create a slippery film and won’t peel. Apply with a pump sprayer and spread with a paint roller or squeegee. Wipe away puddles so the sealer doesn’t dry in excess on the surface.

Reapply the sealer every 3 to 5 years, or when water no longer beads on the surface.

Long-Term Maintenance

A well-maintained concrete walkway can last 30 to 50 years. Keep it in good shape with these habits:

• Avoid deicing salts — they accelerate concrete spalling dramatically. Use sand or cat litter for traction in winter instead.
• Reseal every 3 to 5 years to block water infiltration.
• Re-fill control joints when you see the filler starting to crack or pull away.
• Trim trees that are within 10 feet of the walkway and monitor for early signs of root heave.

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