How to Repair Spalled or Cracked Concrete
Restore pitted, cracked, or chipped concrete surfaces using bonding adhesive and polymer-modified patching compound to create a durable, flush finish.
- Read the tools, materials, safety notes, and steps below for free.
- Tap Start Camera Coach when you want hands-free voice help.
- Allow camera and microphone. Point your phone at the work; the coach watches your progress and tells you the next step.
🧰 Required Tools & Equipment
- ✓ Cold chisel
- ✓ Hand sledge or ball-peen hammer
- ✓ Wire brush
- ✓ Shop vacuum
- ✓ Margin trowel
- ✓ Mixing bucket
- ✓ Spray bottle
📦 Materials & Supplies
- ✓ Polymer-modified concrete patch
- ✓ Liquid concrete bonding agent
- ✓ Clean water
⚠️ Safety Checkpoints & Warnings
- • Wear safety goggles while chiseling to prevent concrete chips from striking eyes.
- • Wear heavy nitrile or rubber gloves; wet concrete contains alkaline Portland cement that causes chemical burns.
- • Wear an N95 dust mask when dry-mixing or vacuuming silica dust.
📋 Step-by-Step Guide (6 Steps)
Chisel Out Loose and Spalled Concrete
Hold the cold chisel at a 45-degree angle along cracked and flaking areas and strike firmly with the hand sledge. Undercut the perimeter edges slightly so the bottom of the repair area is wider than the surface opening. Remove all loose, chalky, or crumbling concrete until you hit solid aggregate.
- • All fractured, loose concrete is removed
- • Patch perimeter has vertical or slightly undercut edges rather than feathered taper
- • Leaving feathered (tapered) edges at the break line which will crack and flake easily.
Wire Brush and Vacuum the Cavity
Scrub the entire recessed area vigorously with a stiff wire brush to dislodge hidden micro-fractures and surface dust. Use a shop vacuum to extract all loosened sand, grit, and dust from every crevice. Wipe the area with a damp rag or blast with clean air if micro-dust persists.
- • Bare, clean aggregate exposed with zero loose sand in the recess
- • Dry base shows no residual grey powder when touched with a finger
- • Relying only on sweeping with a broom, leaving micro-dust that acts as a bond breaker.
Apply Concrete Bonding Adhesive
Mist the dry concrete void lightly with clean water so it is damp but without standing puddles. Brush an undiluted coat of liquid concrete bonding agent across the entire cavity, paying close attention to the undercut edges. Allow it to get tacky according to product directions before placing the patch.
- • Surface has a uniform milky sheen with no dry spots
- • Base is tacky to the touch without standing puddles of liquid
- • Applying patch over bone-dry concrete, which leeches water out of the patch prematurely.
Mix the Patching Compound
Pour the required amount of dry polymer-modified patch into a clean bucket. Add water incrementally while stirring with your margin trowel until the mix reaches a stiff, peanut-butter consistency. Mix only the amount you can place within 15 minutes.
- • Uniform grey paste that holds its shape on the trowel without slumping or running
- • No dry powder pockets at the bottom of the bucket
- • Adding too much water, which severely weakens the cured strength and causes shrinkage cracking.
Pack and Press the Repair Mortar
Scoop workable mortar onto the margin trowel and press it firmly into the deepest sections of the repair void. Pack the material aggressively into corners and undercut edges to eliminate air voids. Overfill the repair area slightly above the surrounding slab level.
- • Void is completely filled with compound slightly bulging above surrounding slab
- • No visible gaps or air pockets along perimeter edges
- • Gently smoothing over the top without pressing hard into deep corners, leaving hollow pockets beneath.
Screed, Float, and Match Surface Texture
Hold the flat blade of the margin trowel flush against the surrounding concrete and drag it across the patch in a sawing motion to shave off excess material. Blend the perimeter edges tightly to the existing concrete. When the sheen fades (5-10 minutes), gently drag a damp sponge or stiff-bristle brush across the patch to match the surrounding concrete texture.
- • Patch is completely flush with adjacent concrete
- • Surface texture mimics surrounding concrete without a shiny ring around the perimeter
- • Troweling too long while it sets, which draws water to the top and creates a weak, powdery surface.
Credit: inspired by an original tutorial by Everyday Home Repairs — watch the original on YouTube.
Don’t have everything?
- No Hand sledge? Heavy claw hammer (strike chisel squarely)
- No Margin trowel? Stiff metal putty knife or flat masonry trowel
- No Liquid concrete bonding agent? PVA glue diluted 1:1 with water (for interior dry areas only)