Some concrete damage runs too deep for patching. If you’re dealing with a section of slab that’s cracked through, crumbling, sunken, or delaminated, a full replacement of that portion is often the best fix. But it has to be done properly — sloppy cuts or poor bonding can lead to more failures down the line. In this guide, we walk you through how to professionally remove and replace a section of a concrete slab, step-by-step.
Start by marking the perimeter of the damaged section using chalk or spray paint. Use a square, level, and straight edge to keep corners tight — jagged edges make formwork and finish work more difficult. Add at least 100 mm of clearance beyond visible damage to ensure you're removing all weak material. Plan your cut so it avoids expansion joints, structural connections, or service conduits if possible.
Use a walk-behind concrete saw with a diamond blade to cut through the slab perimeter. Cut at full depth to create clean, vertical edges. This helps your new concrete bond better and makes the patch easier to trowel flush. Wear full PPE — cutting generates high dust and noise. Score the outline first, then deepen the cut in multiple passes. Avoid overcutting beyond corners to prevent cracks propagating outward.
Use a jackhammer or demolition hammer to break up the cut section into manageable chunks. Start from the center and work outward to avoid damaging surrounding slab edges. If the concrete is thick or reinforced, use pry bars to lift and remove each piece once loosened. Clear the rubble fully and vacuum the base clean. Take care not to damage rebar unless you plan to replace or re-anchor it.
Once removed, inspect the base layer beneath the slab. If the subgrade is loose, wet, or sunken, compact it using a plate compactor and add fresh hardcore or MOT Type 1 as needed. A solid base is crucial for preventing the new section from settling or cracking. Bring the base up to the required level and screed it flat before moving forward.
Drill and epoxy-set dowels into the surrounding slab edges to tie the new pour to the old. Use steel reinforcement mesh or rebar if the slab is structural, load-bearing, or over 100 mm thick. Ensure mesh is raised to mid-depth using chairs or spacers. This reinforcement prevents differential movement between the old and new concrete.
Use timber or plastic forms to contain the new pour if your slab has exposed edges or adjoins soil. Brush bonding agent onto the exposed cut faces of the old concrete — this helps new concrete chemically and mechanically adhere. Use a product suitable for fresh-on-old applications and apply it just before pouring. Avoid pooling or letting it dry out prematurely.
Use a concrete mix that matches the strength and finish of the surrounding slab — typically C25/30 or higher. Pour carefully into the prepared area and compact using a tamping rod or concrete vibrator. Screed flush with the existing slab using a straightedge. Use a float to close the surface, matching the finish texture (broomed, smooth, power floated) as closely as possible.
Use an edging trowel to detail the joint line and help prevent future chipping. Finish the surface using the same method as the rest of the slab. For driveways or patios, that may be a brushed finish for grip. For interiors, a smooth trowelled finish or later polish may be used. The goal is seamless appearance and consistent texture — this is where good tradesmanship shows.
Cover the patch with plastic sheeting or apply a curing compound immediately after finishing. Curing is essential to prevent cracking, surface dusting, and inconsistent colour. Leave curing in place for at least 3–5 days. Once cured, seal the area to match the rest of the slab. Use silane-siloxane sealer for external slabs, or densifiers or resin-based sealers indoors. This protects the repair and blends it visually.
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