Concrete foundations, concrete driveways and sidewalks, concrete walls and other things concrete occasionally need repair. This Fix-It Guide on concrete repair tells how concrete works, what often goes wrong, how to identify a concrete problem, and what parts and tools you will need to fix it. It then gives simple step-by-step instructions for how to fill a crack in concrete, how to patch a concrete block, how to replace a concrete block, and how to fix a water leak in a concrete-block basement wall.
How Does Concrete Work?
Concrete is a composite material made up of a binder (Portland cement), aggregates (small rock chips), and water. Once mixed, it’s spread into an area with perimeter forms, then allowed to dry solid. Once dry it is as hard and strong as stone. Concrete is used for building foundations and slabs, garage floors, driveways, sidewalks, fences, and many other uses. It is also the major component in concrete building blocks.
What Can Go Wrong with Concrete?
Concrete can crack, chip, erode, and break. Most damage is caused by water and weather–though earthquakes can also have an adverse effect.
How Can I Identify a Concrete Problem?
- If a concrete block is chipped, you can patch it (see below).
- If a concrete block is damaged beyond repair, you can replace it (see below).
- If a concrete-block basement wall leaks, you can seal it (see below).
- If a concrete driveway, sidewalk, garage floor, wall, or other concrete surface is cracked, you can fill the crack (see below).
Oil, if left standing, can chemically damage and weaken the concrete. Use sand to soak up patches of oil on concrete. Then clean the area with mineral spirits or a de-greasing solution.
What Do I Need for Concrete Repair?
- Cold chisel
- Mason’s trowel
- Small sledgehammer
- Wire brush
- Work gloves
- Cement patch
- Jointing tool
- Striking tool
- Mortar box
- Power drill with masonry bit
- Safety goggles
- Vacuum cleaner
- Hydraulic cement patch
- Small broom (whisk broom)
- Paint brush
- Concrete repair caulk
- Masking tape
- Bonding adhesive
- Vinyl-reinforced patching compound
What Are the Steps to Concrete Repair?
Fill a small crack in concrete:
- Clean out dirt and debris with a small broom.
- Apply concrete repair caulk as a temporary repair until you can make a better repair with concrete patch.
Repair concrete cracks as soon as you find them so they don’t continue to enlarge.
Fill a larger crack in concrete:
- Clear out loose debris with a metal chisel.
- As needed, attach a board to contain the new concrete. Also use a board or masking tape to protect adjacent surfaces as needed.
- Apply a thin layer of bonding adhesive.
- Fill the area with cement patch in thin layers as directed by the manufacturer.
Patch a concrete block:
- Remove loose material from the block with a chisel and a wire brush.
- Spread the cement patch in to the hole in layers using a trowel.
- Smooth the surface of the patching material with a mason’s trowel and allow to dry.
Replace a concrete block:
- Use a chisel or power drill with a masonry bit to remove the block beginning at the center.
- Use a chisel and hammer to break up and remove remaining mortar.
- Spread a bed of mortar in the lowest portion of the hole.
- Spread mortar on the other three sides of the block.
- Insert the new block in position in the hole, carefully aligning it to be flush at the front edge.
- Use a striking tool to make the mortar conform to neighboring blocks.
Fix a water leak in a concrete-block basement wall:
- Remove loose mortar and dirt from the wall using a wire brush and shop vacuum.
- Remove loose concrete around cracks and small holes.
- Apply hydraulic cement patch to the damaged area following the manufacturer’s directions.
- Use a mason’s trowel or a jointing tool to finish installing the patch and allow it to dry.