How to Fill & Level Cracks in Concrete

Concrete cracks can be repaired.

All concrete slabs may form cracks over time. The cracks are caused by the ground settling underneath the slab. This settling begins with small hairline cracks, which then turn into larger cracks if the problem is not treated quickly. Moisture, in the form of rain and snow, works its way into the cracks and slowly erodes the hard concrete surface. Vehicle traffic accelerates the growth of the crack. Caught soon enough, a basic repair to the crack will prevent it from getting larger.

Things You'll Need

• Wire brush
• Hair dryer (optional)
• Concrete caulk
• Rag
• Hammer
• Cold chisel
• Broom
• Garden hose
• Concrete patch material
• Plastic bucket
• Hand trowel
• Sheet plastic

Instructions

Hair-Line Cracks

1. Brush away all loose material from the area with a wire brush.

2. Dry the crack thoroughly with a hair dryer or leave to air dry on its own.

3. Apply a concrete patching caulk according to the label directions. Force the caulk into the hairline fissure.

4. Smooth and level the wet caulk with a wet rag. Work the material into the crack with the surface of the rag. Clean the surrounding area of excess caulk.

5. Keep all traffic from the repair until the caulk material has thoroughly cured according to label directions.

Larger Cracks

1. Enlarge and clean out the crack of all debris using a hammer and cold chisel. Hold the sharp end of the cold chisel near the edge of the crack and strike it with the hammer to smooth the edge. If possible, undercut a larger crack so the patch material has a greater surface area for adherence. In many cases, it may be necessary to increase the depth of the crack to a full inch with a cold chisel.

2. Remove all large debris with a broom. Wash out the crack and the surrounding area with a garden hose and a good stream of water. A clean concrete surface will bond better with the patch material.

3. Mix the concrete patch material according to the label directions in the plastic bucket.

4. Fill the crack with the concrete patch material. Use the hand trowel to work the mixture into the crevices of the crack. Smooth the surface of the patch with the flat edge of the hand trowel. Level the material so it is even with both sides of the existing concrete.

5. Cover the patch with a sheet of plastic to retain moisture and increase the strength of the concrete patch. Keep all vehicle and foot traffic from the area until it is thoroughly cured according to label directions. Some mixture may take as much as five days to become fully cured, depending on environmental conditions.

Tips & Warnings

• A good do-it-yourself concrete patch mixture is one part Portland cement to two and a half parts fine sand. Add water and mix to a consistency of thick cake batter. Keep the crack moist when filling. Lift the plastic once a day to moisten the patch mixture. Curing time is at least five days.

• Do not attempt to patch the concrete surface if temperatures are below freezing. Some concrete patch materials may require temperatures above 50 degrees F for a full cure. Consult label directions for product cure rates.

References

• Inspectapedia: How to Evaluate Cracks in Poured Concrete Slabs & Floors
• Aubuchon Hardware: How to Repair Concrete
• Dummies.com: How to Fill Small Cracks in Concrete