How to Chisel Out a Crack

Cracks are the number one problem with concrete.

Cracks are a common occurrence in materials such as cement and plaster. Shifting foundations often cause cracks found on walls and basement floors. As time passes these cracks get larger if left alone. Simply filling in a crack with the appropriate patching material is only a temporary fix. Professionals can be brought in to repair the problem, but this can be expensive. Professionals know how to properly chisel out a crack which allows a strong joint to be formed when the crack is filled. Use the same techniques to save money on this necessary repair.

Things You'll Need

• Concentrated liquid dish-washing detergent
• Water
• Toothbrush
• Painter's masking tape
• General purpose chisel (1-inch wide blade)
• Mallet with a metal head
• Vacuum (shop vacuum or standard vacuum with a hose attachment)
• Rag
• Utility knife
• 220-grit sandpaper

Instructions

1. Clean the crack thoroughly. Grease and bacteria based deposits mold build up in and around cracks. These deposits prevent the filler from adhering to the crack when repaired. Mix one ounce of liquid dish-washing detergent to two quarts of hot water. Use a toothbrush to scrub the inside and outer edges of the crack. Allow six hours drying time.

2. Examine the crack thoroughly from end to end. Cracks tend to be noticeably larger at the center and taper off to a thread-like width on either end. These hard to notice cracks have to be chiseled out and filled or they will continue to expand, requiring the filling process to be started all over again. Use painter's masking tape to mark off the beginning and end of the crack.

3. Enlarge the crack with a chisel. The crack has to be made deeper and wider in order for the filler to have enough surface area for proper bonding. Fillers, such as cement, work by adhering to the surfaces around them. The larger the bonding surface, the great the adhesion. Create a U-shaped groove in the crack at least a one inch wide. Even if the crack is barely noticeable, it needs to be enlarged to ensure a strong bond. The crack should be enlarged to a depth of one inch. Hold the chisel at a 90-degree angle, firmly tapping the chisel's head with the mallet.

4. Vacuum the crack to remove any remaining debris. Before filling the crack, the area must be absolutely free of any debris that creates a barrier between the cracks surface and the filler. Once, vacuumed, take a moist rag (use hot water only) and thoroughly wipe down the cracks walls and surrounding area. Allow at least six hours drying time. The crack is now ready to be filled.

Tips & Warnings

• If there is any paint in the crack after chiseling, use sandpaper or a utility knife to remove the debris. If the surface around the crack has a gloss or sheen to it, use the sandpaper to remove the coating. Natural cement has a flat finish, while painted or sealed cement has a slight gloss to it. This coating needs to be removed to allow the filler to bond to the crack. This same technique can be applied to repairing cracks in Sheetrock and other building materials, with the omission of the use of soapy water. With Sheetrock, sandpaper is used to clean off any grease or debris followed by vacuuming.

References

• Accurate Building: PDF Download: How to Use a Cold Chisel
• Aubuchon Hardware: How to Repair Concrete
• Olde World: Basic Cement and Concrete Principles and Terminology
• Cement.org: Cement and Concrete Basics