How Can I Raise Up the Side of a Sunken Cement Slab?

Clean the surface of the cement slab with a broom to remove accumulated dirt and debris. Place a straightedge or level on the surface of the slab to determine which side is sinking, and how high it needs to be brought up to the required level.

Drill 1 1/2- to 2-inch-wide holes through the sunken section of the slab using a core drill. Bore these holes every 3 to 8 feet along the sunken slab, depending on its size. Ensure the holes are 12 inches inwards from the edge of the slab.

Use a rock hammer to form a 12-inch-deep hole through each core hole.

Prepare the grout mixture for the holes by mixing fly ash, Portland cement, sand and water until you achieve a mortar-like consistency.

Add the prepared grout into each hole along the sunken side of the cement slab using a hydraulic concrete pump. Insert the pump’s hose into a hole and pump the grout into it, maintaining a consistent pressure between 50 and 100 pounds per square inch. The pressure gauge on the pump signals the pressure.

Continue to pump the grout into the hole until the sunken section of the cement slab gradually begins to rise. Remove the hose from the hole when it is completely full and insert it into the adjacent 12-inch hole. Repeat the process to pump the grout mix into it until the slab rises.

Lay a level or straightedge over the top of the slab and check whether it is even. If required, pump more grout into the holes so the sunken side is level with the remaining cement slab.

Cap the holes with mortar. Press the mortar down to remove trapped air bubbles, and wipe off excess from the tip with a trowel. This ensures the top of the mortar plugs are level with the surrounding cement slab.