In this video, This Old House landscape contractor Roger Cook shows how to lift a sinking concrete slab.
1. Cut through slab with gas-powered saw fitted with 12-inch diamond blade; that'll allow the sunken slab to lift up.
2. Use diamond-tipped core drill to bore several large-diameter holes through slab.
3. Use a pneumatic rock hammer to drill a 12-inch-deep hole through each core hole.
4. In a mobile mixer, blend a grout mixture of sand, silt and Portland cement; mix the grout with water in auger.
5. Use a hydraulic concrete pump to pump the grout through the core-drill holes.
6. Continue to pump grout into the holes a little at a time until slab starts to rise up.
7. Once the slab is level, cement the concrete-core plugs back into holes.
8. Push the plugs flush with the slab, then use sponge to clean the area around the plugs.