How to Fix a Collapsing Concrete Floor

Position the tip of a chisel against loose or crumbling concrete and tap it gently with a hammer to break it free from the hole in the floor. Repeat this process all along the floor hole. Undercut the sides of the hole in the floor and level the base of the hole so you have a clean, square or rectangular hole that you need to patch.

Brush away loose concrete, dirt and debris from the hole in the concrete floor. Spray the hole with a hose to remove accumulated dirt, then leave it to dry. Although the hole can remain moist, you have to remove accumulated water from it.

Apply a thin coat of the concrete bonding agent to the inner surfaces of the hole using a small paintbrush. Follow label directions for the application rates and disposal of the bonding agent.

Prepare dry patching concrete in a bucket according to label directions. Be sure to prepare the concrete before the bonding agent is completely dry.

Scoop up a small amount of concrete from the bucket with a trowel and spread it over the base of the hole. Push the concrete into the holes and against the edges of the hole. Repeat this process to fill the concrete floor fully, leaving a small mound at the top that you will level later even with the surrounding floor surface.

Smooth the top of the concrete patch with the edge of a trowel or a flat-edged board. Sweep the trowel or board along the top of the patched concrete, removing the excess. Gently press the top of the exposed concrete surface. Allow it to cure for the time specified on the labels directions.