A garage floor that's built to withstand the weight of fully loaded cars and trucks is a strong and durable surface that can withstand most stress without damage. Most garages aren't heated however, which means that the concrete floor is subjected to cycles of extreme temperature variants. Temperature changes, combined with water seepage, can create a condition on your garage floor known as spalling. When the floor spalls, the concrete on the surface flakes or pits severely, creating large patches of loose material that can damage vehicle tires and weaken the slab. Repairing a garage floor experiencing concrete spalling requires the removal and replacement of the damaged material. After the replacement process, the floor will be as strong as before, ready for use for decades to come.
Remove any trim or baseboards surrounding the garage floor. Use a prybar to pull the trim away from the walls, prying it up at the nail locations and then placing the trim aside to reinstall after the repair process.
Remove the concrete flakes from the garage floor. Use a stiff bristled broom to clear away loose flakes and any dirt that's accumulated in the damaged patch of concrete. Cut away partially attached flakes with a cold chisel and hammer. Place the edge of the chisel on the end of the flaked concrete where it joins the slab, then strike the chisel firmly with the hammer to cut through the flake, severing it and leaving healthy concrete behind. Sweep up the severed flakes.
Clean the garage floor, including the cleared flaky area, using a power washer. Open the garage door and beginning at the top of the slab, wash the floor with the power washer pointing the water flow outside of the garage and away from the foundation of the building. Wait for the concrete to dry completely before beginning the patching process.
Place a strip of duct tape bordering the garage floor, covering the edges of any adjoining surfaces to prevent the patching material from spreading beyond the floor itself.
Spread acrylic bonding agent onto the garage floor with a nap roller. Cover the floor completely with a light layer of the whitish bonding material. Use a paintbrush to apply the agent to the spalled area in order to ensure that every inch of the spalled surface is covered. Wait for the agent to cure slightly, turning clear in colour but remaining sticky to the touch. The bonding agent helps the concrete patching material stick to the old concrete and ensures that the patch will move along with the old concrete, preventing cracking or further spalling.
Add water to the concrete patch mix in a large bucket and use an electric drill with a paddle attachment to mix the patch to a thick paste. Pour the concrete patch material into the hole left from the spalled concrete while the bonding agent is still sticky. Use a steel trowel to press the patch material firmly into the hole, filling it completely. Level the patch material with the surrounding concrete surface, smoothing it with the trowel. Stepping on the bonding agent will not remove it from the concrete surface. Wait for water to seep to the top of the patch and then evaporate before continuing.
Mix the self-levelling concrete overlay, adding any colourant while mixing. Pour the overlay across the garage floor, covering the floor completely with a light layer. Spread the overlay using a squeegee. The overlay levels out as it dries. Leave the overlay to dry for the time suggested by the overlay manufacturer.
Remove the protective duct tape from the surrounding surfaces and then reinstall any trim taken from the base of the garage walls.
Protective clothing such as work gloves, long sleeves, safety goggles and a face mask should be worn during the patching process as the materials can cause slight burning on skin, as well as eye and lung irritation.