When a concrete slab is uneven, it can create problems. Water will pool in low areas when it rains and furniture will be unsteady when you try to furnish the space. If you plan to lay any type of flooring over a concrete slab, an uneven surface may also cause the floor you lay to crack or warp. Though levelling an uneven concrete slab might seem like a job that takes an expert and heavy-duty equipment, it is actually a fairly basic process that many do-it-yourselfers can handle on their own.
Mark all of the spots in the concrete slab where the surface dips down. Locate the uneven spots by placing a flat wooden 2x4 on the floor, starting in the corner of the room. Shine a flashlight along the side of the board and see if any light gets in. If the floor dips down anywhere below the board and lets light in, mark the spot with chalk. Move around the entire floor surface with the board and mark all the spots.
Remove all of the dirt and dust from the spots in the floor that need to be filled by wiping them with a damp cloth. If you remove your chalk marks while cleaning, mark the spots again.
Add levelling compound to a bucket and consult the directions on the compound to add the correct amount of water. Per Ask the Builder, you shouldn't mix more than a gallon of levelling compound at a time.
Spread the mixed levelling compound over the low areas in the concrete slab until the dip is filled completely. Once filled, drag the edge of the wood board over the filled dip in the concrete to remove any of the levelling compound that sits above the surface of the concrete slab. Use a wet rag to clean the excess compound from the floor before moving on.
Continue to add levelling compound to the slab until all of the low spots are filled. Keep the slab dry and don't let anyone walk on it for 24 hours. After 24 hours, the concrete slab should be dry.