To use self-leveling cement, begin by cleaning the concrete floor thoroughly. Remove oily patches or oil stains by allowing sawdust to sit overnight on those areas to absorb any residual oil. Once the floor is clean and oil-free, place rubber threshold strips across door openings to prevent the self-leveling compound from seeping into other rooms. Self-leveling cement creates a completely level concrete floor if properly installed.
Apply surface primer on the clean concrete floor by pouring a small amount of the primer onto the floor and spreading it over the area with a long-handled broom. Do not allow the primer to pool in low areas in the floor. Also, mark any noticeable ridges with a pencil while spreading the primer.
Sand down the ridges in the concrete floor with a power sander after the primer dries completely. Use a Shop-Vac or similar vacuum to remove any resulting dust before proceeding.
Mix self-leveling cement compound according to the manufacturer's instructions, but do not make more compound than you can use in 20 to 30 minutes. Start spreading the compound furthest away from the door. Pour it onto the floor in rows approximately 12 inches wide. After every row, use a concrete spreader to smooth the area so that the compound is approximately 1/4 inch deep. When you run out of compound, feather the end of that row with a trowel to avoid lines.
Mix more compound and continue spreading it until you reach the doorway. Use a trowel to ensure that the compound adequately fills any gaps and meets the rubber threshold. Let the compound cure, then use a power sander to lightly sand the new floor to remove any small imperfections.