Ensuring that concrete flooring is level is critical when you wish to apply floor coverings such as carpet, wood planking, and tile over it. Follow these guidelines to level a slab of concrete flooring inside a room of an existing building, prior to laying a new interior floor.
Step 1 - Empty and Clean the Concrete Floor Area
Remove all furniture, vehicles, boxes, rugs, and other items from the entire area of the concrete floor to be leveled. Sweep the floor area with a heavy-duty broom, picking up dust, hair, and other debris. Vacuum the area well with a heavy-duty shop-vac style vacuum cleaner. Go over the entire floor with a polisher with coarse grit sandpaper attached to the rotating heads, and then vacuum once more to remove the concrete dust.
Step 2 - Find the High and Low Spots in the Concrete Floor
Use a carpenter's framing square and two long pieces of wood planking that you have checked are straight to examine the floor for high and low spots. Mark the high spots with a series of arrows or zigzag lines with a marker or sidewalk chalk. Mark low spots by drawing a series of circles from the outside rim inward to the center.
Step 3 - Grind Down Bumps in the Floor Surface
Obtain a concrete sander on a short-term rental from a building supply center. Use the largest one available to grind down large bumps in the floor surface. Open all the doors and windows enclosing the space where you are grinding. Move the concrete sander slowly and carefully to avoid creating pits in the floor.
Step 4 - Clean and Vacuum the Floor Again
Vacuum the floor surface again, and give it a quick damp-mop with water only to remove any traces of concrete dust. Allow the floor time to dry completely before proceeding.
Step 5 - Prepare the Concrete Floor Leveling Mixture
In a steel or aluminum bucket, prepare the concrete floor leveling mixture according to the instructions. Mix just a small amount each time, as it cures and dries quickly. Fill the low spots in the floor with the mixture, and draw the trowel or wood plank over it to ensure the top edge is level with the rest of the floor. Let the mixture set for 30 minutes then smooth the top edge of the fill spot with the trowel or broad putty knife.
Step 6 - Recheck the Floor After Leveling
Check the success of your leveling operation with the carpenter's framing square and straight planks. Mark and fix any unsatisfactory areas.
Step 7 - Polish the Concrete Floor
Go over the entire floor once more with fine-grit sandpaper, 220 or 300, on the floor polisher. Vacuum the floor again and mop it, ensuring no loose concrete grit or dust remains.