You can level an existing concrete floor with a leveling layer of new concrete but you must prepare the old concrete floor first.
How to level concrete slab against a wall.
Whether you want to refinish an uneven basement floor or replace or add new flooring on top of an existing concrete floor somewhere in your home you most likely will need to level the concrete floor.
Neglecting to prepare the old surface will prevent the new concrete from adhering correctly resulting in a weak bond between the two layers.
An even concrete slab is very important if you plan to build anything on your slab or lay down any type of outdoor tile.
Pour and level the concrete.
Uneven exterior concrete slabs should be repaired for reasons of both convenience and safety.
Drag a straight 2x4 screed board across the top of the concrete forms to level the concrete.
Have a helper add or remove concrete in front of the screed as you pull it.
An exterior wall must be placed on the outside edge of the slab so the exterior siding laps down and over the edge of the slab.
You can purchase concrete leveling compounds at home improvement retailers to level out the floor.
Exterior wall on slab must be out on the edge.
Make sure you have enough concrete to fill the entire area to the depth you desire.
Pour concrete onto the existing slab until it is around where you want the final level to be.
Consider a wood shed floor treated lumber joists and plywood.
This prevents water from leaking under the bottom of the wall to the inside of the building.