Level A Concrete Floor. It levels the whole concrete slab, not just the surface. An underlayment is a thin layer of material sandwiched between two other materials. Slip shims under the low end of the 2x4 rail until it's perfectly level, then use a scribing tool to transfer the unevenness of the floor onto the rail.
This would work out to about $800 for a 20'x20′ garage. They can correct uneven floors, repair damaged concrete, and provide a smooth and durable new surface for decorative treatments. The product is mixed with water, pumped or poured into place and spread evenly with a gauge rake.
Gallery of Level A Concrete Floor
The latex stops it from cracking because your levelling compound will be about 1/2 inch thick, but depends on the condition of your 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. Use your thumb or fingers to pack it in tightly for it to cure properly and hold its shape as you go along. Apply from featheredge to 2 in.