Take these steps to make sure your concrete slab is solid, smooth, and level before you start the job.
It's easy to mortar a concrete patio or walkway that is solid, smooth, and level. If you plan to mortar your present slab, check its condition before you start the job.
First check for large cracks and sagging sections. If you find such conditions, the base is not adequate -- you'll need to remove the slab and pour a new one.
Even if your present slab appears to be good, you need to make sure it will stay that way. Dig along the perimeter of the slab and look for a 4-inch gravel base and 3 to 4 inches of concrete. If an adequate subbase is present, check the surface for drainage. A slab must slope at least 1 inch for every 4 feet and should not contain spots higher than 1/8 inch in 10 feet.
A surface crowned in the center for drainage will work as long as the crowning is gradual. You can repair minor holes or flaking with the techniques shown.
30 to 45 minutes per square yard
Repair surface: level, hammer, cold chisel, trowels, grinder, vacuum cleaner, sanding block, brush
Repair structural defects: sledgehammer, crowbar, wheelbarrow, rented concrete saw or jackhammer
Leveling, troweling, grinding
Repair surface: hydraulic cement, thinset, self-leveling compound
Repair structural defects: gravel, reinforcing wire, epoxy bonding agent, concrete mix, 2x4 lumber
To fill depressions in the slab, pour a small amount of self-leveling compound into the depression or trowel on a skim coat of thinset. Add thinset or compound until the surface is level. If you're using thinset, feather the edges even with the floor. Self-leveling compound will do this on its own.