Concrete is a durable construction material and has many uses around a house. Masons pour concrete for driveways, sidewalks, foundations, patios and slabs. Adding a new layer of concrete can hide old concrete damage as long as the damage is not severe. Lifting, gaping cracks and large holes require concrete removal. Pouring new concrete over badly damage concrete will yield substandard results.
Grind the surface of the concrete slab with a masonry grinder to remove the top layer and rough up the surface.
Sweep away dust and debris from the surface of the slab.
Drill 3/8-inch holes 2-inches deep with a power drill equipped with a carbide masonry drill bit every 6-to-8 inches across the entire slab surface. If you are using thicker rebar, drill holes to accommodate the size of the rebar.
Cut rebar into 3-inch sections with a circular saw equipped with a carbide blade. Cut enough pieces to fill all of the drilled holes.
Vacuum the holes with a shop vacuum to remove the dust and debris from the holes.
Paint the inside of the holes with an epoxy-based concrete binding agent. Hammer the rebar into each hole with a heavyweight masonry hammer. The rebar will stick up above the surface of the slab 1-inch.
Set up forms around the existing slab with 1-by-6 lumber. The forms must stand a minimum of 2-inches higher than the surface of the slab. Position the lumber on the 1-inch side with the 6-inch side standing up. Get a close as possible to the edge of the slab without encroaching on it. Drive stakes into the ground behind the forms to hold the forms in place firmly.
Mix concrete with water in a large trough or call a ready mix concrete company for a delivery. For a large concrete pour, a ready-mix delivery is a better choice than hand mixing.
Apply a coat of epoxy-based concrete bonding agent over the entire surface of the slab with a long-handled masonry roller.
Pour a minimum of 2-inches of concrete over the wet epoxy. Spread the concrete evenly throughout the forms with the flat side of a metal rake.
Drag a long board over the surface of the new concrete to smooth and level it.
Knock down hills or fill in valleys by dragging a darby over the concrete. A darby is a long masonry tool with a handle, used to level the surface.
Apply curing compound to the surface or spray the concrete with a misting of plain water every day for seven days and tarp the new pour until it is set.
Wear safety glasses, gloves and a dust mask when working with concrete.