Patch all cracks, crevices, and holes in the old concrete surface. For hairline cracks up to 1/8 inch wide, mix four parts of Ardex Concrete Dressing to one part water. Force the thick paste into the cracks with a putty knife. For larger cracks up to 1/2 inch wide, use concrete-repair caulk. Squeeze the caulk into the cracks with a caulking gun, and smooth it with a putty knife.