On a parking structure project in the South a 3,000-square- foot area of ramp slab has a wavy surface. The depressions seem to be about 1/4-inch thick. Can a cementitious overlay correct this?
Be cautious about that approach. Our reservations about thin cementitious overlays in exposed traffic applications relate mainly to two factors: successful bonding and the potential for shrinkage cracking. Bond is important for most cementitious overlays and critical for thin ones. If a bond failure occurs, the delaminated overlay may crack and spall under traffic. To develop good bond, extensive surface preparation deep shotblasting, sandblasting, or scarifying may be needed. The surface usually is conditioned with a bonding agent, grout, or paste fraction of the patch material just before applying the repair material. Careful curing is vital to avoid shrinkage cracking. A prolonged moist cure is recommended for cementitious mixes; latex-modified repair materials should be cured in strict accordance with manufacturer recommendations. Before proceeding much further, get a better idea of the depth and extent of waviness. Rather than adding material, you may have more success grinding the high spots.