Flaking Concrete Spalling of a thin surface layer early in a slab’s life usually means the finisher troweled bleed water back into the cement paste on top of the slab and sealed the slab surface, trapping water beneath a brittle top skin, and setting up a weak layer between the surface and the base.
Wait For It Timing is tricky for finish troweling. The sheen of standing water should be gone, but the cement still needs to be soft enough to show a bootprint—barely. In hot weather, chill the mix water and fog the area so water can react with cement, not just evaporate. In early troweling, use a wood trowel that opens up the concrete surface, not a titanium trowel that will seal it.
Prep, Clean, and Patch For a durable repair, remove all the soft or loose surface by chipping, wire brushing, or grinding and sand-blasting. Then clean thoroughly with specialty detergent, and apply a specially formulated, acrylic-modified patching and resurfacing compound. Follow manufacturer instructions for best results.