Flaking Concrete Spalling of a thin surface layer early in a sla…
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.
Harry Whitver
Wait For It Timing is tricky for finish troweling. The sheen of …
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.
Harry Whitver
Prep, Clean, and Patch For a durable repair, remove all the soft…
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.
Scaling, flaking, or spalling—whatever the name, you see it often in an old garage or driveway slab exposed to freeze-thaw weather and de-icing salts. The top surface of the slab flakes up, revealing coarse gravel aggregate and sometimes even reinforcing mesh or bar. Preventing weather-related spalling requires using air-entrained concrete, curing well, and applying a water-repellent sealer after the slab is cured.
But you occasionally see “delamination” of the slab surface even when there’s no freezing and thawing, early in the slab’s life. Sometimes a “drumming” sound betrays the hollowness under the surface while construction is still ongoing.
In those cases, the cause may be traceable to improper finishing: typically, the finisher hard-troweled the slab surface while bleed water was still trying to escape. The trapped water creates a weak layer between the top surface and the strong slab below. The repair, unfortunately, will be the same as for freeze-thaw damage: chip or grind away the weak surface, clean thoroughly, and patch or re-surface using a polymer-modified cement compound.
