Delaminations are separations of thin layers of the slab surface from the base concrete. Delamination typically results in break off of surface layers, 1/8 to ¼ inch in thickness, from a finished slab. These are primarily caused when the concrete mixture and construction conditions result in premature or excessive finishing whereby the slab surface is densified and traps air and bleed water beneath the densified layer. Delaminations can vary in size from a few square inches to many square feet. Delaminations are similar to blisters, but much larger.

Delaminations are more commonly seen in hard-troweled floor slabs and occur if final troweling is performed when the surface appears to have stiffened sufficiently but concrete is continuing to bleed. Delaminations can also occur with other finishing methods with excessive and premature finishing that densifies the surface. Corrosion of reinforcing steel near the concrete surface or poor bond between two-course placements may also cause delaminations (or spalling). These typically result in thicker surface separations.

• Avoid placing concrete directly on vapor retarders or impermeable subgrade, if the application allows
• Do not use air-entrained concrete for slabs that will receive a trowel finish
• Avoid placing concrete on substrate with a temperature of less than 40°F (4°C)

• Do not over consolidate and seal surface early—before air or bleed water from below have escaped
• Avoid dry shakes on air-entrained concrete
• Use higher temperature concrete or accelerating admixtures to promote even setting throughout slab depth