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Scaling concrete surfaces

Surface flaking and peeling caused by freeze-thaw cycles, deicing salts, or insufficient curing.

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When concrete scales from freezing and thawing, the finished surface flakes or peels off. It generally starts as localised small patches which later merge to expose large areas. Light scaling does not expose the coarse aggregate. Moderate scaling exposes the aggregate and may involve loss of up to 3/8 inch of surface mortar. In severe scaling, more surface has been lost and the aggregate is clearly exposed and stands out.

Concrete slabs exposed to freezing and thawing in the presence of moisture and/or deicing salts are susceptible to scaling. Most scaling is caused by:

  • Use of non-entrained concrete or too little entrained air.
  • Application of calcium or sodium chloride deicing salts. Ammonium sulfate or ammonium nitrate can cause scaling as well as severe chemical attack.
  • Any finishing operation performed while bleed water is on the surface: this produces a high water-cement ratio and therefore a weak surface layer.
  • Insufficient or no curing: often results in a weak surface skin that will scale when exposed to freezing and thawing.

Use air-entrained concrete: severe exposures require 6–7% air content; moderate exposures 4–6%. Do not use deicing salts such as calcium or sodium chloride on new or recently placed concrete; use clean sand for traction. Never use ammonium sulfate or ammonium nitrate as a deicer.

Provide proper curing using a liquid membrane curing compound. Do not perform any finishing operations with water present on the surface. Protect concrete from the harsh winter environment by sealing with a 50/50 mixture of boiled linseed oil and mineral spirits. Late summer is the ideal time for surface treatment.

The repaired surface will only be as strong as the base surface to which it is bonded. The surface must be free of dirt, oil or paint and must be sound. Use a hammer and chisel, sandblasting or jackhammer to remove all weak or unsound material. The clean, rough textured surface is then ready for thin bonded resurfacing:

  • Portland cement concrete resurfacing
  • Latex modified concrete resurfacing