Q: I've heard that it's not a good idea to use a steel-trowel finish for air-entrained exterior flatwork. However, I can't find any references that specifically recommend avoiding this practice.

A.: ACI 330R-92, Guide for Design and Construction of Concrete Parking Lots, section 4.5.2, recommends leveling air-entrained concrete with a bull float or scraping straightedge immediately after strike-off, then dragging wet burlap over the surface as soon as the concrete has set enough to maintain a texture. The section further states: "The use of hand or power floats and trowels is not necessary and is not recommended, as their use may result in scaling."The most recent edition of the Portland Cement Association's

Cement Mason's Guide contains the following statements:

  • Because of the danger of scaling or blistering, troweling of air-entrained exterior flatwork is not recommended.
  • Don't hard trowel air-entrained concrete surfaces that will be exposed to freezing and thawing, deicing agents or both.