Q.: After the forms have been removed does hand rubbing the surface actually improve the weather resistance of the concrete? Are there other methods that will provide the same amount of protection?

A.: Hand rubbing is done mainly to produce uniform appearance to fill bugholes or overcome blotchiness or unsatisfactory color.

The durability of concrete in freezing and thawing exposures is seldom a problem on vertical surfaces. An adequate air content in the concrete mix can be used to protect against freeze-thaw damage.

Other potential effects of weathering chemical attack by atmospheric pollutants, collection of airborne dirt and dust, nonuniform collection of such contaminants, popouts from certain components or contaminants in the aggregate, staining from certain materials used in or with concrete, efflorescence, and cracking or spalling from building movements ,are special problems requiring other measures. These are discussed in a series of three articles, "The Weathering of Concrete,""Designing of Concrete for Weathering" and "Constructing Concrete for Weathering," which appeared in the January, February and March 1972 issues of Concrete Construction.