Q.: On different occasions, I've been told to wet, moisten, or dampen the subgrade prior to concrete placement. What is the difference between wet, moist, and damp as it pertains to the subgrade?

A.: The American Concrete Institute's Cement and Concrete Terminology (116R-90) defines each term. Wet is defined as "covered with visible free moisture," damp is a "moderate covering of moisture," and moist is "slightly damp but not quite dry to the touch." Thus wet indicates the highest level of moisture and moist indicates the lowest level.

For subgrade preparation, many engineers and contractors use the three terms interchangeably. However, the term wet should not be used. Most specifiers agree that there must be no free water standing on the subgrade, nor should the subgrade have any muddy or soft spots when the concrete is placed. Therefore, damp is probably the best term to use for subgrade preparation.