Distinguish surface retarder from curing compound.

• A. Surface retarder slows surface set; curing compound retains moisture for curing
• B. Surface retarder accelerates curing; curing compound dries surface
• C. Surface retarder adds air
• D. Curing compound dissolves cement

Answer: (A)

The key idea is that surface retarders and curing compounds serve opposite roles on the concrete surface. A surface retarder slows the setting of the cement paste right at the surface, creating a workable glaze that you can later wash away to reveal the aggregate or pattern beneath. A curing compound, on the other hand, forms a protective film on the surface to keep moisture in, so the concrete can hydrate properly and gain strength.

So the statement that a surface retarder slows surface set while a curing compound retains moisture for curing captures those distinct functions accurately.

The other descriptions don’t fit how these products work: surface retarders don’t accelerate curing, curing compounds don’t dry the surface, and the ideas about adding air or dissolving cement aren’t correct for these products.