Decorative problem clinic

Concrete Construction, June, 2004

Q. I am planning to replace my driveway this spring and would like to know if there are durability and maintenance issues with an exposed aggregate surface as opposed to your basic concrete. I live in the Richmond, Va., area. Thanks for your help!

A. There is no reason related to that product why you should have durability problems. We would recommend that you choose a contractor who has performed this work numerous times in the past. Ask for references to past work and go see them.

One of the tricky things about installing exposed aggregate pavement is getting the right depth of exposure, plus getting an "even" appearance throughout the pavement. If a contractor reveals too much of a stone, it won't have adequate bond and can break loose from the slab. There are two ways to reveal the aggregate: by washing the surface with water as the concrete is getting hard and by spraying the surface with a retarding agent and waiting until the next day to reveal. The second method is the safer approach in our view because only the surface paste is retarded. The concrete below gets very hard and makes a strong attachment to the stones. The depth of reveal tends to be controlled in the process, too.

Air entrainment is the primary durability issue. Your contractor needs to be sure that his mix design has adequate air entrainment in it. This is an issue for all kinds of exterior pavements--not just exposed aggregate.