When an owner decides to use decorative stamped concrete on an exterior slab, they usually have high expectations—a clean stamped pattern, consistent color, and a durable surface. To get a durable surface, normally we would use entrained air in the mix to protect from freeze-thaw damage, although this can create a stickiness in the concrete that makes the stamping process more difficult. As a result, some decorative contractors will specify a lower air content than normal, reasoning that the color hardener creates a more impermeable surface that will resist intrusion from water and deicing salts. And also that a sealer is likely to be applied prior to any danger of freeze-thaw, which will further resist intrusion and prevent the surface from achieving critical saturation.
While all this sounds reasonable, to me any reduction in air content seems dangerous. Water may move more slowly into a color-hardened surface but it will still move and on an exterior slab, the water is coming up from below as well. Freeze-thaw spalled surfaces will completely ruin a beautiful stamping job. On the other hand, experienced decorative contractors know what results in a durable surface. What do you think? Is less air acceptable on a surface with color hardeners?