What Is Top-Cast Finish Concrete?

Summary:

Cesar explains top-cast as a more controlled route to an exposed-aggregate look. Where a traditional exposed finish is achieved by washing the surface, with results that depend heavily on timing and technique, top-cast uses a surface retarder applied to the fresh concrete. The retarder holds the very top layer from hardening at the same rate as the slab beneath it, and that layer is then removed. Because the depth is controlled by the retarder rather than by how aggressively the surface is washed, the exposure comes out more even across the whole area and is typically shallower and tighter than a full wash produces. Homeowners who want aggregate texture without the heavier look tend to prefer it.

Answer:

Top-cast is a way of getting to an exposed look, but with a lot more control over how it comes out. With traditional exposed aggregate you're washing the surface to open up the stone, and how much stone you end up seeing depends on timing and on how that wash goes. Top-cast uses a surface retarder instead. The retarder holds back that very top layer from hardening at the same rate as the rest of the slab, and then we remove that layer. Because you're controlling how deep it goes with the retarder instead of with a pressure washer, you get a more even result from one end of the slab to the other, and usually a shallower, tighter exposure than a full wash gives you. The finish reads more uniform. People who want the texture of aggregate but don't want that heavy, chunky look tend to go this direction. It's a finish that rewards experience, because the timing and the removal are what make it consistent.