I received an email today, an edited version of which follows:
Dear Mr. Goss,
I have your book and I have been trying to read, research, and experiment as much as I can before I start in my quest of creating sculptures using concrete. During my research I came across an amazing artist named Mike Moran who uses a technique that makes the concrete look like clay (http://www.anewleafgallery.com/Artist-Detail.cfm?ArtistsID=67). There is nothing out there that explains how to get this look on concrete and there is no way that I can get that look experimenting. By any chance do you happen to know how it is done?
This is what I replied:
Thank you so much for telling me about this artist. The work is really amazing. But to your questions...
The simplest answer is that this artist has obviously been working in concrete for some time and understands its qualities and limitations. I'm sure you could get the same effects, but it takes time and lots of practice. I wouldn't worry too much about mixes and recipes–the main issue is understanding the qualities of the material. These pieces weren't done in the same way that you would work with clay. The armatures are carefully worked out; there is probably steel mesh wrapped around the steel rods so that the concrete is given support while it is applied. You cannot get these kind of forms in concrete without that steel structure underneath. You can make concrete more clay-like by adding fibers and pozzolans (e.g. metakaolin, as I described in the book), but it never becomes as malleable and sticky as clay. You have to learn to work within those limitations.
If you look at the clay head pieces as an example–
The gallery describes it: "With very expressive features, this large head appears to rise out of the ground or table top. Moran etched, burnished, and stained the concrete to convey the illusion of weathered clay." As the description says, it's trying to look like clay, but that's an illusion. My best guess is that the head was basically made around steel mesh, from a fairly stiff grey sand/cement mix. Then thinner layers of black-dyed mix were applied by hand (you can see the marks of some of his tools). It looks as if he's using a fairly stiff mix and really pushing it hard against the surface. When it's partially set, he may be scraping some of that off, burnishing it with wood or steel tools, or rough sanding it a bit, then adding a slightly different tinted mix. The white Portland cement (or maybe that's even paint?) appears to have been added last.
As I've implied, this works looks easy—just as an experienced clay artist can make working with clay look easy. But it's not. It looks easy because he's had lots of experience understanding the material and is at ease with the material. I think one of the signs of what we call good art is that it appears to be effortless. But it can only be effortless when the materials are mastered.
I wouldn't worry about doing more research into concrete before starting. My advice would be to just start, and keep doing it, working through the failures until you develop this ease. I know you asked a technical question, and in a sense I've answered from another direction, but I hope it helps.