Okay I am going out on a limb here for the challenge build. So far for the indoor my rocks have consisted of carved foam only. In HO and in N I used foam bases (among other things) and glued on plaster cast rocks which I made using latex rubber molds. I was all set to make some plaster castings of basalt columns using latex molds I made from masters my friend Dick Whitney made. I have the molds all made up, there are three masters and I made a mold of each. I just figured I would do what I have always done and cast them in white plaster and paint them. Then I was lying awake in the middle of the night thinking about this and started thinking about how to dye plaster. It would sure be nice to start with a black or very dark grey base. This led to powdered concrete dye which then led to the big bag of black sanded grout I had bought at the ReStore last year for a buck. I am, as I am typing, waiting for the first casting made with 100% sanded grout. I am worried it will be very brittle as grout really isn’t very structural. I figure if this fails I will try a combination of say 70-30 or 60-40 plaster to grout. Maybe even add some cellulose insulation for reinforcement if I need to get real crazy. But these are indoor rocks and are small 2-3 inches wide and maybe 5-6" tall so I am not thinking I need a bunch of over the top reinforcement. At 1:24 these will be small basalt columns. I think he was thinking O scale when he made them. But basalt can come in small coulmns as well as giant ones for this I think it will work nicely if I can get a good casting. In all else fails I will just go back to plaster dyed with acrylic paint.
The idea behind the sanded grout is to not only give it color but texture. Basalt is not smooth, it is . . .well kinda sandy feeling. So i am hoping I will achieve a nice looking base rock from which to work with.