In the past I have used various plaster products as well as Durham’s Water Putty with varying degrees of success. The problem I always had is they all would harden before I was able to get the roads completely smooth and I would be forced to sand down the high spots and fill in the voids.
I got the idea of using tile grout watching a how-to video. A half hour after applying the grout, the excess could still be cleaned up with a damp sponge. That seemed to indicate it would still be workable for at least a half hour so it would give me a better chance to smooth it before it hardened.
I purchased two types of grout. One was a tub of premixed vinyl grout and the other was a bag of powdered grout that had to be mixed with water. I opted for the vinyl grout which had the added advantage of being pre-colored. I bought this at Lowe’s and the color was slate gray.
After making the forms for my city streets, I began filling the forms with the grout and tried to spread it using a 5 inch wide putty knife. It quickly became apparent that it was too thick to spread smoothly so I thinned it out with a small amount of water. It didn’t take much water to get it to the consistency of pancake batter. After doing one street I waited for a half hour to do the smoothing but because of the added water, it was requiring longer for it to dry enough for this step. I had done this late at night and didn’t want stay up until it was ready to be smoothed. By morning it had hardened much like plaster or water putty would have done. I had to sand down the high spots and fill in the voids with thinned grout. I ended up with fairly smooth streets with a slightly gritty texture. The color was a medium gray which I think is just about right as the base color for asphalt roads. I’ll use various weathering powders for finish as I always have.
For the subsequent streets I thinned the grout ahead of time. This should be done sparingly as a little water goes a long way toward getting th