Tile grout makes great ballast and roads an stuff like that where you need bare ground or like a desert scene. Apply it dry like you would ballast and use wet water and white glue. Yes it will be hard and noisy. Ever slept within a hunnert yards of the GN mainline out in MT where the trains go by at sixty and blow for the grade crossing. Its noisy all right but after a coupla days you get use to it. The locals don’t even hear it.
An added bonus !! Look at all the colors you can get.!!