Gravelboy ballast application tool for OO/HO gauge (Mini Auto ballaster) Place on the track and fill with ballast pull smoothly along and the ballast is placed neatly between the sleepers and evenly alone the track side. The built in brushes sweep off the residue on the sleepers this leaves a great finish. All that is need after application is to lightly spray the ballast with some water with a couple of drops of washing-up liquid. Then apply a 50/50 PVA glue water mix this can be sprayed or dripped on to the ballast. These gravel boys come in a number of gauges from Z to O.