Just spit balling, and wondering if it would work to use the premixed concrete mix with the biggest stuff screened out as ballast. Maybe thstuff that you don.t even have to mix just spread and wet down???
O a mortar mix and shape it and spread some cat letter on top . Or would the train vibrations break it all up?
O a mortar mix and shape it and spread some cat letter on top . Or would the train vibrations break it all up?