SP standards circa 1908 called for the roof walks to be painted and "sanded". Basically they threw sand on the wet paint to give good footing for the crew who were up there.
This makes good sense. The life expectancy of an unpainted board is really short. Paint, especially the old linseed oil paints which were glossy by nature would make things slippery.
SP also called for sanded paint on the wainscotting of depots. The sand made the paint "tougher" and more likely to survive being bumped by baggage carts and such.