The damage can be seen in the first image that shows about one quarter of the full board. The white areas are where stones have come off, where epoxy resin or plaster mixtures have been chipped away, or where my children have literally been picking at things. There are several scrapes that have been sustained as well that are less obvious.
To correct these maladies, I use a combination of regular paints (red, brown, black) and a special textured paint (basically a thick brown coloured paint that dries anything but flat). I mix the paints together, but not completely -- i.e. there are still streaks of obvious red in the brown colour for instance and apply this liberally to the affected areas. The result is below. As can be seen, its a good remedy, but takes a bit of time to dry out.