We have probably all done it, used plaster next to track, or on scenery and it gets knocked revealing bright white spots. Easy to remedy with paint but I think I might have found something better.
I needed something brown to spread along side of track, covering sleepers, chocolate you might suggest
. I was considering ready mixed white plaster, bought some, but before I used it I came across some brown wood filler in local Wilkinson's store(it really is the replacement for old style Woolworth's) . Normally these wood filler are solvent based, but this looks more like plaster, so does not appear to attack plastics(yet). I spread some next to track, and left it overnight. I seems to dry very slowly, but there appears to be no adverse reaction, so I continued to use it on other parts of layout. As it is brown, it looks like dirt so if painted and then scratched does not show up badly. brown wood filler
Narrow gauge Francophile interested in 1m, 60cm,50cm , 40cm and smaller gauges . Build in scales from 1/6th to 1/24th. Also 1/32nd and 1/35th using 16.5mm track to represent 50cm and 60cm gauges. http://www.rue-d-etropal.com