This is pretty specific to my experience on tour in Java yesterday. I went up to the rim of a caldera of a volcano which had erupted last year. The roads were ok, but on some dips and flats there were deposits of what I thought was ordinary sand which were washed in by the constant rain. Last night at the lodge parking lot I was giving the bike the once over and realized that it was volcanic ash residue, lots of shiny little bits (silicate). The staff helped me wash what we could out of the chain and brake discs. These guys then told me that since the eruption they have been going thru brake discs like crazy (changing once every two months!!). As soon as I get a chance I am going to get the bike to professional wash to get whats left blasted out with water jets or whatever they're called. Any tips/thoughts?