I have the same little piles of grey stuff, one in the corner of the bedroom and one in the corner of the bedroom closet, on top of the baseboards, about one inch high and one inche wide each of them....old 1940s house but no apparent pests, and no sign of any grow mould....only thing unusual in this town is that the water has high amounts of sodium in it....but these piles are nowhere near any water....water lines are all at other end of house...i am thinking some kind of spider nest or something...???Jack at bizmastr33@yahoo.ca
