I've just been out sanding the edges of some mouldings and I took the usual dust mask precaution (Moldex 2405 CE121) and I've just blown black bogies!  It wasn't really bad but this sort of thing bothers me.  What mask should I be using?

I use my SF10 gas mask from my forces era for anything toxicish. Anything really bad i have a full self contained breathing apparatus set up.