Balsa dust
I have a standard operating room mask (the old formed piece with the formable metal nose clip) for dust. I forget to wear it al the time and sneeze and cough of balsa dust to no end. But it is a good point; wear a dust mask when sanding. It makes the job much easier.
When the filler is a little dry, I put a few drops of water into the jar and stir it in thoroughly with a stick. This really helps getting the filler to apply evenly onto the balsa. Moistening the surface works well too, but barely moist, not wetting. I prefer to moisten the filler in the jar. It spreads nicer.
When filling tiny nicks, the filler dries in only a minute or two. When larding it on, I wait about an hour, and then first flatten it with 80 grit. It is normally still a hair moist but it actually smooths out better before it is totally dry. I read somewhere on a technique of sanding it moist and it really works nicely. It takes a little practice to know when it is ready, but it really feathers out well and smooths in amazingly.
I plan on trying my friends dope and talc method. One of CPLR's experimental wings is in the shop today and the dope and talc looks pretty nice. The drawback on the dope and talc method is that it takes longer to dry, and it is important to wait about 2-3 days after the last dope/talc application for covering as the shrinkage is a little more evident than the NHP.
Mark