Just to get the facts right, isocyanates are not filtered out with a charcoal canister mask. Isos are bad things and you should avoid them at all cost. I use a fresh air breathing system when I paint. It is the only way to know you are safe. Everyone reacts differently from isocyanate exposure. For some it can be deadly, for everyone it is bad. It stays in your system, so it is additive. It effects you more the next time etc. If you don't believe me, look it up yourself. You see people on TV spraying in professional booths with only a canister mask. First, there are lots of stupid people in the world. Don't copy others bad mistakes. Secondly, they are painting in a better environment where the airborn paint particles are taken out through there filter system quite well. That is not the case with you guys painting in your garage or make shift booth. You are exposing yourself. For this reason, I avoid isos whenever I can. I do all my priming with epoxy. Not all epoxies are the same. Mine , you can sand and block as you do with 2K primers ( isocyanates ). Or I use polyester primers for high build, no isos. I don't like to wear the breathing system all the time and in this way I can avoid it. But when its time to spray clear or other catalyzed top or under coats, I wear it. Learn and live healthy guys.