Wot tazzy and jeff said. I wouldn’t be sanding old concrete with personal PPE. If I was asked to do this on a site, it would only be with a full face mask and a functioning dust extraction system. First and foremost I’d be trying to avoid doing it at all.
I think your best bet is to use a liquid dpm/primer on the concrete and then a thin skim of latex. Using the primer will give you good adhesion so you’re not having to depend on a deep build up of material for stability. Stick straight edges across the doors for a decent finish. Deal with trimming etc and just suck it up as part of the job.
As much as latexing and door-trimming sounds like a ballache, I think it’s the easier of the two options.
EDIT: Use a bottle mix latex, and leave a “handful” of powder in the bag. Better flow, like. 😀