Dan, in your excellent post you mention "dry micro". Do you mix it until it seems about right, or is there some more scientific way to get a consistent result? I am concerned about getting different percentages of epoxy in successive batches. This would tend to make some areas harder to sand. Bill Newkirk
Very good Bill. There should be no successive batches.
Different density with different batches will indeed result in uneven sanding.
Always apply a reasonable excess with the first application. It may seem to add sanding time, but in truth it's faster than repeated applications to correct low spots, and way less time to get looking good.
In general, mix fill micro as "dry" as possible. It should be spreadable, but not run off the mixing stick. The ratio is something like 5 to 1, micro to mixed epoxy,
by volume. More dry is easier to sand, more epoxy is harder. You can develop a recipe if you want, but why bother for a one-time small project?
Wear a dust mask when you mix micro. Microspheres are light enough to float in the air and you'll breath them.
Microspheres are great insulators. If you mix a batch of micro and leave it in the container more than a few minutes it will exotherm, i.e. the cure heat of the epoxy can't escape and you'll get a thermal runaway in the cup. Lay a sheet of 4-mil plastic on the bench, mix the micro, then dump it all out on the plastic and spread it thin. Cure heat will now be able to escape, so it won't exotherm, and you'll have time to work it. Tomorrow, any waste micro will pop right off the plastic.
Obviously, use slow hardener.