There are two schools of thought on sanding the bottom.
We've read a bunch of material on the "do" approach. The paint itself says this.
"PREVIOUSLY PAINTED SURFACES: In Good Condition: Remove loose paint by sanding with 80 grade (grit) paper, wipe with Special Thinner 216."
We've talked to some folks who suggest that we are doing too much preparation by painstakingly sanding the entire hull. Emphasis on the pain.
The "remove loose paint" clause is confusing. I may be sanding too aggressively. Way beyond remove loose paint.
We've also found this kind of information online. [Emphasis theirs.]
"MICRON EXTRA – Uses Bilolux technology to reduce slime. Good for all boats in all waters. Can be relaunched without coating and can be applied over existing paints. Remove loose paint by sanding with 80 grit (dry) and wipe down with 216 thinner. If you have a good strong application of any Micron technology paints on your hull, no sanding is required for a recoat. Simply powerwash the paint, scrub with a brush, let dry and reapply at least two coats with brush, roller, airless or conventional spray and extra in high wear areas. Colors: Blue, Green, Red, Black, Shark White (gray), Brown and Dark Blue."
No sanding is required for a recoat. Simply scrub with a brush. I'm guessing this is a stiff steel-bristle brush that will remove loose paint. I've heard that a Scotch-Brite pad does well, also.
For example, there's this on the Interlux forum.
The Micron Extra w/ Biolux and the Micron CSC are in fact compatible and the power washing/scrubbing with the Scotch Brite Pad would be plenty suffice.
If changing paints only requires scrubbing with a pad, then using the same paint may only require some scrubbing with a pad. Apparently, Interlux disagrees internally on exactly how to sand: the can says 80 grit, the experts say a Scotch-Brite pad.
Some sanding appears necessary. What's at issue here is precisely how much sanding.
I bought some "N95" dust filters. The first one turned pink from the bottom paint dust. An old Tyvek suit we had laying around has seen it's last paint job.
Perhaps I've done too much. I'm hoping that extra prep is not too harmful. Just wasteful of time. And potentially destroying our shopvac with fine particulate everywhere.
Next step is wash down with the 216 solvent. And then roll on the paint. Hopefully we'll be done soon.