Refinished floors this weekend using the Varathane EZV orbital sander - the extent of cupping of the floor boards made it a painfully slow process (8 hours just to take off the finish and level for ~275 ft^2), but that's another story. Used Minwax oil-based stain and let it dry ~12 hours before we made the first poly run.

What a disaster. The can says something on the order of 750-1000 ft^2 per gallon - we couldn't spread it thin enough to get anywhere near that, a single coat for the 275 ft^2 used almost a whole gallon. The can made no mention of thinning, but it obviously needs it - it doesn't flow at all. We used 4" Purdy brushes to apply, but every single brush mark showed when we checked it 8 hours later. I sanded a couple areas (where we started and where we stopped) with 400 grit paper, got white powder, and figured it to be dry so we recoated (can stated 8 hours to recoat).

Recoat was done with a lamb's wool applicator in an attempt to smooth over and cover brush marks.

Results - awful. Some veining/bubbling occurred, maybe the first coat wasn't entirely dry. Other areas look rough and on inspection look to have very fine lines through them - not quite applicator lines, they're very fine twisty lines, almost like a fine fingerprint or brain pattern. Some areas are perfect. Is this a matter of dry time? Perhaps I got lucky and tested areas that were dry and weren't fully representative of the whole floor.

So...remedies. We were hoping to have this done before we moved in, but Friday is move-in so it looks like we'll be fixing this while we live there. Will a hand-sanding with 220 do the job, or does this sound like it requires a full screen with a heavy buffer? Anyone have experience with this poly and it being incredibly thick (the water-based we used elsewhere in the house was like skim milk, this stuff is like warm honey)? After getting the imperfections out, is acceptable to go to a water-based poly?

You probably got some of Minwax's low VOC crap in the gallon cans. They take all the solvents and dryers out and you're left with that "thick honey". Impossible to do a good job. I suggest you let the floor dry thoroughly (2 weeks) and then, if you're up to it, hand sand it twice; once with 150 to remove the flaws and then again with 220 to smooth it out. A buffer is easier but unless you're familiar with operating one, I'd recommend against it. You could use that square buff thing with finer sandpaper as well. Then buy the Minwax Quick Dry oil based poly in QUARTS. A different finish altogether. Much easier to use and quite durable. Not as good as Bona Traffic but doesn't cost $100.00 a gallon either. Also, those 12 hr. dry times are for FURNITURE, not floors. Floors require about 48 hrs dry time using MINWAX stain. Other brands dry faster.

Thanks for the help Gary! About 85% of the floors are perfect, there are just localized areas of alligator skin and bubbling. Would it be possible to locally sand out the bad spots and reapply the same poly to those areas, or is the poly never going to match due to environmental conditions, blending the new with the old areas, etc.?

For clarification on the hand sanding, you literally mean hand sanding, not a palm sander or anything powered, correct? The square buff "thing" you mention, is that another powered buffer that you suggest we could use for finishing? Would 320 grit be sufficient, too much, or too little for use with that?

Since everyone loves pictures, we sanded off this pickled finish and restained with a pecan (dining room and foyer remain to be sanded):

This is after the second poly coat - it's still drying so it retains the high sheen.

If you follow Gary's directions you will be fine. If the alligatored areas aren't too big or numerous, hand (like the thing at the end of your arm) sand those areas and the entire board(s) they fall within with 150 - 180. You don't have to sand out the irregularities completely, but you need to sand out most of the roughness, so it is level with or, below the finish around it. Then spot coat these areas. It might help to mask the repairs on the board edges. Recoat the entire boards. Pull the tape off a few minutes after the finish was applied. Let this cure for a couple of weeks if you are going over it with water.

Hand sand (using a sanding block) any big bumps 180-220. Then go over the entire floor with 220 to abrade it, and to remove any remaining small bumps. The flat rental sander will probably be fine for this. Check your paper often, and change it when it fills up. If you see clumps on it, you are moving too slow, and melting the finish.
Good luck
Pete

Thanks Pete. On further inspection, we decided to sand the whole floor. We've hand sanded everything with 150, removing drips and other areas that we hadn't noticed before. Today is 220 day, and we'll be using the quick dry Minwax poly Gary recommended. We had some debate about using an applicator pad versus a roller, but I think we're going to stick with what we know and use the applicator. We'll also probably be very generous with the dry times, since we certainly don't want to hand sand a 300 sq.ft. room ever again.