We are doing more and more refinishes lately. Seems that's what's gonna carry us through the winter too.
I've encountered 3 different floors recently - 40 to 70 years old, with finish on them that I couldn't cut with 40 grit. We had to cut with 20, 40, 60, & 80 grit. Even had to edge with 20 grit on 2 of them.
I'm sure you guys know how much a roll of 20 grit norton paper is.

My problem is, I'm having trouble determining whether the finish will come off with normal procedure. Of course I'll charge more if I know we'll be doing such a rough cut, but these floors were in decent shape, with no obvious wax buildup, or any type of residue. I usually try to scrape a bit of finish off in a corner or closet to see if it's flaky, sticky, etc.

Y'all know a better method of determining how hard it'll be to sand off finish??

I feel your pain!!!! but unfortunately old floors need more love wich means more sandpaper. good luck and wish you the best on your flooring adventure. tom wentzwood

There's no scientific way to determine what you're sanding without a laboratory near by to test the stuff for you.Honestly, having sanded everything that is out there , I can tell by the appearance how nasty the floor will be to sand. IF I look at the floor and it has the color of danish oil or wax or murphy's oil soap, I charge more. And I let the homeowner be aware of what I see as well.

Rule of thumb, if the finish is clean looking and clear, it should be pretty normal.If the finish looks brown and hazy,it's got wax,oil soap or shellac on it and it's gonna be a pain.

That makes sense. Sure would be nice if I could do new floors consistently, just pass on these rough ones. Those days are gone though, around here at least.