Hi all,

I'm refinishing what appear to be white oak floors in a house from the '30s. After finishing sanding the first bedroom, I vacuumed one last time then cleaned the floor with water + vinegar -- maybe that was a dumb choice, because the next morning I had black iron spots all over the floor.

Yeah, I lost it for a good 30 minutes.

Thankfully, after reading a bunch of articles and testing different scenarios, oxalic acid cleaned up 90% of the spots in ~5 minutes flat.

But it left me with 2 questions:

1. How do you properly rinse the oxalic acid off the floors? Everything I've read said to "rinse 3 times" with "plenty of water" (diluted with baking soda), and allow the floor to "dry fully" before proceeding. I can't imagine pouring water on so that it pools, but mopping with a damp mop doesn't seem like enough either.

2. What should I plan to do for the rest of the house?

Should I plan to use oxalic acid on each room, regardless of spotting, so that any bleaching is matched and spotting prevented? Or should should I avoid oxalic acid unless absolutely necessary?

Was this caused by the vinegar mix, and should I clean the other with just water? or maybe mineral spirits?

Are oil-based finishes safer to use than water-based with this kind of spotting? Is one better behaved after oxalic acid than the other?

Thanks!

You need not clean the floor after you finish sanding to bare wood. Just sweep or vacuum the floor. Oxalic acid will dissolve better in hot water. Rinse with hot water and then vacuum up with an indoor/outdoor vacuum, or absorb the water with plenty of towels. You may not get it all off, but rinsing without letting the water soak in will remove as much as possible. Work in small sections, then force ventilate with a box fan in the window to dry the floor. A hair dryer will dry spots that get too wet.
Applying a water-based finish will be a disaster. Use a solvent based finish like oil-based poly-urethane.

Thanks for this tip. I did a light sanding after the oxalic acid to remove some bleed / discoloration, then vacuumed and used oil-based sealant + poly. It all worked out!