I tried to remove black marks from wood floors with Bar Keeper’s Friend recently, and I’m happy to report it worked pretty well.
Here’s the story: I had some mysterious black ring-shaped marks on my hardwood floors. I traced them to metal ends of furniture legs. The long-term solution is to put the furniture on leg cups, but one still has to contend with the damage.
The pros use a floor bleach whose active ingredient is oxalic acid, but finding it is hard, and finding it in household quantities is harder. But there’s a cheap, readily available household alternative: Bar Keeper’s Friend. It costs a couple of dollars and you can buy it at big-box stores like Home Depot, hardware stores, grocery stores, and even some discount stores. It’s usually in the cleaning aisle next to the Comet. It’s good stuff to have on hand anyway, because it does a great job of cleaning up pretty much anything you’d use Comet on, but it literally eats rust spots for lunch so it’ll take care of chores Comet doesn’t.
Mix up a bit of Bar Keeper’s Friend with some water into a thick paste. Apply it to the spot and let it sit a few minutes. Scrape the paste away enough to look at the spot. If the mark disappeared, wipe up the paste. If not, put the paste back (apply more if need be), wait a little longer and try again.
The Bar Keeper’s Friend will probably lighten the area where the mark had been. You can touch up the spots with a stain marker or a bit of wood stain applied with a cotton swab. Matching existing wood stain is extremely difficult to do, so be ready to try more than one shade of stain. I’ve even seen flooring professionals mess up these matches. The good news is, if it’s a small area, it will be hard to notice.
Apply stain with a cotton swab because it will slow you down. Apply a bit of stain with the swab into the affected area, and immediately wipe it away. If it’s too light, apply a bit more. Ideally you want to wait about 30 minutes between applications so you can judge the color better. Don’t expect perfection, but those spots will look a lot better when they’re gone. Put a bit of painter’s tape near the area to mark it. Let the stain dry for a few hours. Once you get the color as close as you can, put a bit of water-based polyurethane on the spot to give it some extra protection.
Whatever you do, be sure to get those protective cups onto the legs of the furniture that’s causing the marks. Since it’s a bit of work to clean it up and it probably won’t look perfect when you’re done, you don’t want to be doing it again.
And that’s how you remove black marks from wood floors if you’re not a flooring professional. Expect it to take 30-90 minutes, depending on how many marks you have. But it’s not an especially difficult or expensive project. It’s a lot cheaper and less time consuming than refinishing the whole floor.