It’s possible that at some point in your wooden floor’s lifetime, you’ll encounter an area that has become darkened. This area might consist of a single, dark spot or there may be several spots or even several areas that have become discolored. The color might be a light greyish one, a deep, dark black color, or something in between. 

In this article, you’ll find answers to frequently asked questions related to the cause, removal, and prevention of black stains on wood floors. 

Is It “Normal” For A Wood Floor To Darken? 

This type of discoloration cannot be considered a “patina” of any sort as it is not part of any hardwood floor’s mellowing or aging process. Although it could be categorized as something that isn’t terribly unusual, this darkening is not normal. It is a stain and as such, it should be addressed. 

Why Are There Black Stains On My Wood Floor? 

If you weren’t on hand to actually witness the event or series of events that caused this, the cause is nevertheless evidence that an event has occurred. Dark stains indicate that a chemical reaction has taken place between the tannins in your wood floor and moisture or more specifically, the moisture’s level of acidity. 

If your hardwood floor shows no signs of warping, then the moisture is most likely to have come from above the floor rather than underneath it. 

Certain Types of Wood React More Profoundly Than Others

If your hardwood floors are:

  • Unsealed or
  • The seal has become worn
  • The wood has a high concentration of tannins
  • The grain of the wood is open

Then, depending on the acid content of the moisture it’s exposed to, it doesn’t take long for wood to become stained in this way. 

As with many hardwoods, their grain is one of the qualities that make them such natural choices among furniture makers. The grain’s detail and beauty are easily captured with a light application of stain or a mere rubbing of oil or bee’s wax. 

However, hardwoods contain higher levels of tannins. 

Proportional to the concentration of acids and minerals contained in the moisture, and the amount of tannins contained in the wood, the chemical reaction between them can be mild or quite profound. 

This Chemical Reaction Causes The Wood To Darken

Oak and walnut are particularly tannic hardwoods. Urine is a particularly acidic water based substance. The odor notwithstanding, the reaction between the tannic and uric acids is 

especially dramatic. 

All this makes it easy to imagine that a floor made entirely of hardwood could have several dark spots.  

If This Is The Case, Then There Really Is No Point In Crying Over Spilled Milk. Right?

Granted, by virtue of the fact that it can be so cathartic, crying certainly seems to have its therapeutic benefits. But because there continues to be a complete lack of evidence to suggest that crying can undo an event that has come to pass, the wisdom contained in the old adage also continues. 

As to its effect on a hardwood floor, it’s true that milk doesn’t contain uric acid. But milk does contain lactic acid. Lactic acid is ten times more acidic than acetic acid. If you think it will help you come to terms with it, then break out your crying towel because if it isn’t removed from your hardwood floor, even milk, whether spilled or intentionally applied, can cause the floor to darken. Harsh, I know, and not unlike urine, the smell is no picnic either. Sorry. 

Can Dark or Black Spots On Hardwood Floors Be Removed?

While the answer to this isn’t a 100% “Yes”, the outlook is certainly far from bleak. The odds for success are improved if you can answer “Yes” to the following:  

Have Offensive Odors Been Resolved? 

If there is a lingering odor, then whatever caused your floor to stain is still present. It’s possible for germs, bacteria and other unpleasantness as evidenced by the presence of odor, to be in residence underneath and in between the floorboards. 

Has The Moisture Been Resolved? 

Until the floor is completely dry, there isn’t much point in considering repair of the damage that not being completely dry caused. 

To Remove Dark Stains, You’ll Need To Remove The Cause

In other words, each of your hardwood floor’s boards needs to be thoroughly dry and odor needs to be treated. 

NOTE: This might entail removal of the undry boards. If you don’t have the skill or confidence to do this on your own, call your local flooring expert. If the expert is willing to remove the boards and then come back to install them once you’ve taken care of business, that’s even better. 

If your flooring expert suggests cleaning the boards with oxalic acid followed with borax, then do this. Follow his/her instructions to the letter. 

Otherwise, proceed with the following:

What You’ll Need To Remove Odor and Black Stains From Your Wood Floor

How To Get Those Smelly, Black Stains Out Of Your Wood Floor:

Remove The Floor’s Finish

  1. You’ll need to first strip the finish from the floorboards.
    1. to do this, be sure to follow the manufacturer’s instructions on the back of the container of the floor stripping product. 
    2. You can apply this with your paintbrush to be sure to keep the stripping solution contained to the affected area. 
    3. Use your plastic putty knife to scrape the lifted floor seal residue. 
    4. Use a clean rag to wipe and contain the residue from the putty knife. 
  2. Once your hardwood floor has been stripped, you might find the dark spots have lightened somewhat. This is to be expected. You’ll need to continue nevertheless. Especially if any odor is still present.

Remove Odor From Your Hardwood Floor

  1. Fill one of the spray bottles with the enzyme solution. Fill the other with hydrogen peroxide. Be sure to mark or label the spray bottles accordingly.
  2. Spray the affected area with enzyme solution. Be sure to spray in between the boards as well, but don’t drench the area or allow puddling. Allow the solution to dry. 
  3. Spray the area again with the enzyme solution. If after a few minutes, no odor is detected, pat the area dry. Otherwise allow the solution to dry.
  4. Repeat steps 5 and 6 as necessary.

Remove The Black Spots From Your Hardwood Floor

  1. Use your scrub brush to remove any residue from the affected area of your wood floor.
  2. Spray hydrogen peroxide well inside the area of the floor that has been stripped only. 
  3. Saturate a clean rag and lay it over the darkened area. Place another next to the first and continue until the entire darkened area is covered. 
  4. Cover the saturated rags with plastic wrap. Use a water jug or heavy book to keep the plastic in place.
  5. Allow the rags to remain in place up to eight (8) hours checking the rags occasionally to be sure they haven’t become too saturated with the stain to continue delivering the peroxide. 
    1. Replace any stain-soaked rags with rags freshly saturated with peroxide.
    2. Replace the plastic wrap 
  6. When eight hours have passed, remove the soaked rags from the floor.
  7. When the floor has dried, the stain should be gone.
  8. If some discoloration remains, use the sandpaper.
    1. Working outward from the center of the discolored area, apply light pressure and smooth strokes that move in the direction of the grain of the wood.
    2. If the natural color of the wood doesn’t begin to appear after three or four strokes, move on to the next area and the next, sanding these in the same way and using three or four strokes in each of these areas as well. Sanding will help to expose the pores in the wood, but too much sanding will result in dipping this section of floor.
  9. Repeat steps 8-14.

By now, the stains should be completely gone. If any floorboards remain darkened, sand these lightly. if the discoloration still isn’t gone, they should be replaced. 

How To Prevent Black Stains On Hardwood Floors

The key to preventing black stains on your hardwood floor is in understanding that its exposure to moisture doesn’t need to be terribly prolonged to cause this. 

  • Clean spills right away
  • Follow up with an appropriate disinfectant. Be sure to follow the manufacturer’s instructions. 
  • If you have pets, be sure to inspect your home routinely for “accidents”. Use an enzyme solution to clean these right away as well. We even have a detailed guide on cleaning pet urine stains & smell from hardwood floors.
  • Routine inspection should include a check for leaks you might not be aware of. Look under the sinks, the washing machine, and the dishwasher especially. 
  • If you discover a leak, place a container underneath it to catch the water, and dry the area completely. Continue to empty and replace the container until the leak can be repaired.

By taking care of problems before they start, you’ll save yourself a lot of hassle, stress, and energy…

…which of course, translates to more beach time.