Wood Floor Turning Black – Causes + How to Remove the Stains

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Wood Floor Turning Black – Causes + How to Remove the Stains

Black stains on your hardwood flooring should be cause for concern. Dark marks and spots will dampen your home’s interior aesthetics. And if you’re looking to put your property up for sale, black stains on the wood floor will lower your home’s value. That’s why you need to know why your wood floor has black stains and how to remove them.

Water moisture damage and pet urine can make your wood floor turn black. Moisture and dampness provide an optimal condition for black mold to thrive. Use bleach, vinegar, and hydrogen peroxide to remove these stains. Sanding and refinishing hardwood can be the last resort for extreme dark stains.

Why is my wood floor turning black?

If you have black stains on your hardwood flooring, it’s most likely as a result of moisture, mold growth, or pet urine. We’ve discussed each of these causes in detail below:

Why is my wood floor turning black?

Water Damage

Water damage on wood floors can be a result of various factors. You may have over-irrigated your indoor plants, causing excess water to pool on the floor surface. Or maybe, there is a leak within the plumbing passing through your subfloor, causing moisture to penetrate to the surface of the wood floor.

Moisture damage may cause black staining on your hardwood flooring, as tannins within the wood grain chemically bond with the water. The water-damaged spots will look like mildly charred wood.

Unlike white water staining that indicates that the moisture damage hasn’t extended past the surface finish; black staining should let you know that the moisture has seeped into the deeper layers of the hardwood grain. As such, it takes a lot more work to get rid of dark wood floor stains caused by water.  

Mold Growth

One of the main reasons for wood floors turning black is mold infestation. Black mold growth on wooden surfaces is usually encouraged by the presence of moisture. Water that pools up on the surface of your hardwood flooring, and is not immediately dried up, will encourage the growth of mold fungi. Mold growth on wooden surfaces usually appears as black/dark staining.

Whenever you notice black mold spots atop your hardwood floor surface, it usually means that the mold infestation is at an advanced stage. That’s because mold growth typically begins at the intersection of the subfloor and the bottom of the wood planks. This section of the floor provides the type of dark and humid habitat that molds prefer. Afterward, the mold spreads to the top of the hardwood flooring.

Pet Urine

If you don’t immediately clean up your pet’s urine, it will soak into your hardwood flooring, causing dark stains. Urine contains ammonia, which triggers wood discoloration.

Urine also creates a moisture problem, which encourages the growth of black mold on the wood surface. The black stain won’t be your only concern when it comes to pet urine, as it also leaves behind a strong, unpleasant odor.

How to remove black stains on hardwood floors

To effectively remove black water stains from hardwood floors, you need to take action depending on its causes. Here is how to remove stains as a result of moisture, mold, and pet stains.

How to remove black stains on hardwood floors

Removing Black Moisture Stains on Hardwood Floors

Blackwater staining is usually a sign of prolonged water damage to the wood material. Thus, it takes a lot more than baking soda or mineral oil/spirits to get rid of this type of stain. The steps below will show you how to effectively get rid of black hardwood floor stains caused by moisture damage:

  • Lighten the Stain using Bleach

For such deep water stains (black stains), sanding alone won’t cut it. First, you need to lighten the stain by applying bleach to it. The bleach will cause the wood grain to rise to the surface. Chlorine bleach is strong enough to eliminate mold growth spurred by the water issue.

Mix one part chlorine bleach with eight parts water. Then, add a cupful of baking soda to the solution. Transfer the solution into a spray bottle and apply it to the blackened sections of the hardwood floor. Let the solution sit for about five minutes. Once done, wipe off excess bleach using a dry piece of cloth or a paper towel.

  • Sand and Stain the Hardwood Floor

With the stained sections now lighter after bleaching, you can sand down the planks before refinishing them. Use only fine-grit sandpaper (100-120 grit) to avoid getting rid of the lightened top section of the wood. Finish off by staining the planks to the original color of the hardwood floor.

Removing Black Mold Stains on Hardwood Floors

You can tell that the dark stains on your wood flooring are due to mold growth and not pet urine through the differences in odor. While pet urine has a strong, ammonia smell, mold spores carry an earthy, musty smell. Mold can trigger various health issues and should be controlled as soon as it’s discovered. To get rid of black mold stains on your hardwood floor, follow the procedure detailed below:

  • Remove the Hardwood Planks

Whenever you notice black mold stains on your wood floor surface, it’s highly likely that the problem started out from (or has spread to) the subfloor. You should, therefore, start by uninstalling the hardwood planks to access the subfloor.

Start by removing the baseboard trim and transitional trims. Then, take out the hardwood planks one by one. This takes some elbow grease, especially of the planks that were nailed down to the subfloor. However, it’s important if you want to completely get rid of the mold problem.

  • Clean the Subfloor using Vinegar Solution

Once you access the subfloor, the mold-infested sections will be easily noticeable. Before using vinegar, wear a pair of hand gloves, as prolonged exposure to this natural acid can trigger skin irritation. Mix a cupful of distilled white vinegar with a gallon of water inside a mop bucket. Then, stir the mixture.

With the vinegar mix ready, dip a mop into it, lightly wring the mop, and run over the affected areas of the subfloor. It’s important to mildly wring the mop as you don’t want to create the same moisture problem that led to mold growth in the first place.

Once done, let the vinegar absorb the mold spores for about ten minutes before rinsing the floor with clean water. Finish off by drying out the entire subfloor using a dry mop. Once the subfloor is fully dry, reinstall the hardwood floor planks and trimming. Make sure to replace the planks that have mold stains with new ones. Alternatively, you can sound down the affected planks and reapply the original finish. You can also mix baking soda and vinegar to kill mold by taking advantage of both cleaning agents.

Removing Black Pet Urine Stains on Hardwood Floors

If the dark marks on your hardwood surface as a result of pet’s (cat/dog) urine. Follow the procedure below to get rid of the staining:

  1. Apply a few drops of hydrogen peroxide solution over the stained floor section.
  2. Next, wet a piece of cloth with the same chemical solution (hydrogen peroxide) and lay it flat over the stain.
  3. Now, create a poultice by laying cling film over the soaked clothing that you’d placed over the stain earlier.
  4. Let the poultice stay in place for up to half a day to soak in all the pet urine from the hardwood.
  5. After 12 hours, remove the poultice and clean the area. We recommend using a solution of one part white vinegar and one part water. Acidic vinegar works to neutralize the ammonia in the urine, thereby getting rid of any lingering odors as well. Then, let the wood flooring dry out.
  6. Once the floor is dry, check if there are still any traces of pet urine stains left. If so, lightly sand the area before finishing it with a stain that matches the original finish of the floor.

Can Engineered wood floors get black spots (stains)?

Engineered wood floors feature multi-ply core construction and a surface layer (design layer) made of real wood. As such, this disadvantages the engineered wood planks flooring since it can also soak in water and get black spots, just like natural hardwood floorboards.

However, this is rare, as the core layer material of most types of engineered wood products boasts water-resistant core construction. The core material may range from laminated timber to Oriented Strand Board (OSB). Most cores feature adhesion additives for enhanced water resistance.

Read More; Laminate flooring vs engineered hardwood: what are the differences and its pros and cons.


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Joe McGuinty
I’ve been working with floors for over 12 years. I started as a flooring contractor, primarily in materials selection. Then, I switched careers into accounting, so my wife and I began buying, renovating, and re-selling homes on the side. You’d be surprised how much value you can add to a home simply by adding new floors.

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