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How to Remove Black Stains from Hardwood Floors

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Hardwood floors are a popular flooring option in homes. They provide a warm and beautiful appearance, and can last a very long time. However, they are prone to dark stains and other damage. Knowing how to remove black water stains from your hardwood floors can be a useful skill to help keep your floors looking sharp.  

Unfortunately, when your hardwood floors have black water stains your options are limited since the stain has penetrated through the floor's finish and caused wood damage. However, that doesn't mean you have to accept the ugly black stain. There are some things you can do to lighten the stain and sometimes remove it entirely. But keep in mind, your results will largely depend on the extent of the damage.

Removing black water stains from wood floor

How to Remove Dark Water Stains from Wood Floors

When it comes to removing dark water stains from hardwood floors there are a few methods you can try before jumping into the sand-and-refinish option.

Before getting started it's a good idea to remember that no two black water stains are the same, so if at all possible you should experiment on a small area before tackling the entire stain. Otherwise, you could end up with a bigger problem than you started with.

Bleaching the Stain

There are a number of products you can try in order to bleach the stain. In fact, you might already have some of them in your cupboard. 

Although your results will largely depend on the original cause of the stain and the age of the stain itself, you'll likely be able to at least lighten the stain and possibly even remove it entirely.

If the black water stain was caused by urine, there's likely an odor as well. This is because there's a large build-up of dried uric salt crystals present. Using vinegar or hydrogen peroxide will not only help remove the stain, but also eliminate the odor.

Hydrogen Peroxide 

One of the advantages of using hydrogen peroxide is it'll also eliminate the odor from your hardwood floor. This makes it a popular choice for black pet stains.

In most cases, you'll need to apply the hydrogen peroxide a number of times, so it'll likely take you several days before you have your final results. But the process is easy and doesn't take a lot of time.  

Simply place a towel over the stain and saturate it with hydrogen peroxide. Let it soak for at least 8-hours. Reapply until the stain is gone.

Watch a Video

White Vinegar

White vinegar is another method that will not only remove the stain, but also eliminate odors. 

Mix one cup of warm water with one cup of white vinegar and scrub the stain with a rag. Use a paper towel to pat the area dry. Before reapplying, we recommend allowing the area to air dry overnight. Often it will continue to lighten.  

If you're not satisfied in the morning, simply repeat the process.

Baking Soda

Another option is to create a paste by mixing vinegar with baking soda.

Apply the paste to the black stain and allow it to dry before wiping it off with a clean towel or rag. Reapply as needed.

Sanding and Refinishing

If you didn't get the results you were hoping for by bleaching the stain, then you can sand and refinish the stained area. In many cases, you'll be able to remove the stain completely and bring your floor back to it's original beautiful look.

There is more work involved with this method, but if you enjoy DIY projects, it's not too difficult. Before starting you'll want to be sure you have a matching stain available as well as a top-coat so you can re-seal the floor.

Many homeowners aren't comfortable doing the sand and refinish method themselves. So if you fall into this camp, you may want to hire a professional to tackle the project for you. 

Here's what to do:

Step One: Use a fine grit sandpaper over the stained area moving with the wood grain.

Step Two: Once you've removed the stain with the sandpaper, clean the area with a vacuum.

Step Three: Find a stain that matches your floor and apply it using a clean cloth. Then let it soak for 30-minutes before removing the excess stain with rag.

Step Four: Allow the stained area to fully air dry, then apply a top-coat that matches your floor. Typically the top-coat is wood varnish or lacquer, but older floors may use wax. The important thing is it needs to be the same as the rest of your floor, otherwise it will stand out.

Depending upon the damage, you may not be able to completely eliminate the black stain, even with sanding.

However, in most cases you should be able to lighten it enough so it blends and no longer stands out. After sanding, you can try a wood bleach such as this one made be Zinsser.

Wood floor with black spots

What Causes Black Water Stains?

It's not uncommon to have water marks on a hardwood floor under a potted plant or near a window. These are called moisture stains, and although undesirable, they are less noticeable and not nearly as ugly as black water stains.

Since water itself is clear, it will often leave a moisture stain on a hardwood floor. But it's important to know that if your hardwood floors are exposed to moisture, they can develop black water stains.

The black color of the stain generally indicates that the moisture has penetrated through the floor's finish.

But not all black water stains look the same, and how the stain presents itself is often an indicator of the reason why that area of your floor turned black.

Here are some common stain patterns and their causes.

Chemical Stains

If you have irregular-shaped discolorations or black marks on your finished hardwood floor it could be the result of a chemical reaction with the floor's finish. There may even be a reaction to the wood itself.

Some common chemical stains are caused by ammonia, chlorine, iodine, oil, milk, nail polish, mustard, acetone, and ethyl alcohol, among other items.

Mold and Mildew

High humidity, pet messes, or any other reason your floors are exposed to moisture may result in mold and mildew.

If you have organic material and moisture present, you have the potential for mold growth. It's not uncommon for black mold to grow under your hardwood floors and remain unnoticed until a black or dark colored stain is visible.

Mold can become a serious health issue if left unaddressed. It's a good idea to contact a flooring professional to help you get it cleaned up. 

Tannin Pull

Many black water stains found on hardwood floors are caused by a tannin bleed. Trees and plants have a naturally occurring compound called tannin which offers a variety of protections from disease and insects, as well as helping to regulate growth.

As a general rule, darker colored woods, such as cherry, mahogany, oak, and walnut have a higher concentration of tannins than lighter colored woods.

Since tannin is water soluble, it may leave a dark stain when it comes in contact with water. Even water-based finishes can draw the tannins to the surface, which is where the descriptive tannin pull name originates. 

In fact, alkaline products, such as ammonia, can also be an issue with tannin and leave dark stains on your hardwood floors.

If you've ever tried to eat a piece of fruit that isn't ripe, you've experienced one of the many roles tannin plays in protecting trees and plants.

In order to discourage animals from eating the fruit before the seeds are mature, the unripened fruit has a high tannin content. As the fruit ripens, there's less tannin. The high tannin content prevents animals from eating the fruit before the seeds have matured.

Iron Stains

Have you ever seen a round black stain on a wood floor after lifting a metal bucket? These types of stains are often the result of a chemical reaction which takes place between iron, water, and the tannins within the wood.

You may also see iron stains if the floor was not properly cleaned of metal filings before a water-based finish was applied. When this happens you'll typically see small black dots scattered across the floor or clustered in a specific area.

It's also possible to see black circles surrounding flooring fasteners or nails if they were used to secure your floor in place.

Anywhere there's water and iron present there's an opportunity for a black iron stain to develop.

What Causes Blue or Brown Stains?

Here are some of the common causes of blue or brown stains on hardwood floors: 

Sticker Stains

During the seasoning process, the wood is stacked with thin strips or boards (called stickers) between each board. The stickers allow the air to circulate while the wood is drying.

Unfortunately, the stickers will sometimes leave a brown or blue stain on the board. When this happens you won't be able to sand the stain out. Because of this, many flooring grades allow for sticker stains.

Sap Stains

Sap stains occur within the sapwood of a tree, which is the wood near the outside of the trunk. The cells in the sapwood are still alive and metabolically active.

Sap stains are more common in standing or fallen timber, and can even occur while the wood is seasoning prior to being kiln-dried. These stains are a result of fungi.

Once the wood has been kiln-dried, its no longer living and the fungi will not spread.

Since it isn't a mold, there's no health concerns. In addition, the structural integrity and the wood's strength remain intact.

All grades of wood allow for this color variation.

Black vs White Water Stains

Another common hardwood floor discoloration is the white water stain. Unlike black water stains, where the moisture has penetrated through the floor's finish and damaged the wood, a white stain is not as serious.

Water or heat can cause a hardwood floor to develop a white stain, and since it only affects the floor's finish, these stains are typically easier to repair.

White stains are often found on floors with a lacquered finish, and seldom seen on older oiled wood floors.

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