April 3, 2023

The Common Types of Hardwood Flooring Discoloration

Perspective of Hardwood floor in close up - Flooring Discoloration

Hardwood floors are some of the unique and valuable additions to your home. Many remodelers and interior designers call them pieces of timeless elegance for several reasons. The most notable factor why is that no hardwood flooring is similar to the other. Unlike other flooring options, hardwood planks have distinct grains and patterns that differ with each wood strip. Despite that, these hardwoods often experience discoloration and stains. Here are some common types homeowners can encounter with their wooden floors.

The Difference Between Stains and Discoloration

Contrary to what most homeowners think, hardwood flooring stains and discoloration are not similar. In the wood flooring industry, these flooring terms mean different issues your hardwood floors can encounter.

The USDA Wood Handbook describes wood stains as discoloration caused by diverse agencies, like microorganisms, metals, or chemicals. Meanwhile, discoloration is often a term that applies to the materials used in passing color to the plank.

Mineral Streaks/Deposits

Mineral streaks on hardwood floors are discolored lines, spots, or bands that range in color from light gray to tan. These deposits occur naturally, and many woodworkers and remodelers consider them as additional value and visual appeal to the hardwood.

Many streak stains are mineral deposits from the surrounding soil, like limestone, sulfur, phosphorus, silica, and gypsum. They can also be any other mineral local to the region where the hardwood species originated from.

Mineral streaks are due to the natural interactions between the living hardwood tree and its environment. Different flooring grades allow them because you can’t sand them out, and neither plank is identical to other boards, even if they come from the same lumber.

Sap Stains

Sap stains are wood discoloration coming from the sapwood. They’re often the result of particular fungi growth on the surface when the moisture content in the interior of the wood and other surrounding conditions are perfect for their production. When this happens, the hardwood becomes prone to fungi, even as fallen timber, or during seasoning before kiln-drying the hardwood.

The discoloration from sap stains is also called blue-stain or brown-stain because of the color coming from the fungi. Fungi in kiln-dried lumber are not living. They don’t cause any decay, mold, or spread. Unlike fungi in living hardwood trees, these are not concerning to your health and will not affect the structural integrity or strength of your hardwood planks.

Sapwood is the active wood near the exterior of any living hardwood tree. They tend to have lighter colors than the heartwood. Homeowners should be careful not to confuse them with sap stains because sapwood color variations are normal and acceptable in all wood grades. 

Sticker Stains or Shadow

Sticker stains come from the thin strips or boards used to separate layers of lumber during seasoning. They function to permit air circulation in the pile when getting seasoned. Sometimes, these stickers leave a brown or blue stain that develops on areas having direct contact with the boards.

Sticker stain discoloration results from naturally occurring chemicals within the hardwood during the drying process. You can’t sand them out, but many flooring grades allow them.

Moisture Stains

Hardwood planks and flooring finishes sometime change color due to exposure and moisture. Many stains you encounter in your homes deal with moisture-related issues. They’re often moisture-induced rust, pet feces, urine, and mildew. Concentrated moisture levels in your floors can create these stains and are difficult to remove.

Iron Stains

Iron stains result from a chemical reaction between wood tannins, water, and iron. They’re most common when you leave scraper filings or abrasive materials from the floor before applying water-based finishes.

Iron stains become more apparent from flooring fasteners, metal buckets, and other objects placed on the hardwood floor exposed to moisture.


Tannic acid, including other naturally occurring, soluble, astringent, complex phenolic substances, are what trees use to protect themselves from insects, fire, and bacteria. Many hardwood trees, like oak, walnut, and mahogany, have high levels of tannic acid that can produce dark discolorations when in contact with some finishes or wood cleaners.

Tannic acid is water soluble and can discolor when exposed to iron and water, appearing as a bluish or gray-hued discoloration on the hardwood.

Chemical Stains

Chemical stains are irregular-shaped discolorations on some areas of your hardwood flooring reacting with certain chemicals and air pollution. These stains are often the result of a floor finish's reaction to household chemical spills or cleaning products, like nail polish removers, ammonia, chlorine, iodine, milk, and acetic acid.

Discoloration and Hardwood Floors in Austin, TX

Hardwood floors sometimes experience discoloration due to age, wear and tear, and exposure to pollutants and moisture. While some stains and discolorations on your hardwood planks are from chemical reactions during the hardwood lumber’s seasoning or cutting, there are instances where they become concerns to your hardwood flooring’s longevity. Understanding the common types of discoloration can help you identify which stains are problems you need to address.

Visit Kelly Hardwood Floors for more details about available hardwood floors in Austin, TX, today!