Oakwood naturally contains a very high amount of a chemical called tannic acid. When tannic acid is exposed to metal and moisture, a chemical reaction occurs and results in black spots on your wood surfaces and floors.
Tannic Acid
Tannin occurs naturally in trees. Darker wood species such as mahogany and walnut and some oak subspecies have particularly high levels of it. The tannic acid that is within tannin can, if the wrong finishing product is used, react and cause dark stains and patches on your wooden floor.
When oak is cut using iron based tools (including steel tools), this can leave traces of metal on the wood itself. This will react with the tannins in the wood to produce bluish black marks. Handling in the workshop and during transport can leave dirty scuff marks on the wood and small dents.
Black spots are caused by water that has penetrated the finish completely and entered the wood. They cannot be removed without damage to the finish.
When you have black spots on a hardwood floor that clearly are not growing and spreading, if you can't simply wipe the floor clean, it's not mold. You have other issues, and they are likely not very serious.
If the structure of the wood looks damaged, in conjunction with discoloration, you may have mold. If the wood looks completely intact but is just slightly discolored, it might just be staining. If you can see the presence of spores on the surface of your wood packaging, then you're probably looking at mold.
Sugar soap or brick acid will clean it off if the customer is impatient. Oiling the oak will seal it and slow the loss of tannins to the point where it will wash away without staining the stone too much, but oil doesn't soak into wet oak very far as the water will stop it.
Black mold usually appears on wooden surfaces that have a water source nearby. Black mold can also grow on wooden surfaces if there is a nearby water source. Common areas include wood trims on bathroom walls, cabinets underneath kitchen or bathroom sinks, and wooden furniture found in damp basements.
Sap stains are a discoloration in the sapwood. These stains normally are caused by the growth of certain fungi on the surface and in the interior of the wood when the moisture content and surrounding conditions are prime for this fungal growth.
To restore the natural oak tones of the wood use 75-125g of oxalic acid per 5lt of hot water then apply by spray, brush or wipe on. NB: Oxalic acid is an ACID and therefore the correct protective equipment should be used- should your skin or eye come into attention SEEK MEDICAL ATTENTION URGENTLY.
Oxalic acid is particularly effective at removing the stains produced by metals, specifically nails. Often, the tannins contained in certain species of wood react with the iron in nails, producing dark stains which can only be removed with oxalic acid (oxygen and chlorine based bleaches are less effective).
Most pigment and tanin-based stains can be removed with minimal fuss if you deal with them quickly enough.
Brownish or tan discoloration on the paint surface due to migration of tannins from the substrate through the paint film. Typically occurs on “staining woods,” such as redwood and cedar, or over painted knots in certain other wood species. The stains are more noticeable on lighter paint colors.
If wood is painted with products not specifically designed to trap tannins, the tannins can bleed through to the surface resulting in brown, tan or yellow stains. Discoloration can also occur if wood is not fully dry when it's painted.
Pay attention to the color and consistency: We already talked about black mold above, though it's more accurate to say that Stachybotrys chartarum has a greenish-black hue. Toxic mold can also have a grayish, soot-like texture, or a slimy, wet surface. In some cases, you may even notice furry orange or brown spots.
If your wood is rotting and the black spots come with a dank, musty smell, you have black mold. It can appear distinct on different surfaces. On wet surfaces, it looks slimy and on dry surfaces, it looks like ash or soot.
In its early stages, it will be gray or green in color, and sometimes white around its edges. As it matures, it will darken, eventually achieving its eponymous black hue. Within damp and dank rooms, black mold is especially likely to appear on wooden surfaces.
However, the color black isn't unique to Stachybotrys — people often confuse it with similar-colored molds like Cladosporium, Aspergillus, Alternaria, and Dreeschslera. In earlier stages, black mold may appear more greenish-grey or greenish-black in color with fuzzy white edges.
Adding a little plain ol' household vinegar to your water bath can also help remove tannins! For really stubborn tannin stains, especially old tannin stains, you may need to use bleach to remove them completely, but try a few applications of water with vinegar and detergent first.
Definition. Tan or brownish discoloration on the paint surface. Tannins exist in many woods, most notably cedar and redwood and can bleed through to the surface, leaving a yellowish-brown stain on the surface. These stains are more noticeable on lighter paint colors.