I have marks on my deck that look like brown or black watercolor has been spread on sections of the board. What is this and how do I remove it?
These marks are most likely tannin. Tannin naturally occurs in all wood products, reacting with water and other materials to form stains. The marks look somewhat like brown or black watercolor has been spread on sections of the board. They may also be described to as watermarks. In some instances they may form as small pinpoints of dark black or a light gray on portions of the board. These marks are on the surface of the material and do not affect the structure of the deck. These marks may sometimes appear after a deck is installed and is first exposed to wet weather. Material that is stored without proper covering can also develop tannin stains. Many of the stains described above will lighten over the normal 12-16 week weathering period. This process can be hastened with the use of a product containing Oxalic Acid, normally called Deck Brighteners.
