Let’s talk tannin

What is tannin?

Tannins are natural compounds found in various plants, including oak trees, tea leaves, and certain fruits, that can cause staining when they interact with other materials, especially when moisture is present.

In the context of wood, tannin staining typically refers to the discoloration that can occur when tannins within the wood react with moisture or metal components like nails, screws, or fasteners. European Oak contains large amounts of tannin which naturally bleeds and washes out of the timber as it dries. 

As the oak is exposed to moisture, the tannin can be released and migrate to the wood's surface, reacting with any metal components in contact. This reaction leads to the appearance of stains.

How does tannin affect my building?

When the Oak is fresh cut or green and used externally, large amounts of tannin will wash out of the timber. This will also happen when dried Oak is used externally. 
Tannin is a natural dye from the Oak and may stain surrounding building materials such as bricks, concrete, paving blocks etc. This stain will appear as a brown water stain and will spread as far as the water running out of the Oak reaches. 

These unsightly dark stains can be a concern in construction and woodworking projects, where the appearance of the wood is valued, however it is important to note that the structural properties of the oak are rarely affected.

How to treat tannin?

Tannin is a natural dye and, over a period of time, will naturally wash out of the areas or products it has stained, the process will stop, and the staining will completely disappear. 

If the staining needs to be removed before it naturally washes away, it can be treated by mixing oxalic acid or bicarbonate of soda with warm water and spraying on to the affected area. Leave it to soak and then wash it off with a hose or pressure washer. 

Although the staining can initially seem very damaging and long-lasting, this method of treatment has been used very successfully in many applications.