Black Spots Terrace

Black spots on the terrace

Terraces are a place of relaxation and recreation in spring and summer. Unfortunately, black discoloration can form on some planks over time, detracting from the overall appearance. What are the causes of this discoloration and how to remove it?

Causes of black spots on the terrace

The black spots on the terrace can be caused by the so-called tannin oxidation reaction (also iron-tannin reaction). This is a natural reaction that occurs when wood comes into contact with base metals such as iron. The tannins in the wood oxidize and cause unsightly discolouration. Depending on the type of wood and the material used, the discoloration can vary from deep black to bluish black and even greenish spots.

Iron oxidation decking board
Stains Garapa decking
Stains Garapa decking

Removal of the black spots on the terrace

Luckily, there's a simple solution to getting rid of black spots on decking: oxalic acid. Oxalic acid is an organic acid that is found in many green plants, such as spinach or rhubarb, and dissolves discolouration on wooden surfaces. The oxalic acid is biodegradable. It is naturally broken down by various bacteria and fungi and is therefore an environmentally friendly alternative to other chemical cleaning agents. That is why Bettwood offers it onlineshop as a patio cleaner. In addition to stains, slippery biofilm can also be easily removed after winter with the patio cleaner. We have explained here how best to proceed with cleaning:

Protect sensitive surfaces

When cleaning, two things should be considered in particular. Firstly, using pressure washers is an absolute no-go! The water jet, which is often too strong, not only loosens the wood fibers but also opens and enlarges the surface of the wood and thus creates a breeding ground for moss and algae. The green tinge becomes more and more difficult to remove over time and the wood suffers long-term damage.

Also, one should be careful when using oxalic acid. Even though it is a dilute and weak acid, it is still an acid that requires protective clothing. In addition, caution is required when sensitive surfaces are nearby, as oxalic acid can lead to oxidation stains that can no longer be removed. Visible glass and metal surfaces in particular should be masked off against splashes before using oxalic acid.

Terrace cleaner as a solution for black stains on the terrace

Black stains on the terrace are a common problem, but they can be easily fixed with the help of oxalic acid. The tannin oxidation reaction is a natural reaction that cannot be influenced. With the right cleaning, however, you can ensure that the terrace shines in new splendor again and that you can enjoy your time on your own terrace to the fullest.


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