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Dec 08, 2021

How to Remove Black Marks on Lumber

Tags: How To

If you frequently work with wood, you may have come across pieces that have black spots or streaks on them. These streaks tend to look like ink or oil stains and are often relatively easy to hide or cover. However, you may get a spot that you just can’t seem to conceal. Unlike other discolorations that occur while the tree is still growing, these black streaks can be removed. So what exactly are these marks, and how can you get rid of them?

What Are Those Ugly Black Marks?

These back marks are called metallic discoloration, or iron stains, caused by elemental iron reacting with phenolic chemicals in the wood, forming black iron tannates. Iron stains require the presence of iron, water, and wood and will not occur if one of these elements is absent. So, if we know how these marks occur, why can we not prevent all metallic discoloration from occurring?

How Can Metallic Discoloration Be Prevented?

Sawmills do their best to prevent these marks. However, sometimes they just can’t be avoided. Wood is moved all around these facilities using forklifts that have iron forks on them. Any moisture that accumulates on the forks from rain or snow can then cause metallic discoloration where the forks come into contact with wood. At Marks Lumber, we pay special attention to ensuring our forks stay dry, wiping them off periodically throughout the day.

Mills also contain metal chains that are used to transport materials throughout the facility. Any rain or snow that accumulates on the logs before entering the mill can have enough moisture needed to cause discoloration. At Marks, we will often shut down the mill on rainy or snowy days to help minimize these stains.

Even with these precautions, some discoloration can still occur. In Stud mills and S4S mills, that’s where the planing process will take over. Any reactions that have occurred are simply planed off when these facilities surface their material. At Marks Lumber, we specialize in circle sawn lumber, meaning it will not get planed. Instead, we do our best to separate the materials with too many black marks and downgrade them during our grading process.

How Can I Remove Iron Stains?

For lighter marks on products such as flooring and siding, a simple sanding will often remove the stains. Additionally, dark stains or Lifetime Wood Treatment can also help cover or reduce the appearance of the marks.

For the more severe marks that can occur on boards and timbers, Oxalic acid can be applied. Oxalic acid works by creating a chemical reaction with the iron stain and forming a colorless chemical complex. Perma Chink’s Oxcon is an excellent Oxalic acid solution that can help you get rid of those unsightly iron stains.

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