Have you ever looked at wood siding on a house and noticed black spots and runs around nails? What are these marks and where do they come from? This same kind of black mark can occur on Marks Lumber products. We have had customers call to say that there are grease and oil stains on their rough sawn wood. These black marks are called Metallic Discoloration or Iron Stain and are caused by elemental iron reacting with phenolic chemicals in the wood to form black iron tannates (common black ink pigment). Iron Stain requires the presence of iron, wood and water and will not occur if one of these elements is absent. So, how do the black marks get on Marks Lumber’s material?

• Of course, as we are a Sawmill, we have lots of wood, so that covers the first element.
• We have forklifts with iron forks and metal chains that are constantly moving and transporting boards and timbers around and through the sawmill as the wood is being cut, stacked and dried. This gives us the second element.
• The third element is water - where does it come from and how does it get the material wet? The water comes from rain or from snow on the logs that melts as we process them in the mill.

What does Marks Lumber do to prevent Iron Stain?

It is very difficult to prevent all Iron Stain on wood without having a huge indoor facility. Stud and S4S mills simply plane the black marks away when they are surfacing their material. We are a facility that specializes in rough sawn material, so we don’t have that option. We go to great lengths to prevent black marks but we can’t be 100% free of them.

• We are constantly wiping the forks on our forklifts to remove all the moisture
• We debark all the logs before we send them into the mill
• When it is raining, we either shut the mill down or only cut material that is okay to have black marks
• When we are grading material, we separate the material that has an over-abundance of marks and downgrade them to lower grades.

Can the Iron Stain be removed or covered?

The answer is yes, but it depends on the severity of the marks and what the material is used for.

• For light black marks on flooring and siding, just a simple sanding will remove the marks
• Stains and Lifetime wood treatment will cover the marks
• For more severe marks on boards and beams, Oxalic acid can be applied which reacts with iron stain and forms a colorless chemical complex. There are many products out there and we recommend the “Oxcon” product manufactured by Perma Chink. See the attached link. https://www.permachink.com/wood-cleaners/oxcon for instructions on use. Also see the attached before and after pictures of Iron Stain removed with Oxcon.

Sources, https://www.fs.usda.gov/treesearch/pubs/48449 https://fpinnovations.ca/media/publications/Documents/wood-discoloration.pdf