A Salty Tale of Wood Damage Research and Discovery

A tenacious fungus, a conspiracy theory, a historic ship, a unique gift from Princeton University, and two Forest Products Laboratory (FPL) researchers, Grant Kirker and Samuel Zelinka, collaborating with researchers from Germany and Canada all converged in the right order of events to produce some of the most significant advances in wood salt damage understanding in over twenty years.

Samuel Zelinka – Supervisory Materials Research Engineer
Grant Kirker – Research Forest Products Technologist

A recent publication, “Salt Damage in Wood: Controlled Laboratory Exposures and Mechanical Property Measurements,” is the result of all of these circumstances and characters clashing and aligning.

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Cottage Conundrum: FPL Fields Cleaning Question

All of the research and expertise of the Forest Products Laboratory (FPL) is in vain if we can not use it to better the American people. Our lab receives many questions for our researchers, and recently, we received a question regarding T1-11 cedar siding.

Dear FPL,

I have a problem with the T1-11 Cedar Siding (plywood) that was installed on my cottage back in 1986. There is a black fungus on all sides of the cottage, even where the front is exposed to the direct sunlight most of the day. I would like to have a vinyl siding installed over the T1-11, but am not sure if I should have that done without washing the siding first. I have washed the siding in the past and the fungus has returned! I would appreciate any advice you can provide to me.

Cottage Conundrum

Luckily, Mark Knaebe, a Natural Resources Specialist with the Forest Products Marketing Unit, had the answer!

Dear Cottage Conundrum,

The most important question here is what do you really have?  If you used what is commonly called a “wood bleach” which is oxalic acid, and it brightened up, then you have iron stain. Iron stain is not a fungus.  


Although it leaves wood black, iron stain is not a fungus. The above example was caused by corroded fasteners.

If you used a chlorine or oxygen bleach and it brightened it up, then you have mildew, which is a form of fungus, and it may not be a huge problem except it that it can keep wood wetter for longer periods which can promote decay fungus (rot) in very wet areas.

I would not give up on the T1-11 just yet.

If you are set on putting vinyl over it, and it is iron stain, you can ignore the black. If you have mildew, you should find out why first, and if bleach cleans it up, you could just bleach and put up the new siding paying special attention to proper flashing. Traditional penetrating coatings contained oils which are food for mildew so as soon as sunlight destroys the mildewcide, mildew can quickly return, so that might be what you’re experiencing.

The bottom line is find out what it is first, and take the next steps from there. Thanks for your question!



Fungi Friday : Shiitake Science Paved Path For Future Fungi

The following is adapted from Forest Products Laboratory 1910 – 2010 : Celebrating a Century of Accomplishments.

In the late 1970s, Forest Products Laboratory researcher, Gary Leatham, completed a doctoral thesis based on his research on growth of the Japanese Islands variety of Shiitake. Continuing his research at FPL, in 1982 he published “Cultivation of shiitake, the Japanese forest mushroom, on logs: a potential industry for the United States.”


Shiitake mushrooms, growing on sawdust rather than on logs. This research led to the creation of an alternative method of commercially growing these mushrooms.

This paper and a number of public seminars stirred a lot of interest and helped make commercial cultivation possible in the United States. It was also discovered that the edible Shiitake mushrooms (Lentinus edodes) grow faster on shredded oak residue than on logs.


Chittra Mishra, a research associate from the National Chemistry Laboratory in Poona, India, researching solidwood bioconversion using shiitake mushrooms.

This finding was a spin-off of long-term basic research toward selective degradation of lignin for biopulping. By producing Shiitake, low-quality hardwoods can be converted directly to a high-value food.

Shiitake growing has since become a budding industry in the United States, creating jobs and utilizing wood that would otherwise be wasted.