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.

Salt damage looks like wood blossoming in a bouquet of tiny splinters or fuzz bursting from a wooden surface. The damage is mostly aesthetic unless you work with the wood on a daily basis, like on a ship. If you have to touch it often, it becomes a nuisance. If the salt-damaged wood has joists or attached hardware such as fasteners, those can become points of functional concern over time.  

To begin, the initial kernels of this research commenced decades ago with a very uncooperative, very determined fungus.

A tenacious wood fungus was discovered and studied by FPL researchers during a 1971 field stake preservative test. This fungus was very different than other wood-rotting fungi because of its extreme wood preservative tolerance. FPL researchers gave this mustard-yellow fungus the acronym, TFFH, a.k.a. The Fungus from Hell. TFFH was officially first documented in 1952 by a forest pathologist who called it Poria radiculosa and noted its ability to quickly decay even creosote-treated wood.

Fast-forward to 2011 when a distributor for a company specializing in fungus removal incorrectly identified salt-damaged docks, piers, homes, and surfaces in southern coastal states for TFFH. He conjectured that FPL researchers released TFFH into the environment. He created such a public fuss that Kirker, who specializes in salt damage, was called-in to diagnose the suspected areas. He was able to debunk such claims and correctly identify the areas for salt damage.

It’s understandable that salt damage is often mistaken for fungal decay.

Salt-damaged wood can appear to be sprouting tiny hairy invaders with a white powdery layer underneath. Though what is actually happening to the outer surface layers of the wood is flaking caused by exposure to salt, whether from briny water, deicing salt, or even salty soils. The white powder is known as efflorescence, excess salt residue deposits.

Wood damage examples (a) salt damage (b) brown rot decay (c) white rot decay (d) soft rot decay

In 2015, the National Park Service (NPS) contacted Zelinka when the San Francisco Maritime Museum feared their historic ship, Eureka, was suffering from a fungal invasion. A white, fuzzy corrosion was forming in the ship’s bilge. Traditionally, bilge salt-packing was used to prevent rot. But the salt-packing did a lot more to the Eureka than was expected. Decades of this traditional treatment caused one of the bilge joists to collapse.

Knowing Kirker’s extensive salt-damage identification experience from the 2011 incident, Zelinka asked Kirker to join him on the project. “The Eureka was an amazing opportunity because it gave us the chance to see and study a worst case scenario for salt damage—that boat was salty!—and also work with some great folks at the NPS Maritime Museum in the process,” explained Kirker.    

During their work on the Eureka, Zelinka and Kirker decided that more needed to be known about wood salt-damage processes and their team-up began.

They contacted George Scherer, an engineering professor at Princeton University specializing in concrete salt damage, to collaborate on the project. About to enter retirement, he declined but sent them a gift instead.

“Scherer and his group at Princeton had developed a chamber to simulate severe salt damage to concrete in a laboratory setting. In one of our meetings with Scherer he mentioned he had an extra chamber and asked if we were interested. We now have that chamber at FPL and are using it to conduct mechanistic studies to simulate salt damage in a laboratory setting,” Kirker explained.

Photograph of the experimental methods to control salt exposure. (a) The apparatus including the enclosure to maintain the relative humidity; (b) a close-up view of the wood samples in the salt solution.

Then they hit a dead-end. Once they completed the wood sample salt testing, they needed someone to interpret the structural changes the salt may have caused. Christian Brischke, a wood biology and wood products researcher at the University of Goettingen, “had developed this resistance to impact milling (RIM) test to measure structural integrity of small specimens. We had looked at how to do the test in the United States but couldn’t find the equipment. So, we eventually asked Brischke if he would work with us and mailed him the samples,” Zelinka said, crediting his co-collaborator.

The results Kirker and Zelinka got back were reassuring for using wood in briny environments and salty exposures.

“Salt does not damage wood except in very severe circumstances. It is mostly a surface blemish and doesn’t cause wood to fail unless there are some other underlying circumstances. Wood is a great material for marine use and has a proven track record. Even in a broader sense, roundwood poles and pilings are critical to our nation’s infrastructure, so we want to make sure they provide maximum service life,” reported Kirker.

Though treating salt-damaged wood is complicated, usually accomplished by sanding down the outer layer of the wood surface, the public can be assured that salty fuzzy wood is still doing its job. However, Kirker and Zelinka are quick to note that this treatment can only be used once or twice. Too much sanding will eventually cause structural damage.

Since the late 1990’s, it has been unclear whether salt damage structurally impaired wood and, if so, by how much. Because of Kirker, Zelinka, and their research collaborators, we now know that only minor structural damage, a maximum of about 6 percent, results from prolonged salt exposure.

But there’s still more work to be done.

Despite this substantial advancement in wood salt-damage research, it’s still unclear whether salt damage is mechanical or chemical. “If we can better understand what causes salt damage, it will lead us closer to developing a treatment or at least some better answers for users of wood who have experienced this problem,” explained Kirker.   

So, this salty tale has more to reveal in the years to come.

Finally, would Zelinka and Kirker recommend old-sea-dog sailors to continue packing their bilges with salt? “Definitely not! There are better, more effective ways to keep your boats afloat,” they explained with a smile.

To find out more about the amazing advancements our scientists are making, visit the Forest Products Laboratory at: https://www.fpl.fs.fed.us/