The Dirty Rotten Truth about Dry Rot
by Sonnie Layne
Over thirty years ago, when I was new to the thought that thinking could be beneficial, I was introduced to this nasty destroyer. James Vittaliano pointed it out to me and explained what it was while we were restoring an old building in the French Quarter of New Orleans. He explained it to me something like this… "dis be what hoppen when dis wood git wet, den him get too dry for old time, cher". Well, Mr. Jim had it partly right. In the years that insued I educated myself amongst other interests, in botany.
One of the interests of botany is mycology, the study of fungi. I learned of the structure and nutritional needs of a number of fungi, but mostly the higher orders, i.e. "mushrooms" and "tree shelves" and the like. Still, when I found myself back in the construction industry it was like ~ déjà vu all over again ~ when I linked in my feeble mind the apparency of a fungal "infection" with the decay of wooden structures. Indeed I have joyed at times unearthing a log buried for a few years on my property to find and smell the rich remains of a noble giant reduced to what we avid gardeners call compost, complete with the actively growing fungus.
Well, my curiosity went wild on me (as it often does), and I remembered the interior walls and crawl spaces of those properties in le vieux carre. Ahhh, the years and the books and the interest have been rewarding for I have learned something of this phytopathic behaviour. Well maybe not phytopathic, that would explain the behaviour of the human animal's intimacy with herbicides I guess. I'm not a learned or educated man, so please someone tell me what it is when one organism…….ohh, yeah, parasitic. Kinda like a lot of people I've met. Funny how we tend to exlude ourselves like that. At any rate, Mr Jim was partly right…
The plant I will discuss has been taxonomically named Serpula lacrymans, at least that is the descriptor of what I have learned to be the primary cause of habitat deconstruction in the U.S.. It really doesn't seem to matter what form the wood is in. It will attack living trees both softwood and hardwood. It's even been noted to attack standing conifers. To me this is notable because of the existence of terpenes and other isoprenoids. I haven't yet seen a piece of "rich" or "fat" pine attacked even when apparently surrounded by the organism. As the cellulose is destroyed a discolouration frequently occurs, leaving what remains of the wood appearing pink or purple hued. There's probably some relation between this and the fact that carotinoids, which are also isoprenoids, are plant hormones involved in the appearance of these colours in plant tissue (love those autumn colours). I haven't gotten into it in that depth. If I did I don't remember. There are at least two other organisms which have been identified as the precursors of dry rot, Poria incrassata Merulis lacrymans. I haven't read as much about these two species.
The term dry rot itself is rather misleading and a misnomer. Mr. Jim's thought explained to me that it was a breakdown of tissue in the absence of moisture after being saturated with water. So very close was his thinking. As with most all fungi, Serpula lacrymans requires moisture for it's spore (microscopic "seeds") to germinate, and a certain amount of free moisture seems to be necessary for it's initial development, but once mature the source of water can be a great distance away from the mature fungus and the wood affected. Other requirements for the fungus are appropriate temperatures, somewhere between 45 and 90 degrees Fahrenheit and of course wood, the food source. I've read that the fungus, once mature can survive in woods with moisture content of 20%. It's unknown to me as to whether or not it's true, but I think the norm for kiln drying lumber is to reach 19% moisture content, and I have no doubt that the powers that be have considered all these things.
The structure of trees on a cellular level, without getting into detail, is akin to stacking cardboard boxes made of sugar, on top of and next to each other and gluing them together with Elmer's (what be called lignin). When a fungus destroys the cellulose, the sugars are umm what's the word…respired, yes, leaving these empty boxes and that's why when you see wood affected by a fungus, it appears like little cuboidal shapes, darkened by some reaction involving CO2, I don't remember. It crumbles away between your fingers into a million little die (what be one dice).
The fungus begins it's life with the germination of the spore, kinda like microscopic seeds. The spore needs free moisture, wet wood like from a leaky roof, bad gutter, drippy plumbing etc. Then the hyphae are formed, which are kinda like roots, but invasive and excretive. They excrete enzymes which begin breaking the wood down. As this happens, the wood becomes even more porous, absorbing more moisture which is grand for the fungus, right? Well guess what? It doesn't stop there, the by-products of this whole chemical process is CO2 and….duhh….H2O! Now folks, you can call it a dry rot, but it ain't. If you don't give it water, it'll make it's own with the right conditions. And if the conditions aren't right, the mycelium, or actively growing portion of the fungus can hold specialized thick-walled hyphae called strands that go looking for water. It's been documented that these strands can find moisture 20 feet away, even across masonry surfaces.
Somewhere there's some thought that these strands can even effect the strength of the masonry surfaces they cross by interacting with the masonry chemically. Seems maybe the fungus uses oxalic acid to break down the cellulose in the wood and requires calcium found in masonry to neutralize this acid when it's no longer needed. This could in turn make the masonry more porous and capable of absorbing moisture. Worse yet, if it's in the right spot (and it usually is) simple condensation could take place interstitially and provide moisture right there in the cement! Nasty stuff. This is like "Survivors" done right!!!
So, what to do about it all? Well, most remodeling contractors I come in contact with just ignore it (read ignorance) thinking "Hey, it ain't wet, we fixed the leak, so no problem". Then they ~might~ nail some new wood to the old wood to provide structure so they can nail a new window/door in, or tile over it, or put vinyl siding over it. Then the cancer spreads and you won't even know it because it's covered with a material that won't be affected. I call it the "Big Bad Wolf Syndrome", blow your house down. Scaring you yet? Well, OK, I'll stop but there's more if you're interested.
About the best we can do is what I call "Going through the motions". You can remove the crumbly stuff, but as you've learned you're not affecting anything. The fungus is out in front of what damage you see. You may be able to see the mycelium (white cottony looking stuff like your kid put cotton candy on the carpet) ahead or behind the area. Then again you might not. Nothing says the mycelium has to crawl around on the surface. The only times I've seen it do this in the presence of extremely right conditions as I outlined earlier. Under your house is great. Under your roof is even cool. Here's a picture of dry rot affecting a roof decking.
Note the white mycellial growth. Even further up the
roof you'll notice a bit of discolouration (pinkish colour) that would indicate
the presence of fungal activity. Left unattended, this condition could spread
not only across the roof, but into adjacent soffit, fascia and rafters (now
we're talking structural damage).
Here's my procedure for dealing with it, and it's no guarantee but the best sensible approach I've come up with short of fumigating with formaldehyde. Remove as much material as I can. In the photo, for instance I would replace the whole piece of plywood. Again in this case, I would likely spray a metallic fungicide like copper sulfate or arsenate onto adjacent surfaces. In other cases, such a window sills or trim work I may leave the crumbly stuff to build on. With an awl, I find the next closest solid wood. I understand it may only appear solid, but I typically don't carry an electron microscope to job sites. If possible I extend out from that point two or three feet and begin injecting a chemical suspending a plastic. Call it acetone and plastic. Now you can buy it over the counter as Min-wax wood hardener. What I expect to happen is this… the cells absorb the carrier with the plastic. The acetone kills any fungus present (desiccation?) and evaporates, leaving the plastic resin behind bonded to the wood "fiber". Now you have plastic wood we can build up like automotive body work. I use Bondo, no need to pull punches at this point. It's the stuff you're auto body shop uses to fill dents and bangs in your car door. They make a composite for wood, but I can't really tell the difference. It sands, drills, nails and paints wonderfully. The repair will be around long after the wood (and myself) is forgotten.
Given all that I've learned about the fungi, it's good enough. I don't like it, and it ain't perfect, but it's good enough. Certainly beats ignoring it or nailing up new wood only to become infected again. And it sure beats "a poke in the eye with a sharp stick" as my dear friend John Weiss would say.
I'm researching the use of borates (boric acid) to combat the fungi, but effective application is a problem in enclosed areas. By the time I figure it out, the US will probably outlaw it's use. Just FYI… the mycelium can survive 12 months or so on masonry surfaces. Under humid conditions, the mycelium can remain active for 10 years on wood. The spore are viable for 3 years.
Have a good night's sleep.
©Sonnie Layne 2001
This article was "lifted" from Sonnie's web site: http://www.sonnielayne.com
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