I acquired a wack of old timbers from a barn 3 years ago. I am hoping to start building with it. Unfortunately upon planing I am coming across a fair bit of dry rot. I can’t imagine chucking these large boards ( most are 2″ + thick 16″ wide and 12′ long). I am wondering if the dry rot can continue to spread if the moisture source is eliminated. If not I am considering filling the holes with coloured epoxy. Any thought?
Thanks N.E.T.
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There is no such thing as dry-rot. There is however such a thing as rotten dry wood, or wood that rotted while it was wet, which dried out later. As long as wood is kept dry, it will not advance, but once it is wet enough, the rot will continue to eat the good wood around it.
"Dry rot" is a colloquial term referring to fungal decay that occurs in wood that has already been dried and put into service (e.g., in a building). This is to distinguish it from decay that occurs in green wood.
Dry rot does require moisture to occur, of course.
-Steve
Steve, I am well aware of how and when rot occurs, I am not sure if you are disagreeing with me, unless, you are saying that the wood has to go into service after the rot has occurred. If that is the case, I have to wonder who builds with rotten wood?Most cases that I have run into this misnomer, is where there has been a leak for a long enough period of time that rot has gotten a good start, then someone fixed the leak, without replacing the rotten wood. Then later someone else comes along finding the dry rotten spot, and concludes that rot is occurring in dry wood. Duh, well I seen it wit my own eyes. HaMaybe I need to hear your definition for "green wood" and how decay occurs in it, and who would use it to build with after that.
You said that there was no such thing as dry rot. While it's true that wood that is dry will not decay, I was just pointing out that that's not what the term "dry rot" means. "Dry rot" refers to decay that occurs in wood that has been dried at some point. Obviously, it's not dry at the time the decay occurs. While I agree that some people may think it means decay that occurs in dry wood, that's not the historical usage. I believe the historical distinction between "dry rot" and "wet rot" (decay in green wood) arose because the species of fungus involved, and consequently the nature of the decay, are generally different in the two cases.
You're free to consider "dry rot" a misnomer, but it's a term that has been in use for hundreds of years (at least), so good luck. ;)
By "green wood" I mean wood that has never been dried, wood as it comes from the tree.
-Steve
The magic number is 20% EMC. And on the shores of Hood Canal with 70" of rain from October to June, the wettest the DF frames of my open sheds ever get is around 16% EMC. Molds and their successor decay fungi need above 20% moisture, above 55 degrees F, low UV and low air flow for their spores to germinate and become active. Eliminate those conditions, and spores don't germinate. That's why outdoor wood is usually kilned to 19% or 'KD-19". Just enough to kill the beetle larvae and stop blue stain from forming in the sapwood. What generally damages building frames/decks around here is a roof leak in warm weather or winter consensation that puddles on the wood, raising its EMC.
A baseline EMC for green DF is 30% EMC, although it can easily be wetter depending on soil moisture and growing conditions. In our summer droughts for example, DF lower trunks are usually below 30% while the upper limb areas are 40% and higher because available moisture migrates upwards to the needles for transpiration.
A major advantage of DF with its excellent strength-to-weight ratio is that it remains relatively dry in outdoor and marine service. DF heartwood is actually less rot-resistant than White Oak heartwood, but in a boat keel DF remains drier because it is less dense. Consequently the WO keel spends a lot more time above 20% EMC than the DF does, making the service life of the two species about equal.
One of our tree farms has a well-drained footbridge built around 1940 across an old beaver dam. The high-ring-count DF heartwood deck exposed to the weather for almost 70 years still provides safe footing, fungi or no fungi. Chopping out your punky wood and treating with CPES followed by filling with thickened epoxy will fix your wood permanently. In large spots you can bed some Dynel fabric into the epoxy if you think you need the stick's original full strength. Easier than fitting a Dutchman.
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Edited 9/13/2007 11:14 pm by BobSmalser
Thanks Bob,
Great information. You got me thinking, my property backs on to a creek and I've been meaning to build a dock of sorts. Perhaps I could use the punkiest of my wood for this application. Are the floor boards intentionally angled for drainage? Forgive my ignorance but what is CPES?
Thanks Dan
CPES is a pentrating epoxy sealer some by Smith Enterprises and available there and at Fisheries Supply in Seattle. A super-thin epoxy sealer designed to isolate punky wood followed by reinforcement with full-strength epoxy. It's very effective, seeps deep and thickened epoxy can be hotcoated atop it before it's dry.
That footbridge is askew because the frame is logs and rubble atop a silted-up beaver dam. Both the beaver dam and the rubble settled and the logs rotted. Some day I'll have to tear it out and build something else involving concrete footings and FOHC DF beams.
Edited 9/14/2007 10:28 am by BobSmalser
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