Types of Log Rot, Rot Fungi & Wood Decay on Log Cabins

Dawn SmithLog Homeowner Education

Log rot funguses… the ever-consuming organism hungry for the flesh of wood. Under a microscope, it looks like a beast from a horror movie: no eyes or mouth, tendrils stretching and always spreading. Wow! That was a bit dramatic. For some, log rot can be like fighting a beast regarding maintenance on your log home. Log rot is best known in its three forms of fungi:

These three forms result in different residual products of decomposition. Please allow me to explain them as best I can.

The Brown-Rot Fungi

Brown-rot fungus is a destructive fungal disease of trees and shrubs. It mainly damages fruit trees, causing a possible 50% loss before harvest. It also affects log cabins everywhere.

Cubical Brown rot on oak looks like it is crumbling. Picture taken from https://en.wikipedia.org/wiki/Wood-decay_fungus on 11/19/2020.

Effects of Brown Rot Fungi

You can see the effects on almost any nature walk as it devours the remains of a once mighty tree that lies crumbling back into the earth. Brown rot’s byproduct or decay is the crumbling part of the tree, often called dry rot, because of its appearance and an 18th-century misunderstanding of rot.

Different Forms of Brown Rot

Brown-rot fungi come in different forms: dry rot, mine fungus, and cellar fungus. Softwoods like pine, spruce, and cedar are among the most susceptible to this fungus and the most common wood used to build cabins. It is typically found at high elevations, such as The Rocky Mountains.

Soft-Rot fungi growing on logs. Picture taken from https://en.wikipedia.org/wiki/Wood-decay_fungus on 11/19/2020

The Soft-Rot Fungi

Soft-rot fungi are fascinating as they have been studied in extreme conditions where brown and white rot cannot thrive. It can also devour high levels of compounds typically resistant to biological attack. Scientists are still studying and discovering new things about this abnormal rot.

Soft Rot Fungi Mysteries

“Decay caused by many common white and brown-rot fungi has been well characterized, but other types of decay, such as soft rot by fungi or bacterial degradation of wood, are not well understood1 ,”

says ASM Journals under Wood-Destroying Soft Rot Fungi in the Historic Expedition Huts of Antarctica where they studied 100-year-old huts from early expeditions.

Soft Rot on Vegetables

Picture of Soft Rot from https://aem.asm.org/content/70/3/1328 on 11/19/2020

We often see a white cotton-like soft rot, also called white mold, on our vegetation or greens in the fridge. Scientists are still actively studying this unique and fascinating mycelium. It often makes the wood look like it is eroding. You can easily confuse it with brown rot, which is more common.

“Soft rot cavities in pine wood that was in contact with the ground from the exterior of Cape Evans hut. The secondary walls of tracheid contain numerous cavities of varying size.”

See picture of soft rot under microscope to the above right. Also where quote was taken.

Microscopic Soft Rot Cell Walls

“Soft rot resulted in decay usually characterized by chains of cavities that form within the cell walls of wood.2” The article is fascinating if you are a mycology geek like me. I will say this. It is, however, less effective at decomposing wood than brown and white rot. Because of the brown hue byproduct, soft rot can often be confused with brown rot. Soft rot on your logs often looks eroded.

The White-Rot Fungi

White-rot fungi can appear stringy and spongy. Picture taken from https://en.wikipedia.org/wiki/Wood-decay_fungus on 11/19/2020

White-rot fungi are recognized for their breakdown, bleached appearance, and stringy or spongy mass. It may also appear in select areas known as pocket rot. White rot and brown rot differ from what the fungi breakdown. I will save you the geeky details.

Yummy Fungi

Unlike brown rot, white rot typically feasts on hardwoods such as oak and birch. White rot, under the right conditions, can damage an entire wood structure. Did you know Oyster mushrooms are the most cultivated white-rot fungi? Turkey tail, The Artist’s conk, Tinder fungus, and Shiitake mushrooms are white-rot fungi people can recognize (see below).

Now that I have familiarized myself with the types of rot, you might be wondering what you can do to keep them from inviting themselves into your log structure. Identifying problem areas is a crucial step. One thing you should do is identify problem areas.

Look for these Problem Areas

Problem areas, such as window seals and logs touching the ground, retain moisture. Look for moisture contributors such as sprinkler system placement, minimal overhangs, and damaged gutters. Be mindful of the northern sides of your home for objects (like shrubbery too close to the house) blocking the sunlight, which dries the logs after getting wet. To learn more about planning the layout of your log home on the property and how it will impact your log home services, read “Log Home Landscaping Wisdom.”

Log Structure Landscape Planning Ideas
Log Structure Landscape Planning Ideas to help you plan for your log cabin appearance, maintenance, and restoration. This image may be complex to read from your mobile device. Please consider viewing it from your computer for more details in the image. You can also email [email protected] to ask for the original picture to help plan.

And remember to look for already affected areas. The rot must be removed early to avoid more extensive damage and costly restoration. If the rot is above any logs, you can guarantee that the ones below will also begin to rot as water travels downward by gravity. Finally, you need to have regular maintenance from a professional.

Maintenance from a Professional

Professionals who are experienced in log home maintenance and restoration can perform regular maintenance to prevent offenders from causing havoc.

Hire a Certified Log Home Inspectors

If you are buying a log home, we highly recommend you hire a certified LOG HOME inspector from the InterNACHI. Home inspectors are not often trained to inspect a log home. For a more details on protective measures for your log home investment, call a Log Master.

Log Grade and Wood Ratings

Check out the EN 350:2016 Standards by the APA-The Engineered Wood Association for more information regarding wood ratings for durability to fungi and insects. To learn more about log grade, watch or read about it in A Hardwood Log Grading Handbook.

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