Is charring really an effective treatment for ground preservation of wood?

I have heard this repeated many times in Permaculture circles and found the theory about why this is quite interesting but it bugged me that charcoal is like a sponge. Surely a charred log, placed in the ground will wick and hold water into the log and not stop rotting at all so I did some more digging.

http://juniper.oregonstate.edu/post-farm.pdf

This paper explores the results from post farm experiments. They found that charring actually reduced the life of an untreated post.

In another paper I read (I'll try and find it), they reasoned that charring has no effect because the charcoal does not actually form an unbroken coating around the wood. Fine cracks in the charcoal allow air and microbes to enter into the char/wood boundary and water is absorbed via capillary action, resulting in an ideal decomposition environment.


So what's the deal here? Is it a waste of time treating poles in this way?

Hi Nick,

I have seen this study, and several like it. I have a science background and because of that I have learned not to take research at face value. Even if the research is from a college, I want to understand the funding stream that supported the research. Are the researchers themselves affiliated with any large industry in anyway...often they are, and that creates a bias.

Lets just take this study that you reference as an example. 25 post are there sample study? To be blunt, that is ridiculous, you can't determine any kind of viable statistical factors with such a small sample. When I was studying turtles, if I had brought a sample of 25 specimens to my Field Zoology professor, he would have laughed at me and thought I was joking. Also note what species that was chosen for charring. Douglas Fir, well let see, what species could I pick that could be worse... Hmm, Aspen maybe, or maybe a Sugar maple. Why didn't they pick Cedar, or Locust for the charring sample? Again, I smell an agenda, conscious or unconscious, there is bias in this study.

Last, I would point out that, there was no reference to them being taught how, why or by what method they should char the wood. They took one of the worse species they could, burnt it, and stuck it in the ground. I'm sorry that isn't research, that is agenda setting bias, in my opinion and I know many in the science that are guilty of it. Were these folks, I don't know, but there research is weak at best.

There is a long linage behind charring wood as a preservative. Each culture had their own, and unless you have been taught a linage and method, and/or studied several I don't think anyone would be qualified to say it does not work, especially a retired professor, a grad student and all from the forestry department? I would listen to someone from the architecture or social anthropology department first, but that research does not seem to exist.

I have several of these lineages taught to me, should you have question, I will do the best I can. Start your research with the Japanese method: shou-sugi-ban. Then come back and ask questions.

Regards,

jay

Thanks for the reply. Every point you make I agree with.

I come from a computer science background and yes, 25 data points is basically meaningless.

Having spent a considerable amount of time and money in the area of preventative health, I am well familiar with the research tweaks and the various techniques employed in the name of science.

I'm also inclined to ask why? But why? Yes, but why?? I'm note being a prick about it, I'm just naturally curious and I know pretty much all data is biased.

If there is a rich cultural tradition around this practice then it certainly has merit. If more than one culture practices this then even better. I personally hadn't heard of this technique until I discovered permaculture so I am pretty ignorant on this topic.

Hi Nick,

Check out some of this and you may get more excited:

https://www.google.com/search?hl=en&safe=off&q=%E7%84%BC%E6%9D%89%E6%9D%BF&qscrl=1&ion=1&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&bvm=bv.43148975,d.dmQ&biw=1422&bih=792&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=WgM1UaeLGs6I0QHq_IGoAg

Regards,

jay

Hmmm, I see they also sand the char back to the (fire hardened) wood.
I wonder if its the wood/charr boundary that provides the protection. Everything's about edges right?

My Father's an architectural designer. He'll find this very interesting. Thanks for the link!

Depending on the lineage, charring is just a side effect. Carbon doesn't rot, but your observation about it being absorbent is good. Now just think, you take a piece of Cedar or Locust wood, hold it over a fire and slowly turn it, (one of many methods.) It not only will char slightly, (you don't want to burn it per say,) but it "case hardens the wood too. Now there even more steps, depending of style, but one that I have observed is you take a good wood oil, melt salt in it, then let the charred post bottom soak it all in, take it out let it dry, set it on fire quickly smother with sand or clay, repeat soaking. Like I said, many methods, and as far as I know this is the first time this method has been put to print. There is a lot of ancestral knowledge that Academics (myself included,) are just beginning to put to print, so much has been lost.

What is traditionally a good wood oil?
Castor oil?
Flax or sun flower?

Sorry, I don't know much about these things.

No worries Nick, we all start somewhere, I try to keep the "Buddha Mind" ..."the I don't know mind," on everything. That way, I'm always learning!

There are many, flax is the most common here in the states, you know it as "Boiled Linseed Oil," which is flax oil. Don't get the stuff that has just metallic or petroleum additives. The product I use the most is called "land ark" you can find it on the internet. If you have a project, present it here at the forum and I'm sure you will get additional guidance. Hill folk in Appalachia and Ozarks often us old motor oil. The other trick with fence posts, is back filling with gravel or stones not dirt. Even pine tree post can last 50 to 100 years with that kind of consideration.

Hope that helps...keep asking questions.

regards,

jay

I would not recommend Boiled Linseed Oil. In my experience, and through a simple google search, I found linseed oil is food for mildew/mold/fungi. If you live in a high humidity area like I do then I would avoid it like the plague. As I was putting Tung oil on a large project my friend laughed at me and told me to switch to BLO. What a huge mistake. I have to either shave down all the BLO off or start over.

Hello Dennis,

I am very sorry you had such a bad experience with flax oil. However, I would have to respectfully challenge your post as not being founded on complete facts, but maybe a bad experience or application. Flax oil has been used successfully for thousands of years. If you note, I gave a rudimentary formulaic suggestion, (not complete by any means,) that included salt, a natural fungicide and preservative. I also said I use a natural product call "land ark" which is a blend of pine rosin, tung oil, flax oil, bees wax, citrus oil, and if used for exposed settings, borate.

I do agree with you that tung oil very well may be superior in many ways, and for many applications. I do believe you need to reexamine you project and where, perhaps, you failed in the application of the flax oil, or the type or any number of stumbling blocks that come from using natural products. I too, have experience what you are describing with certain types of flax oil. My choice was to either start over or embrace the outcome. A wash of mercuric acid or bleach, (diluted and test as you go,) may well give you a new starting point. If this is an outside instillation, and you are not restricted to using a purely natural product like Land Ark, try a good nautical spar varnish. Remember wood is going to age and weather if exposed to UV or heavy humidity.

Best wishes and good luck with your project,

jay

Jay, you are full of amazing information! Right now I'm finishing a bath house with cedar siding and I'm now considering doing the exterior in shou-sugi-ban/burned cedar instead of finishing with a stain/preservative. Thanks for sharing that link.

Do you have any experience with burning other types of wood? I'm building a pole barn with doug fir board and batten (wind fall, rough milled, fairly green wood, if it matters) siding this summer and wondered if it would work with that wood as well?

The project with the BLO is a yurt I'm building from scratch. The BLO went on the lattice walls (khana) and we painted everything else. And you're right. I'm a beginner who had a bad experience with BLO from a box store. I was going to machine plain it off, but I'll try a bleach solution first. Would Oxalic Acid work? I have some for hide tanning and noticed it's main use is for cleaning tropical wood on boats. The spar varnish sounds like a great idea too (I was thinking polyurethane or paint).
Thanks, Dennis

(I'd post a photo of the yurt frame, but I don't want to hijack the thread any more than I have already...I will if folks want to see it)

Hey Dennis,

Thanks, I try to provide the best natural solutions to things I can, but often these methods though common and acient, aren't used much today. People have forgotten so much.

Do you have any experience with burning other types of wood?

Yes, but don't think of it as burning as much as case hardening and in some methods slight charring. Just about any wood can be treated this way, but you aren't necessarily done after charring, you still may need a coat of oil, depending on species.

I'm building a pole barn with doug fir board and batten (wind fall, rough milled, fairly green wood, if it matters) siding this summer and wondered if it would work with that wood as well?

I would say yes, but this species, unlike Cedar, may require an application of the "land ark." You can just spray it on with a bug sprayer or better yet, a rented commercial sprayer. The oil will go on finer and more conservatively. However, if you didn't oil it, the Douglas Fir would still probably last longer than it normally would without charring. With this species I would wire brush of the excess char.

Would Oxalic Acid work?

It may if diluted properly.

I just did an all wood Ger frame about two years ago, the Land Ark did a wonderful job on it, but still got some staining on the Ash wood from the sugar starches in the sap wood. I would point out that maybe you should just live with the black stains on the original BLO, hit it with some light sanding with 180 grit, then reapply something like Land Ark or the spar varnish. The wood will look aged and natural. Don't fret to much over the staining, it happens. If it where me, I would leave it alone, and learn to live with the natural beauty of the stains. Spalting in wood is beautiful, as is, blue stain in pine. Embrace the nature of things, don't fight against them, you will be more at peace with your craft if you bend to "it's will" than trying to make it bend you yours.

Good luck brother,

No matter what one does, in the long run, wood against soil is doomed to failure. Water always wins. If longevity is important to you, then use a system where the wood is not in contact with soil. I'm not a real "code" guy, but none of the structures I have seen where wood touches soil has lasted. Use a rubble trench foundation, sono tubes filled with gravel and capped, concrete(magnesium based if sustainability is important), whatever. Your foundation is the most important expense in time and money(along with your roof), that you will make. Been there, seen the elephant, as I'm a reforming engineering major. Yeah, I know, but who would have predicted when I started that being 50 would preclude a person from changing their career? lol
Don't worry about this. Just make sure your posts do not come in contact with the ground. No biggie. Good luck from us here in Alaska!

Hey, interesting thread, if you don't mind I'll direct your attention to https://permies.com/t/23082/green-building/Cordwood-experience-needed-burnt-charred where I'm soliciting opinions about applying this technique to a cordwood wall. Any input would be appreciated; I have zero experience with this stuff.


Cheers,

Hector

When you make biochar, you have to be sure to cook out as much of the resin and impurities as possible so the char will take up water and nutrients. Maybe it is the opposite you want on a post, a low temp burn with lots of resin.

Thought I would respond for some of the resent posts. David Stokes is correct, for this application you what to charr and case harden the wood that will be below grade. This "carbonizing" and raising resin in the process is how this "treatment" works.

Tom Jonas's observations are correct wood against soils are going to eventually biodegrade if not treated in some fashion. However, depending on region, and treatment this can be anywhere from 50 years to over a 1000s. Simple rules, no matter the species or region:

1. Backfill with only rock and have the bottom of the post resting on at least 200 mm of rock.

2. Treat the post bottom, charring is one and a combination of systems can be used.

3. Choose the most decay resistant species of wood you can.

Jay C. White Cloud wrote:]I would say yes, but this species, unlike Cedar, may require an application of the "land ark."

Jay, do you have experience charring cedar for exterior siding? I am hoping to do this on a house I am building and am having trouble finding information regarding how it will weather if it is oiled as opposed to not oiled, etc. I'm sure there are different techniques, how much char is left on etc, any info would be appreciated.

Andrew

Hi Andrew,

From what I have gathered, the charring of wood reached it's zenith in the Japanese method of "Yakisugi." I have only done limited work, more with unoiled, than oiled. Links and search parameters below.

Regards,

jay


japanese charred wood technique

http://pinterest.com/sbrothier/shou-sugi-ban-yakisugi/

http://pinterest.com/sbrothier/shou-sugi-ban-yakisugi/

Dang Jay, i am incredibly impressed by all your wisdom and beseech a little more details, please, from you and anyone with experience and insight We are just starting with a 5 high-tensile wire predator fence here in northern Sweden spanning a range of clay, muck, and peat soils and we definitely do not want to use commercial poison posts. The local tradition here is to hunt the most slowly growing Norway Spruces possible on the bogs or mountain tops, bark them out to dry, and then plant them as is, although there is some remnant knowledge of charring but no one can tell me the details of how exactly, how much heat how fast to what final effect. Most of my posts i am drying are around 4 inches on the fat end, although i will also use this for gate and corner posts that can easily exceed a foot in diameter due to the stresses on such posts over long stretches and is saturated muck soils, but i would estimate that typically they have 10 growth rings per inch and more if i can find it. So my first question is if it is better to char the posts when they are green, or dry? Second, how exactly do i gauge the charring process and know when it is optimal? Third, is there any benefit in charring the entire length of the post? Naturally they fail first at ground level and with the tops still rather "fresh" as this is a sunny and windy environment even if the soils themselves are often wet, so i know natural wood will hold long enough well above ground level but does it also possibly help wick water out of the post, whereas the char forms a barrier that should be restricted to the in and near ground portion? Thank you so very much to everyone for their enlightenment!!!

焼きすぎ- Yakisugi

焼き杉 - Shou-sugi-ban

There are different charring methods from different regions of the world, but the Japanese have probably taken the methods the furthest of all. It is done both for aesthetics and preservation.

So my first question is if it is better to char the posts when they are green, or dry?

I do not believe it is critical, but I like doing green as it facilitates the case hardening the wood and drying it out faster.

Second, how exactly do i gauge the charring process and know when it is optimal?

That is hard to speak to, as it comes with observation and experience, (you can do a Google Image search with the kanji above to see pictures.) I like to saturate the wood in turpentine and burn till charred to at least 3mm to 5mm in depth. I also, onced charred, like treating with Pine Tar Oil. This can be repeated over the life of the fence which, if maintained, could be a century or longer, depending on the quality of your work and maintenance routine.

Third, is there any benefit in charring the entire length of the post?

Yes, but this is dependant on you design. A charred "Z" split or log rail fence can last even longer as it is about grade. This goes for a stone scarfed or spliced fence as well where the below grade portion is stone and the wood post is scarfe or spliced to the stone.

Naturally they fail first at ground level and with the tops still rather "fresh" as this is a sunny and windy environment even if the soils themselves are often wet, so i know natural wood will hold long enough well above ground level but does it also possibly help wick water out of the post, whereas the char forms a barrier that should be restricted to the in and near ground portion?

I do not backfill with earth. Place a stone in the bottom of the post hole and pack stone tightly around post by hand. This provides proper drainage. Some elders would poor hardwood "Lye water" on and around the post once or twice a year as well, as well as "black lime wash." They may paint it on before placement as well.

Hope this helps.

That definitely helps, Jay, thank you! i am a measurements kinda guy, and so 3 to 5 mm of charring is well beyond the checking point, correct? i guess every tree species is different, and Norway Spruce does not seem to char as evenly across the surface as it feels that cedar must from what i have read...?

And to be honest i was always spooked by the gravel backfill even after hearing many i respected tell me about it because in North Dakota fence posts often seemed to rot off faster in the sandy soils than the clay. But these were not fence posts i had planted and so i was not sure of their age, only asking others on the ranch and inferring from the other clues, and that is a unique climate and microclimate around those posts. So i am willing to try the gravel backfill if you think it is better even on a heavy clay soil that does become waterlogged each spring with the snowmelt and fall with its heavy rains. Would the idea be to use as coarse of gravel as possible, or a blend with finer ground stone that packs tighter?

But then the next question is the posts that literally will be below waterline for at least the bottom two thirds of their planted length near the bog. Gravel must be pointless there, correct? But hopefully charring is still a good technique? i think that the environment here is very acidic so that would probably nuetralize the effect of lye...

But all the better to know that i can char green posts as i debark them to hasten the drying process, good winter work in such a dark land and with such dry late winter and spring air to finish the dehydrating process

Thank you so very much for your quick reply; i have been experimenting with charring and will probably do some more this afternoon

Hi Seth,

Can not speak to your experience with clay, other than to say that it would be strange for stone to "rot out" the foot of a post faster than clay. There must have been some type of mitigating circumstance? Clay in general is more of a concern in many regards, even over ice and frost, as many clays expand way worse. Clay also often traps water in below grade application, but clay would be better than dirt, and rock/stone better than both.

You can burn some samples to test your charr depth, but 3mm to 5mm should be consistently achievable, as you perfect you methodolgy.

You can use gravel but a large stone at the base and hand packed rock (75 mm and larger) is the best. These are pounded into place and when done well the post will not move, as it will be "rocked solid." The last stones often are larger, elongated and protruded above grade next to the post as high as 300 mm.

You can make a choice, the post in water are going to be sacrificial to a point. The wood in the water will not rot, as wood below water line can last millennia (think Venice Italy.) It is the transition zone between the water and the air that will most likely decay first (not always and that is still a mystery to me,) usually. In those locations I would probably use a rail fence and/or stone plinths method as earlier described.

Regards,

jay

Thank you again, Jay, i am beginning to think that you never sleep! And the measurements really help me visualize what to do, like hunt bonafide rocks of a much larger size than i have often seen used... i have seen "pea" gravel used in the past but always felt that rocks fist sized and up helped to solidify any post tamping so i have long been a fan of, but never heard the phrase, "rocked fast" But so as i tamp naturally some soil will migrate between the rocks, but the idea is to have as high a percentage of stone as possible?

Meanwhile you are very right about sacrificial on the bog, my long term plan is to actually use trees with insulators screwed into them (but screwed out a revolution of few every few years) as they will always strive to maintain a vertical and prevent rot themselves But at the moment i have to build parallel corners to meet the requirements of the predator fence...

i am feeling better equiped with wisdom all the time, thank you!

And i have been wondering even more today, in addition to over the course of the past decade, why it seemed that the posts in sand in south-central North Dakota rotted off faster. It is typically a fine sand in a rather active biome with ants and all, so there probably is much more to the story than just sand versus clay. But i can't explain it... and can only instead keep my mind and eyes open next summer when we return as usual to help for about a month. One possible theory is that this clay is a very quickly compacted sort, and these posts were pounded into the ground after a preliminary hole was reamed with a digging iron, and if needed water was added to facilitate the pounding, so maybe the clay compacts that well during the process that most air is excluded and thus decay is slowed?

I would imagine it is a type of local fungus that is in the soil or a healthy termite population. Without testing and samples, it is really hare to know...

Has anyone tried the stone/gravel back fill on a post for a building? Will it work for something that will have more lateral pressure than a fence post?

Maybe the char doesn't stop degradation if its moist, maybe what it does is stop carpenter ants and termites. I can't imagine most bugs being real entheusiastic about eating charcoal. So for siding or above ground stuff it might work fine.

Even below ground, a layer of charcoal might help stop carpenter ants and termites. Lack of big chewing bugs would probably help stop the migration of rot. Also, cooked, hardened wood under the charcoal might produce a barrier to moisure and/or fungi for a while at least. If the heating killed the fungi spores in the wood it might help.

Nick Kitchener wrote:Hmmm, I see they also sand the char back to the (fire hardened) wood.
I wonder if its the wood/charr boundary that provides the protection. Everything's about edges right?

That is a good observation. Between the charred layer and the unaltered wood is a layer of torrefied wood - super dessicated and very slightly altered. This is the fire-hardened stick stuff of our paleolithic ancestors. The torrefied layer is harder, less absorbent, and more resistant to deformation than charcoal. Sounds applicable to posts.

Real charcoal you should be able to crush and break in your hands. When we make biochar, and can't break a charred limb with a shovel edge, we call these "brands" and save them for the next fire. The cores are torrefied.
That said, I have never been able to make a satisfactory fire hardened stick point using softwood.

Hey Jay,
Anyway you can private message me so I can discuss more about charring seeing as you seem to know a lot and I am new to this concept.

Thanks,

Jay (also my name LOL)

I currently have painted cedar siding on my house. I need to change some windows and want to add insulation to the exterior and will be removing the siding. If I can take it off and keep condition can it be used in some method of charring or Shou Sugi Ban and reinstalled? would the paint need to be removed? Any particular steps or approach needed. Very new to this so thanks for any thought and/or advice

I would think removing the paint would make sense. Although you could try both ways and see if it works. As long as the wood is charred it should work.

Degradation of wood is a surface area phenomenon.  Ultraviolet light will degrade wood.  Oxygen will degrade wood.  Water will degrade wood.  Where water and oxygen co-exist tends to be a place where rapid degradation can happen.

Some woods will surprise you: alder has little to no rot resistance.  Apparently much of Venice, Italy is supported on alder poles.  I would guess they are continuously submerged, and there is little or no dissolved oxygen in the water.

Some woods have pores in the wood.  Oak is notorious for this.  Paper is porous.  One of the earliest "modern composites" work revolved around making honeycomb out of paper, and then impregnating the paper with phenolic resin, and curing it.  And then impregnating it again and curing.  And this impregnation/cure cycle was repeated to some point.  One way of looking at this, was this cycle was repeated until the pores were filled with phenolic resin.

What is wood?  Wood is a cellulose fibre reinforced composite where the resin part is a copolymer of hemi-cellulose and lignin.  Lignin is somewhat similar to phenolic resin.

Drying oils (like flax oil) are typically unsaturated, and in drying they crosslink.  Being oils, they had little solubility in water to begin with.  Once cross-linked, they probably have little solubility in simple organic solvents.  So we could take a piece of oak that is porous, soak it in flax oil, let it dry out, soak it, dry out, soak it, dry out, to the point where all the pores are now filled with some polymer derived from flax oil.  What that gains us, is a huge decrease in surface area per unit mass of the oak.

I believe most of the different between white oak and red oak in terms of rot resistance, is a surface area per unit mass effect, as the red oak tends to be porous and the white oak doesn't.

Some reports are on charring wood.  I think I've seen treatments based on putting posts in "hot oil".  Both are exposing wood to higher temperatures.  If the temperatures get high enough (which they would in charring), some decomposition happens.  This may introduce active sites, from which  cross linking can happen.

If a person was to bury a piece of charcoal, how long would it last?  Someone should know, after all what is biochar?

Is there any way for a bacteria or fungi to get energy by attacking charcoal?  If charcoal was just carbon, I don't think so.  But a bacteria or fungi might decide to attack charcoal if there were soluble ions present, or sulfur, or ....

Case hardening might be part of the answer in charring.  Cross linking may be another part.  Yes, they will vary with tree species as pointed out by a purely physics effect in oak.

The most rot resistant wood in my part of the world is tamarack some kind of larix, a deciduous conifer.  I am going to guess that black locust and osage orange will typically outlive tamarack by about 2:1, but I would not be surprised if there were environments where tamarack will outlive black locust and osage orange.  All of these woods have constituents to try and reduce attack by fungi (probably mostly) and bacteria (probably not as much).  These constituents will have different concentrations and possibly locations between bark, sapwood and heartwood.  But by and large, all of these woods are resistant through and through.  Pressure treated wood only treats the skin, with something that has not been tested as long as mother nature has been testing tamarack, black locust and osage orange.  If a pressure treated post could never crack in service so as to expose untreated wood to the environment, it would probably last a long time.  But this also means people that cut or drill holes in pressure treated, treat all newly exposed surface.

I will still put my money on tamarack, black locust and osage orange.

As I understand the borer that can infect black locust, what one ends up with might be something similar to red oak, lots of pores and surface area.

People have to stop relying on the Internet as the absolute answer to everything. I like to rely on old timers and what was done way back when. Another good source is the Amish if you have any around you. I know in upstate New York they are a great resource for woodworking and carpentry.

Jay C. White Cloud wrote:Embrace the nature of things, don't fight against them, you will be more at peace with your craft if you bend to "it's will" than trying to make it bend you yours.

I feel this statement holds true to everything. So many times we have a preconception of what something “has to be” that we overlook the natural beauty of what it can become. Your greatest teacher is the natural world around you. Happy accidents can become beautiful results if you sit back and really listen to what the piece is trying to tell you. We are all artists...

🏔🙏🏼🏔

Hey everyone, I just came across this site trying to rediscover what my grandfather did 85 years ago in the hills of North Ga with his fence post on our family farm. There are many of them that are still in great shape and I have had to replace most of the modern post I have used after 5 years. I am an old hill-billy that doesn't care to much about the hole naturalist movement that's going on I just wanted to build a good fence that will last cheaper than buying more wooden post that will rot out in a few years. I know he used oak b/c that's what he had, and I know he burned them to keep bugs out (termite, and whatnot) and I know he soaked them in oil and salt with a coat of red clay painted on after then reheated to harden the clay but that's all I know. If there's anyone who may know more about this I would appreciate the info. Thanks

> fence posts

Any idea how your grandfather did that treatment stuff _quickly_?   Fence posts can add up fast.


Regards,
Rufus

Hi Rufus
Unfortunately I do not.i know what you mean about the price and that's why I'm working on figuring out how he did it. My grandfather passed away when I was Ayoung and my mother never cared to learn building skills from him.
   I am trying to recreate the process and if I think I get it right I'll leave a message on here but until then if anyone else knows anything about it I'd appreciate the info.

Actually, I was concerned more about time than co$t, but yeah, it all adds up.

Best luck,
Rufus