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How to protect untreated wood posts for 200 years?  RSS feed

 
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I was thinking about this problem and it seems there is no solution. But maybe there is. I want everyone out there to try to see the flaws in this. Say you want to use a pine tree (or twenty of them) that are 8 inches in diameter and cut to 12 feet in length. You've already debarked them and are ready to put them in the ground but you have a nagging feeling in 10 years these nice strong poles are going to be mush. Is this solution a possibility? Take some 10" PVC pipe and cut a 5 foot section. Glue on an end cap. Put some sand in the bottom of the 4' deep hole you excavated using a 12" auger (or larger). Place the pine pole into the PVC pipe. Make sure everything is level and pour dry cement or sand around the excavation and the exterior of the PVC pipe. Fill up the interior of the PVC pipe with 150 degree melt roofing tar. The pole is protected from water for at least a couple hundred years. In an interior situation there is no way water will get onto the pine pole. It would be next to impossible to crush the bottom of the PVC end cap after it's filled with roofing tar and sitting on a bed of sand. You could even take some veneer of your choice and glue it to the one foot of PVC pipe that would be exposed if it's a problem in your installation.
 
pollinator
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What's the advantage to going this route over pouring a concrete pylon and keeping the wood above grade? I don't know for sure if your approach would work, but it does seem to be quite complicated and include a good bit of nastier-than-concrete stuff. I know for one I wouldn't want to be filling a 5' pipe with hot tar.

I'd be worried about the end cap disconnecting and PVC crushing, despite the sand foundation. A 8" Doug Fir post is going to hold somewhere in the neighborhood of 30,000lbs / 450psi. I suspect that's more than sufficient to exceed both the tensile strength of the vertical pipe and the crushing strength of the end cap and the holding power of the glue and the shear strength of the end cap. There's also going to be a lot of shearing force in the vertical pipe from your moment forces, and the question of whether the tar will be rigid enough to seat your beam in the first place.

I know of three ways to keep untreated wood preserved for 200 years:

1. Keep it dry and out of the ground all together
2. Live in the desert
3. Live in permafrost
 
garden master
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I would suggest charring the wood, but it's not as easy as burn it and plant the post. There are some great links in this post here.
 
gardener
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I think the best response is "it depends"...
What is the climate? If it is dry enough, a simple stone packing around the post which allows ventilation would do. If the soil is well-drained, the tar might preserve it well enough. It is a petroleum product (as is the pipe), though I personally think there are places where petroleum use is reasonable.
Another way to protect the posts is to keep them out of the ground. Use them in ways that don't require them to bear side loads at the base, or else build bracing to take those side loads.
 
Jp Wagner
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Thanks for the responses. These are things I wondered about too but the properties of PVC seem to exceed the requirements.

http://www.vinidex.com.au/technical/material-properties/pvc-properties/

When I think about something being crushed I think about my wife in stiletto's. Every step she takes there is in excess of 1000psi on the bottom of the heel. I think you could easily step on a flat piece of PVC with a stiletto heel and not leave an imprint. As far as the other forces, they are being dispersed over a rather large area due to the solidified tar and integral contact of the pipes exterior with the soil.

The problem with a concrete pylon, as far as I can see it, is in the connection. Backfill is going to apply a lot of lateral force on the connection. I can see either the metal bending or the wood breaking due to the concentration of all the force in one area. Instead of the forces being applied over a large area, like with with a pole in the ground, the forces are magnified in one area. There is also the expense of concrete, rebar, maybe a Sonotube, and probably a Simpson tie or equivalent. All this takes time and money, especially if you're doing 20 of them. A PVC pipe could be tarred to a pole in a controlled external environment before putting the pole in the ground. That would make the job even easier.

Still seems like it might work.



 
pollinator
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I don't think it would work very well. Part of the problem would be the boring of the hole, fence posts get their strength NOT from the bottom of the hole but the friction on the sides of the posts. In the orginal situation this fails on two fronts.

1) The PVC sleeve does not allow for much friction.
2) The sleeve/post is bored and not pounded in. As many people have found out the hard way, posts should always be pounded in and not placed into a hole that was bored out.

The orginal post also suggests that water would not get in and rot the post, that is not true at all. Surface water may not get in, but moisture will be present between the wood and roofing tar just because it is in the ground. You cannot place a post in a moist rich environment and stop it from wicking in and absorbing moisture. The tar may keep the rain out, but moisture and relative humidity will be,

....

A way to prevent this is to infuse the tar into the wood so rot is arrested. It is not a 200 year fix, but rather a 30 year fix, just like pressure treated wood. The Do IT Yourself way my forefathers used was to soak the posts in engine oil (or any petroleum product) to bury-depth, but really...do any of want to do this? We did a lot of things back in the old days I would rather not repeat. Even then it lasts 30 years. Myself I use cedar and pressure treated posts and they last 15-30 years. Considering how fast a cedar/PT post can be installed, and their cost, as even buying them is only $3 for a sharpened 6' post, they are pretty cheap. Myself I produce my own cedar ones, but have to buy PT ones if the fence is paid for by the USDA.

For those that are not okay with a 15-30 year lifespan, there are metal and concrete/wood posts that work quite well. Plastic and fiberglas unforntately break down from UV rays and last only 7 years or so before they get brittle or delaminate.
 
Glenn Herbert
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If you really want to build an underground house and have it last 200 years outside of a desert climate, you need to keep the posts away from ground contact. Gravel and stone bases and subfloor braces to resist lateral loading would do the job and allow the wood to be inspected later. It would be necessary to brace the frame so it is stable before backfilling; this could improve the roof loading capacity too.
 
Travis Johnson
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I think a lot of it has to do with wood species too. Here we use white cedar for longevity, but here is a kick in the teeth, the wood cannot take a structural load, it is weak and britttle. Hemlock is better, but is not as rot resistant.

Really it all comes back to what is available when building a WOFATI. They take a lot of wood so it means using what you got if the project is going to be fiscally feasible. If I ever build one it will be out of hemlock because I have tons of the worthless wood. My woodlot comprises of 28% of the stuff and right now no commercial sawmill is taking it. So for me, I can put all that wood into making a cheap home for my wife and I. If the longevity of it is only 25 years, BUT the cost to build it is so low, it is a win.

Let us do the math on that. I designed a WOFATI for the wife and I of around 1000 square feet that would cost around $25,000 to build. If it had a life of 25 years, that is $1000 a year in costs. Since rent here is about $1200 a month, just living in that WOFATI would have a return on investment of less than 2 years. In other words you could build a WOFATI every 3 years and still be better off than renting! Obviously they are going to last longer then that. Replace as much as you can to keep the building going, but at some point the occupants are going to want to change things up and start another WOFATI anyway. Perfect...the first one has served its purpose.

Now sure I can build a WOFATI that will last 200 years, but for me that is not the attribute of a WOFATI that I want, I want a cheap home that I can build without a mortgage, because lets face it...no bank is going to float a mortgage for one anyway.
 
Jp Wagner
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Thanks again for all the responses. I didn't do any research ahead of time and Travis has brought up some good points. Travis, it seems as though you are under the impression that PVC pipe is slippery when in contact with soil. I was a science teacher for many years and physics doesn't lie.

http://www.macplas.co.nz/mechanical-properties/

I do agree that a bored hole is less desirable than a pounded in pile but by using an abrasive intermediate like sand or concrete, a lot of that benefit can be gained back. You can also have the bored holes belled out at the bottom to increase the surface area. If you have decent soil to build on, and enough posts, subsidence should not be an issue.

I'm not really sure what you mean by moisture being above the tar. The hole would be 4 feet deep while the PVC pipe would be 5 feet long. There would be 12 inches of pipe above the soil line. I agree all air has moisture content but I doubt enough to cause rot, especially since the posts would be indoors if built like mike oehler advocated. A treatment for humid conditions can be easily formulated with a glycol/borate solution. It adheres chemically to the cellulose in the wood and would last indefinitely unless washed away by liquid water. Does anybody out there know how long you would have to submerge green wood in a glycol/borate solution for full penetration? I can't seem to find that info anywhere.

Glenn indicated to make a structure, or at least the foundation, last for 200 years it requires no ground contact. I don't see how a system like this would have any ground contact. You have structural wood inside of a sealed plastic pipe a foot out of the soil and surrounded by tar. I still don't see any reason why this wouldn't work.

I understand we want to build a cheap structure but why not try to build one that will last several lifetimes if it only takes a few extra dollars?
 
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Too bad the American Chestnut is no longer around.  I have seen fence posts that were installed in 1935 that are made of Am Chestnut that are still standing and are still sound along with many cabins and tobacco barns made of the stuff that are still standing and sound.  To my knowledge the next best wood for ground contact rot resistance would be black locust.  I personally wouldn't want to use the PVC.  Biggest reason, is cost.  Have you priced really large diameter PVC pipe?  Another reason is that it would be difficult to get a "perfect" fit of log to pipe without a good deal of work.  I would assume that you wouldn't want a lot of play between pipe and log.

Here in Alaska, When I put posts in the ground I go 4 feet deep then wrap the post in poly plastic before backfilling.  Four feet deep to get down below frost line and the plastic to keep the freezing ground from grabbing onto the post and frost heaving it up out of the ground over time.
 
Jp Wagner
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Yep, if you try to buy the stuff new from a supply store the stuff can be pricey. It shows up all the time though on places like Craigslist. A contractor bids a job and buys a little too much and needs to unload it because it's taking up too much room. You can buy it for about 10 cents on the dollar. Contractors can't use it for new jobs because the stuff gets damaged by UV and goes out of spec. For our needs the pipe is perfectly fine still. They either chunk it or sell it for next to nothing.

No need to worry about frost heave here in Arkansas. Sizing to reduce slop inside the pipe could be a little difficult but not too hard to manage. Still think it might solve a lot of problems.
 
Glenn Herbert
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I presume your posts are not kiln dried... so they will have plenty of water that will be sealed in by the tar. It may be that the outer layer will not rot, but the inside will not be protected. Even if it does not get wetter, it will not dry out.
 
Travis Johnson
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I think this is an issue of practicality versus that of theory.

I am not trying to be argumentative on this, but "cost slightly more" is a huge understatement. I have built several homes from scratch and currently own three houses and my experience has been that costs escalate very quickly when building homes...very quickly. Another aspect that is often unaccounted for is that before Z-task can be done, X and Y must be done first for that to happen. That means relying upon such things as Craigs=List finds can be very difficult. In short the theory often is I am just going to build my home as I find the products I need, but reality often is, if this does not get up, the rain will come in and fill my work area with a foot of water. Yes there are some amazing scores on building material that can be had, but I think it would be silly of me to rely on them.
 
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I was curious about how long the PVC will last before breaking down.  One reference said 75 to 100 years.  I wouldn't have thought that long.

My thought about it though, is that when PVC breaks down (and it will eventually) it is still not biodegradable whereas untreated wood could rot away without much of a trace. 

https://www.greenlivingtips.com/articles/pvc-and-the-environment.html

PVC’s durability is also its downfall environmentally speaking – it’s not biodegradable or degradable. Items made from PVC will retain their form for decades and the breakdown that occurs is just granulation – the pieces simply become smaller.

 
Jp Wagner
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Hi Travis, absolutely not being argumentative either. I just figured I'd put the idea out there and have people shoot holes in it. As a community we need to brainstorm to build better and cheaper.

I just looked up on Craigslist Memphis and found three folks selling 10" PVC pipe. One guy (or gal) has 900 feet at $2 a foot. I'm not saying you could buy this stuff every day of the week like going to a store but planning ahead a month or so shouldn't be a problem. End caps could be a problem but you could buy a flat sheet of 1/2" PVC and cut out circles. Get yourself a hot air plastic welder and you're done. There was some other person selling 10" underground aluminum water pipe in 30' sections for $100 each. The stuff has a minimum service life of 100 years. If you have a plasma cutter, tig torch and an AC welder you would be good to go too.

All I'm saying are there are options to do something a little better and last a lot longer, for not too much money. I'd rather put up an extra $1000 and not have to worry about a rotten foundation.

I understand what Glenn is saying about the wood not drying out. Wet wood is not really an issue as far as I can see. You don't see a whole lot of healthy trees just falling over from having wet wood. Also, wood under water almost never rots. Look at Venice, Italy. They have underwater pilings there over 1500 years old holding up those buildings. The above ground masonry buildings rot before the wood pilings go.

Still seems like a viable plan.
 
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Would a living fencepost be an option?

I have rammed fresh willow posts in our garden one year ago and they have grown into small trees by now.
 
Jp Wagner
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Hi Judith,

Looks like we're going to be neighbors, kinda. We just closed last week on 18 acres in the Ozarks outside of Eureka Springs. Stuck in Memphis right now until we can build and get out of the city.

I hear what you are saying regarding the environmental impact of PVC. I don't mind the use of fossil fuels for durable goods like PVC pipe. Over its lifetime the amount of damage it will do is, in my opinion, minimal. You probably do more damage driving to the grocery store than some underground plastic pipe. We are all living a life where our footprint is of concern. Every thing we do seems to all revolve around fossil fuels. Right now I can guarantee you are either touching or using something that was manufactured by using oil as a raw material or from the energy expended by burning it. We simply can't get around it.
 
Travis Johnson
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Wood submerged in water, or wood embedded deep into the ground is not much of a problem because there is not much oxygen to cause decay. It is the area that gets wet and dry that rots out. So for a wharf pile, it is where the tides work, or in a soil embedded post or pile, within inches of the surface or below the surface of the ground.

I am not sure I would cite Venice as a success though, they are sinking at a rate of a few inches per year. That is a lot. I suspect that city endured what an old building of mine endured. Sitting on rotted posts, the weight of it kept the building pressed on the soil and over the years as the wood rotted away it just settled lower. the building did not move, look out of place, or ruined, it was just a lot shorter in headroom. Theoretically a WOFATI with adequate headroom could do likewise with no issue for many years.

I suppose those in more populated areas would have access to more material than I do here in rural Maine, but some other difficulties could arise. I have no building codes here to speak of so that helps in the building of a WOFATI, and we have one of the lowest crime rates in the country, so the thread of receiving stolen good obtained on Craig's-List is a lot smaller too.
 
Judith Browning
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Jp Wagner wrote:Hi Judith,

Looks like we're going to be neighbors, kinda. We just closed last week on 18 acres in the Ozarks outside of Eureka Springs. Stuck in Memphis right now until we can build and get out of the city.

I hear what you are saying regarding the environmental impact of PVC. I don't mind the use of fossil fuels for durable goods like PVC pipe. Over its lifetime the amount of damage it will do is, in my opinion, minimal. You probably do more damage driving to the grocery store than some underground plastic pipe. We are all living a life where our footprint is of concern. Every thing we do seems to all revolve around fossil fuels. Right now I can guarantee you are either touching or using something that was manufactured by using oil as a raw material or from the energy expended by burning it. We simply can't get around it.



Eureka is a great part of this state...good for you!
I get what you're saying and agree, it's difficult to get away from fossil fuel products.  I like to go through the mental exercise of trying to find ways to do without them though.  I understand that this hypothetical PVC in a wofati would be doing no damage for most of it's life.  It's knowing that eventually it breaks down into tiny bits of plastic and joins all of the huge amounts of other tiny bits of plastic in the world that worries me.

I like the idea of using aluminum pipe for your idea even at the added initial cost.
 
Jp Wagner
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Venice is not sinking because of wood rot. They've tested the pilings and they are still perfectly fine. The problem is the ground the city is built on. They put a bunch of heavy masonry buildings on very poor weight bearing mud. Over time the compaction of the mud is getting the better of them. Also, until recently, they were pumping a lot of water out of the ground. The same thing happened in Houston, TX where the entire city inside of the 610 Loop was about 3 feet lower than it was a few decades ago. Venice also suffers from basic plate tectonics. It's in a subduction zone where it will eventually end up under the Eurasian plate.

A really cool example of wood being preserved is the wood at the bottom of Lake Superior. It's been down there for a LONG time.
 
Jp Wagner
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Oh, forgot to mention that Venice is not sinking quite that fast. Most estimates put it at between 1-2mm a year. At that rate is takes a little under 20 years to go down an inch. I would hate to see that city go under water. It is one of the most amazing cities on Earth and a blast to visit.
 
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The best way I've found is to NOT put the post into the ground, but to set it atop a rock or similar non-porous surface.  Here's a short video on how to do it.

 
pollinator
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I am with the school of thought that suggests that if it needs a lot of extra care to be put into the ground, then maybe that's not where it belongs.

I would use the posts for structural roofing material, or as uprights, but atop a masonry piling where it is socketed. There's no real mystery why most ancient structures still standing are masonry and contain little intact wood, except in certain circumstances. Keep it out of the ground and away from even the possibility of getting wet. I intend to use compressed earth block or rammed earth pillars in my build, but I would like to be able to have cattle graze atop my roof and not worry about it, as well as perhaps a forest, so there are other reasons.

But as to preserving wood you can't be talked out of putting in the ground, I am with the cedar and black locust folks, and depending on the situation, the living willow post one too. I am intrigued by the concept of charring to eliminate the volatile organic compounds that feed decomposition, as seen in Shou Sugi Ban, a japanese technique that exemplifies this. I have often thought that if the charring could be done slowly, and under specific temperature, pressure and oxygen conditions, like that of a purpose-built biochar retort, then perhaps the wood could retain more of its structural properties.

I have also thought of a different retort process, but one based on the process that creates aerogels. These are gel products that are saturated with supercritical carbon dioxide, which replaces the moisture content, and later evaporates, leaving a highly porous foam. The composition of the gel determines the specific properties of the resultant product, but its current uses include insulation for orbital vehicles and satellites.

So basically, I was thinking that the moisture could be expelled from the wood, along with the volatile organic compounds, which would be boiled away in the supercritical CO2 (at least I think that's what's indicated). In a second-stage process, something could even be injected to replace the moisture, much as with pressure-treated lumber, but I don't see the need, personally, unless it added enhanced structural properties. The CO2, incidentally, could be cycled in a closed loop, such that pollution wouldn't enter into it.

Personally, I think the retort for slowly eliminating volatile organic compounds for an effect like Shou Sugi Ban is the most appropriate technological solution to post preservation as it could be done at the homestead level in many cases. Practically speaking, though, a retort is unnecessary. You can just char sufficiently dense hardwood very carefully. Fire can be used to harden wooden spearpoints, so I don't see why its careful application wouldn't do that to a sharpened post end.

-CK
 
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wet wood rots because of oxygen feeding the microbes, or what ever eats the wood.

wood submerged in water is in a low/no oxygen environment, so lasts a long time. 

in my area, fresh cut trees were layered into swamps and rocks/gravel poured ontop to hold them down, and roads built on them.   In areas where there was always standing water, those trees are like the day they were cut.

in areas that were intermittent, they were rotted in various stages, depending on the clay sealing around them.
 
pollinator
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Mr Chickadee just posted a video on scribing post to rounded stone



Some pretty impressive fitting to the stone. Plus he not only chars the post but then treats the post with pine tar/turpentine/veg oil to seal them.
 
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Jp, can we go back to basics?
What are you actually trying yo achieve?
 
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