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Posts in the ground, make-em last ideas  RSS feed

 
Posts: 18
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Hi Everyone,

I want you to blast holes in these ideas...please. But before you do, please research and be able to back up any criticism.

So I want to do a house similar to Mike Oehler's but a little more refined. My wife "needs" a few niceties if she is going to leave corporate America for good.

I've been thinking about posts in the ground for a while now. Here are my thoughts:

Use 12X6X6 heavily treated lumber sunk about 4 feet down. Before sinking, paint on 3 coats of coal tar epoxy using a respirator.
Put a little bit of Secure Set post setting foam in the hole and put the post in. Let the Secure Set do it's magic while keeping the post level in the x,y plane.
Fill about 2 feet of the hole with concrete or gravel. Potentially just fill the whole hole with Secure Set while using a biocide like Vanquish 100.
Use Secure Set to fill up the remainder of the hole and six inches above grade.
You have treated wood that will not leach preservatives.
You have a coating which is a potent biocide and waterproof
The closed cell foam is also waterproof so it further protects the end of the post and part of the post coming out of the ground.
No water, no air, no food....post should last a long time.

Now for the objections:

Premise 1) Coal Tar Epoxy is so hazardous it is being phased out by the government.

Coal Tar Epoxy phasing out was attempted but there is no cheap alternative to it's use. It is only harmful when it is in a liquid state and therefore should be applied out of doors with a respirator. Coal Tar Epoxy is an approved coating for potable municipal water systems. More than likely you have consumed water from a pipe coated internally with coal tar epoxy.

Premise 2) Foam can't support a building

Foam has been used for decades to prop up concrete structures and roadways. It has at least 4X the compressive and shear strength of soil. What will fail first, the foam or the soil under these circumstances?

Premise 3) Fungi have been found to be able to use polyurethane foam as a sole source of energy

These fungi are quite rare and located in the Amazon rainforest. They actually prefer other foods over foam anyway. Given a choice of "regular" food and foam, they'll chose "regular" food.


OK folks, what am I not thinking of?
 
gardener
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Are these posts in the middle of a floor plan or are they along the exterior?  If along the exterior are they in contact with soil or shoring above "grade"?

My initial thought is that if it's in a dry location like within the building envelope, you may not need nearly as much prevention.  Foam or rock at the bottom of the hole, untreated post, surround with tamped sharp gravel, done.  If there isn't water touching the post, no problems.
 
pollinator
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Way overkill. If you are using pressure treated, why do the extra waterproofing steps? My vision is that the board won't breathe. Moisture will get in the post, your waterproofing will severely slow it down from drying out. Pressure treated has been used for decades. I have a house on stilts on the coast. Best i can tell is it was built in 1981. They drive them deep cause of the sand (mine are 8ft deep and 8ft high, 16ft total.  Nothing else is done. In fact, they tap them in, not even digging a hole. So nothing else exists like gravel, concrete,  etc.

Ill add that hurricane harvey hit my area with 75 mph winds. If it was rotted underground the house would be on the ground.
 
pollinator
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I agree with what the other have said. I use pressure treated fence posts and they last 30 years!! That is not bad considering how tiny they are.

I would spend far more time on the difficult design portions of your building rather than on this.

I also caution you, or anyone to fall into the trap of, "Paralysis, by analysis." There is nothing wrong with developing a good plan for anything you do, but at some point it can really be over-though becoming self-dfeating. I think that is coming into play here. Don't reinvent the wheel, start gathering products to build the wheel, or even better, start building the wheel.
 
gardener
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wayne fajkus wrote: My vision is that the board won't breathe. Moisture will get in the post, your waterproofing will severely slow it down from drying out.



This. Water has an uncanny ability to find it's way into the tiniest crack, gap or space. Even wood set in concrete, water can migrate through the wood fibers deep into the concrete and it'll never dry out. Wood that stays wet rots, even pressure treated can be compromised in less than 20 years. I've seen it with my own eyes on a deck replacement job I did 5 years ago, and the pressure treated 4x4's set in concrete had failed because they stayed wet, and the deck I was replacing was 18 years old. Even new pressure treated lumber is wet from the process, and if that is not allowed to dry, it can shorten the life of the lumber. When I've built decks, I let the deck sit for six months to fully dry before going back to stain or seal it. When waterproofing, keeping water out is important, but it's also important to also give water a way to get out or evaporate. Look at old barns as an example. Often, hundred+ year old boards are in suprisingly good condition even though they get wet all the time because they can dry in the wind and sun, and there was no treatment on that wood. The boards in contact with the soil or posts set in the earth, now that's a different story. Those boards can wick moisture from the soil, not to mention all the microbes that cause the decay in the first place are in contact with the wood.
 
Jp Wagner
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Thanks everyone for your input. Here's my two cents regarding the longevity of treated lumber in the ground. I currently live in the Houston, TX area. I have to replace treated fence posts on a regular basis, probably every 15 years. When I dig down and pull out the post, even if it hasn't rained in a month, the clay soil is very damp. The wood post is damp as well as the concrete. Here it is hot, humid, and sometimes quite rainy. Wood underground never dries out. That's why I have to replace them every 15 years.

I'll be building in rural Arkansas but I don't have as much faith in treated lumber as some of the posters. The stilt construction on the Gulf Coast is interesting in its longevity. Those wood poles are treated for sure but they potentially reach the water table. Wood under water hardly rots at all due to low oxygen levels, not treatment. Think of those 1000 year old buildings in Venice. The whole place is built on wood poles which rarely need replacing. Subsidence is an issue there but not wood rot, at least under the buildings.

So yes, build the building and get it over with. I understand that concept. I'm a few months away from starting as we need to sell our house in Texas before we move anyway so this isn't a paralysis by analysis situation. I would like to leave a structure that endures past my lifetime. Wood posts in the ground, although treated, simply don't last near as long as manufacturers say they will. Does anybody have any better ideas than just stick the posts in the ground and hope for the best?
 
James Freyr
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Hey JP, you mentioned in your original post you may be mixing some concrete. Have you considered inserting sonotube in the holes in the ground and filling them with concrete to an above-grade level, and then setting any lumber on top of those? That will keep all your lumber out of the ground, ready to shed rain, and surrounded by air.
 
Jp Wagner
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I did think about it but then you not only have the expense of the sonotubes, the concrete, the rebar, but the 1/4" thick U-type connector like a Perma-column. I can't afford $200 a hole. I have 30 posts to set. That would kill my budget. Have you priced the 6x6 connectors for the top of a poured concrete pile? They are really proud of those things. The biggest problem is lateral loading. Unless the concrete in the sonotube is reinforced and then the post attached with a serious bracket, the lateral load of soil/gravel/sand will either push the pile sideways or snap it. You also have the substantial problem of spalling. The unreinforced Roman Panthenon dome is 1900 years old and in good condition. Rebar reinforced 40 year bridges are falling apart. One of the worst things ever imposed on a populace was reinforced concrete using steel rebar. This will cost trillions of dollars to repair and maintain over the next couple of generations. The practice should be outlawed. We have alternatives to the Fe/Fe3O4 cycle but we ignore it and kick the can down the road.
 
pollinator
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^^^yeah this^^^ is what i was thinking too.

or something similar like stone and concrete, or lime, and /or concrete forms/bricks/concrete blocks + rebar.

concrete forms

or even - using a method like this for any parts below ground, and no wood in contact with the ground. sort of like making concrete posts, instead of using the wood ones.

also i think with any type of underground building, you need to zoom way out to the whole site design, water flow, and also to how you re dealing with moisture and rain fall in the surrounding ground around your building.

this is why i think the  UMBRELLA HOUSE ideas with insulating and water proofing the surrounding ground around your structure, are particularly brilliant.
in that they both insulate the surrounding ground for heat storage, but also shed water away from your building.

passive annual heat storage

if you keep that surrounding ground dry, and use methods like these, it would be better if you want to be using a lot of wood below grade.
 
Jp Wagner
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You still have to attach wood to concrete at some point. Concrete with fiberglass rebar is a possibility but even more expensive. Epoxy coated rebar is another expense too. I understand your umbrella concept but what about the uphill patio in a Mike Oehler type design? Water will have to be dispersed off of the patio by using French drains. The drains will be in close proximity to the posts. You can umbrella the sides but the front and backs are the problem areas. It all comes back to keeping wood posts in the ground dry if I want any chance of staying on budget.
 
leila hamaya
pollinator
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i agree it's a pickle.
sorry for my pro concrete posting originally, we posted at the same time, and now i can see maybe you think of this as a neccessary evil, potentially. in your first post you mentioned it, and i do think for several reasons it's an obvious choice for things below grade.

but yeah i have looked into this similar ideas, how to make your own soil concrete on the cheap, how to set posts that last.

when i have built fences and such i generally use soil crete.
a few bags of cement, lime, etc, a lot of gathered sand, rocks, gravel and clay/soil/fibers or whatever else...can go quite far on a basic foundation/footings/base for an earth plaster building or post and beam on top of it.
say 500-800 bucks for all the tools, misc stuff and bags of cement and lime, others.builder's sand, sharp gravel.
add to that quite a lot of labor hours gathering rocks, sand, gravel and clay/soil/etc...and well thinking tiny house square footage...

but anywho back to the post in ground topics...some ideas i have heard are doing as you suggest, with coatings on treated wood.
i have heard suggestions of borax, tar, polyurethaneother coatings. even think some people use gasoline. diesel?
ha, i dont know but i am sure i have heard of this.

another idea is burning the ends of the posts because the charred bottoms of the posts will protect the wood and make them last longer. i have found chunks of old wood in the ground that are from burnt wood, it does preserve the wood...the charring of it makes it less penetrable to water, it repels moisture.
 
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Hi JP (and everyone),

I'm a belt and suspenders kinda guy myself, so I like the idea of going the extra mile to make something last.  We all know that it's better and easier to do it right the first time.

I've started a business building passive homes (https://CruxHomes.com) and I get lots questions that are hard to answer.  It's unfortunate, but there is almost never a silver bullet when you build something; it always depends on where you're building.  That being said, I'd like to know more about your property in Arkansas.

The things that are most likely to destroy wood are (in no particular order): insects, rot (generally fungus), repeat wetting and drying (physical damage by swelling then contracting repeatedly), salt infiltration (crystals growing inside the wood fibers), other physical damage (wind, freeze / thaw) and UV exposure.

To your point, the ancient Venetian wood hasn't rotted because there isn't enough oxygen, but your treated fence posts rot because the fungus that rots wood is ubiquitous, the constant moisture in your clay heavy soil in Houston leaches the treatment chemicals and then there is enough oxygen present for nature to take it's course once the treatment is gone.

I have to admit that I'm not 100% clear on what you're building.  Do you need 30 individual posts or are you burying a wall of logs like a Wofati?

My rough thoughts are as follows:

- Dig a trench (or hole) where you want your post(s) to be
- Compact the earth at the bottom of this trench or hole
- Pour a spread footer or line with wide stone(s) capable of bearing the load of your post(s)
- Cover the footer or wide stone with gravel
- Line the sides of your log wall (or wrap your post) with several layers of old billboard tarps
- Back fill and re-compact the earth
- Add a flashing detail to minimize surface water from entering your footings

This should stabilize your moisture levels, give any water that does get in a place to go, remove the need for a french drain, minimize leaching out of your treated wood thus maintaining the integrity of your posts for a long, long time . . . no respirator required!

If you like this idea, I'll be happy to sketch it up for you . . .

I've attached an image of a prefabbed post flashing for individual posts to give you the notion of what I'm referring to, but it would probably be cheaper to fab your own.  



I also included a flashing detail to give you a sense of what I have in mind should you build a log wall, but again if you like the idea, I'd be happy to sketch up something more specific.



Here's a what I mean by a spread footing (since it's a pretty generic term):



Here are some other references:

http://www.deckmagazine.com/design-construction/what-causes-wood-to-rot_o

https://bct.eco.umass.edu/publications/articles/wood-myths-facts-and-fictions-about-wood/

I hope this helps!
Square-Flashing-for-Individual-Posts.jpg
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Square Flashing for Individual Posts
Flashing-Detail.jpg
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Flashing Detail
 
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