Jp Wagner

Hi Everyone,

I have a question that I can't seem to find the answer to. A rubble trench foundation seems to be ideal but there is a problem with them. They incorporate a French drain along with the foundation trench. (See Pic) The problem also arises when dealing with a permanent wood foundation with plumbing lines. How do you provide support for the building above (via compaction of the foundation material) while not damaging the 4" PVC drain and allowing proper drainage? Contractors who deal with backfilling problem basements after putting down drain tile would never use compacted gravel around a PVC pipe. Most would say to use compacted soil free of stones but that would completely plug up the French drain. Permanent wood foundations usually cover the plumbing lines with 6" of gravel and then use a plate compactor. Since most plate compactors are not that big and only apply a limited amount of force I can see damage to piping being not a big concern. If I was using a Jumping Jack in a rubble trench that PVC pipe would be toast.

Thanks Y'all

Hi Everyone,

I'm getting ready to start a small 1000 sq. ft. building and I tried Googling this but to no avail.

Instead of using large timbers spaced 8-10 feet apart, I plan on using 4x4's on 4 feet centers. Basically the construction will be similar to a pole barn. According to Cornell University...https://courses.cit.cornell.edu/arch264/calculators/example7.1/index.html...the 4x4's should be more than sufficient given the weight bearing capacity of the soil, the number being used, and the axial, uplift, and lateral loads being applied.

The question I have is this:

Has anybody ever put the bottom 3-4 feet of a treated 4x4 inside a piece of 6" schedule 40 PVC pipe with a solvent welded end cap? Either fill the internal and external voids with cement or some "Secure Set" post foam? Since the posts will be behind fiber cement siding and protected from the weather, moisture intrusion and UV exposure should be almost zero. Heck, you could even fill the post/PVC void with octoborate and the system would have multiple levels of protection, especially if you used spray foam on the top to seal out moisture. When you do the math for the compressive strength of PVC it far outstrips the bearing capacity of the soil, even with just end-loading. The lateral strength is also well within specs when filled. Also, the frictional coefficient of the PVC is far in excess of any uplift issues. Despite what most people think, PVC is not very slick from a physics standpoint. The cost is minimal if using standard 6" pipe and end caps. The cost per post would come in at roughly $15. Things like permacolumn or any kind of concrete piling with a post base end up being way too expensive and have a problem with lateral loading at the wood base. I plan on furring out the front of the 4x4's to give a flat treated wood surface to nail on the fiber cement siding.  

From what I've personally witnessed, over 100's of times in the Houston, TX area, are ground contact rated 0.6pcf CCA treated 4x4 posts rotting out in under 20 years. I can't imagine the newer wood preservative formulations would fare any better. This was not an isolated case of a post or two rotting out but an absolute certainty 100% of the time. It never mattered if you put gravel at the bottom, used gravel instead of concrete everywhere, sloped the concrete, blah, blah, blah....the damn things rotted out 6" above and 6" below grade. Houston has got several feet of clay and moisture will stay in the hole for decades no matter what you do. I have zero faith in the studies done by placing treated wood in the ground and looking for failure. My guess is these studies are sponsored by the Wood Preservative Association or something to that effect.

Does anybody have any practical knowledge of why this won't work? Please shoot as many holes into the idea as you can. It's much better to look like an idiot here than have a decrepit building a few years down the road.

Thanks Y'all

No apologies necessary at all.

I simply don't know if a stump can be treated in-situ and what effect it would have on its decomposition. The only way to find out is to do it. The problem is I'll never be around to see the final decomposition if it takes longer than 30 years.

Hi Everyone,

Thanks for all the input. My only thoughts on concrete are that it's not near as long-lived as people think it is. The Pantheon in Rome is a great example of how long un-reinforced concrete will last. NACE recently calculated the cost of corrosion to be 2.5 trillion dollars annually. Unfortunately a lot of that corrosion is inside concrete. As a society, we have gambled on the undying strength of reinforced concrete. We have been stupid enough to put normal carbon steel in most of our concrete. If we had used 304 or 316 in all of our structures we wouldn't have the crumbling infrastructure that we have. Studies show the addition of stainless rebar over carbon steel only adds 15-20% to the initial cost but dramatically increases longevity. We have kicked the can down the road again to our children and grandchildren.

I was thinking, for rural applications, a good sized shed could be put on top of treated stumps and built for practically nothing. So what if the shed becomes unstable after 30-40 years? They are pretty much disposable anyway. I certainly wouldn't use it as a foundation for a house, at least not until many sheds have been built so we see what happens. There is a lot of incentive in the capitalistic society we live in to suppress any change from building codes. Building codes are necessary but they are also written by engineers, architects, construction firms, lumber suppliers, and politicians on-the-take. They all have a vested interest in staying in business and making sure houses are built at $150 a square foot, or more.

My vote for the cheapest foundation is a rubble trench with integral French drain. All the benefits of concrete plus drainage and no steel to corrode. Build with a PWF superstructure using .6lb CCA for the footings and maybe the first 2 feet of walls. If building underground you can either use a wood floor or 48" galvanized mobile home auger anchors for lateral thrust with the full height of walls made from CCA lumber. There are lots of ways to build without concrete and not have to dig holes and have the rebar rust inside causing failure. Just remember that concrete is porous, not only to water but to air. You mix air, moisture, and iron and you eventually will have a serious problem. Iron oxide takes up more space then the iron it replaces. The expansive forces are immense and will destroy ANY concrete, no matter how strong it is.  

Hi Abe,

How were the tree stumps treated in that 2 story house? If they were untreated, as I suspect, 20 years shows this could be a promising building technique. The studies of untreated vs. treated wood posts in Mississippi and Oregon show about a 10 fold increase in longevity. That's the main problem with new building techniques. In order to get a good idea of utility, a lifetime is usually required. By the time you figure out if it is viable or not, you're dead.

John

Saw this old thread and had a few ideas. Why not cut off the trees to the desired height and drill 4-5 1" diameter holes straight down into the stump about a 1-2 feet deep. Make up a solution of borate and polypropylene glycol and fill them up. If the tree was alive when cut, the pathways from roots to the trunk will be fully active. The solution should seep down into the roots with time. Since the building above will stop most of the exposure to water, there should be minimal seepage of the borate from the now preserved stump. Strip the bark with a power washer and surface treat the stump. You could even provide copper or stainless metal tubing which would be hammered into the holes for periodic addition of more borate solution. The metal tubing would be installed too high and cut off flush when the final flooring was installed.

john mcginnis wrote:

"Hi John,

You are mostly correct about the fence posts and rot but not for the reason you think. The posts are fine underground since they are not exposed to a large amount of oxygen. They will eventually rot as there are anaerobic decomposers but they are not nearly as efficient as aerobic ones. The post from 6" underground to the bottom of the post can have a lot of moisture and that's not really a problem. What you can't have is moisture and oxygen together. ..."

I think you made my point without realizing it. If you had two variables to control, oxygen or water, which is easier to accomplish? Water denial would be the obvious choice.

Do posts fail as I have described? Sure do, after about 20yrs or so which is acceptable pattern for me. For a housing structure probably not however which is generally why other techniques are used for ground contact -- the most common being 'Don't even try'. In my area there are several historical settlers homes that still exist. All of them are using either a stone foundation or brick as pads for joist and frame construction.

Water control depends on your location more than design. It's real easy in Arizona and almost impossible in Oregon. Eventually things are going to get wet. The only thing we can control completely is the food aspect. We have to remove the food source from the equation then we don't have to spin our wheels trying to control moisture. Granted, it can be done but I've never seen it done successfully with untreated wood in ground contact.

To your point, plinth blocks and other methods to get the wood out of harms way is the way to go. I'm trying to figure out the simplest, cheapest, and longest lasting way to get'r done. I'm leaning towards concrete piers with stainless steel rebar welded to brackets to hold the timbers above ground. On the inside of the brackets I'll weld some truss nail plates then bolt everything together. The truss plates will transfer lateral load to the metal plates, rebar, and the concrete piers. I need to use about 30 12X12X12 timbers. These are about $30 a linear foot if I buy them. They are almost free with a chainsaw and a buck in gas. I can't afford 10K+ just for the timber supports. I'll try the treatment I mentioned to start this post (pun intended) for the internal non-load bearing walls. That way if I need to go back and switch something out it won't be a structural issue. I'll still bore holes in the 12X12's and fill them up with borate though. That way I'm protected at least up to 4'.

Is the wood necessary for a test? Meaning, if you combine the two ingredients in a jar, do you get actually even get Colemanite? How quickly does that occur?

How much longer would it take for this to happen in wood when you have separated the two components and they have to "meet in the middle" to react?
Assuming that's what happens, does that "middle area" where the reaction happens retard/stop further migration in either direction? making complete "colemanitization" of the log slower/difficult/impossible? I'm reminded of a concrete waterproofer called Xypex, which forms crystals in the voids of a concrete matrix, sealing it up.

Would a treatment be "quick" as in days or weeks, or longer, like a year or more for a large log? However long it takes, the log will need to be wet... is this a race between rot and preservation?

You say a 36" deep bore in the log, is this just considering the fully buried portion to be at risk? What about the earth-facing side of the wall?

The reaction between boric acid and calcium hydroxide is very quick. The Colemanite will precipitate out as a solid almost immediately. As far as everything else...who knows? My intuition tells me the Colemanite wouldn't be a continual solid but more like a matrix with a lot of holes. The holes should allow passage of water which will contain calcium hydroxide. As far as rate of reaction, it would depend on the species of wood and its initial water content. Diffusion outwards would probably be more rapid since the polypropylene glycol would seek out moisture in the wood and aid in the diffusion. The surface of the log would have to be surface treated with borates to stop the preservation/rot battle. For total reaction I would guess at least a year, depending on wood type, initial moisture content, and external moisture intrusion. There are a lot of guesses in all of this.

Another idea would be to add some boric acid to the lime concrete mix. That way you would have a constant supply of slowly dissolving Colemanite to eliminate any chance of rot until the process of "Colemanization" is complete. If enough boric acid was added to the lime concrete you would essentially have Colemanite concrete. You could make the binding agent in the concrete Portland cement and use the slaked lime and boric acid as additives. 20 pounds or so of Colemanite in a 400 pound concrete mix would make that pole pretty much last forever. You could add an excess of slaked lime so the diffusion reaction and "Colemanization" of the post could continue. I'm pretty sure the American Borate Company sells Colemanite directly for use as a fertilizer. Heck, just mix it in directly with the concrete and maybe be done with it. Maybe you could even get a nice deep bucket and put it in the excavation and backfill it with gravel or sand leaving the bucket empty. Then put in the post and Colemanite concrete. At that point who cares if it gets wet and soaks the post. The Colemanite will leach into the post and by capillary action protect the post for probably a foot or so out of the ground. There are a lot of things to try.

Jason Hernandez wrote:

Jp Wagner wrote: IWhat does work are pressure treatments, creosote, and napthenate.

One thing I still don't understand: if creosote forms wherever wood burns (hence the creosote deposits in chimneys), why isn't it considered acceptable in organic applications? The earth is full of fire-dependent ecosystems, which, presumably, would be rich in naturally-occurring creosote.

Hi Jason,

If a natural fire rolls through an area it's there for maybe a day or so. Also, it has access to a lot of oxygen so combustion is practically complete leaving only ash. In a fireplace you have incomplete combustion so all the nasty parts of the wood don't actually get burned but build up, year after year, on the walls of the chimney. This is all the byproducts of combustion that are normally the oily residue. It's full of nasty stuff like benzene, toluene, and many other cyclic aromatic hydrocarbons. Any heavy metals the trees ingested in their lifetimes end up sticking to the creosote too leaving a really nasty chemical concoction. This stuff is toxic to all kinds of life including humans. All wood has some oil in it. It is required for cell structures to survive. When a tree dies these oils remain, locked inside cell walls. When we burn the wood we release the oils and they burn but not completely. The incomplete burning process provides enough activation energy to turn these normally innocuous oils into the life-killing thing we call creosote.  

Ben Waimata wrote:

Jp Wagner wrote: I'll have to figure out if I actually have formed Colemanite inside of the wood somehow.

Assuming you achieve this, what do you expect will happen to the workability of the timber? Chainsaw blades, drill bits etc?

Hi Ben,

In a real world scenario, the post that had been converted into the Colemanite would be underground so there wouldn't be any workability problem. The moh's hardness is only 4.5 anyway and the Colemanite would be dispersed throughout more like a very fine dust, not a solid rock. It should augment the cellulose but not replace it. In every day use you probably wouldn't even know it's there.