motor oil to preserve fence posts?

As the Original Poster I'll toss in here

I was quickly talked out of the idea and have begun some selective cedar harvest (letting more light to the plum trees) and split these for replacement fence posts as the treated posts that were here when I bought the place rot out, what to do with the treated posts is a whole other problem, but as the toxins are probably here I will most likely use them as far away from my garden as I can

     Fence posts typically rot away just below the surface of the soil. This is the most rich and biologically active layer. No matter what species of wood you use you'll get more life from your posts if you fill the hole with rubble rock rather than with soil. Put a few good-sized chunks in the bottom of the hole then prop your post up perfectly and fill it to the top with rubble. Your post will be suspended in relatively dry conditions unless you have an extremely high water table. This method of post instalation has another added benefit. It creates a perfect home for some lizards, snakes and other beneficial ground dwellers who enjoy a well drained spot out of the sun. I have garter snakes and alligators lizards who enjoy this environment. If your land doesn't contain much rock your posts will still last longer if you put gravel around just the top 3 inches or so of soil.

donno if that will help me

my water table is about 4" below the surface for a lot of the winter (even though I live on a hillside a few hundred feet above the river it rains that bloody much)

Creosote used to be made from conifer sap, nowadays it is  a chemical cocktail. Apparently if you heat conifer wood in a crucible or burn it in a hole in a bank yu. I'm told that the soot that clogs my chimneys when i burn pine is creosote.Sometimes my chimneys drip black stuff. I looked for more info online but just found the  oil recipe you described. Here people used green walnut extract as wood preservative.

I like to think  my fences will be hedges one day.  Folk here use dead brush hedges a lot. Not totally goat proof but with luck can encourage brambles, hawthorn etc.to grow 

Wire and nails in trees aren't nice

just as a matter of curiosity   did you check out the  video Paul made of the fence made from pallets  on Vachon Island?  Nothing to go IN the ground so nothing to worry about as far as that goes, and the price is definitely right, and it can be moved..you could always dismantle some and use the planks to make a solid barrier at the bottom if needful but the lady with the fence keeps goats in with it. Some pallets are already solid but they tend not to be as common.

Don't know how high it has to be..another sort of fence I have made with pallets is simply to nail 2x4s at the back and prop the pallets up side by side..it ends up not quite as tall of course, and sloped away from the field..I run a hot wire along the top of it sticking into the field a little. . Very portable but you need to have a pretty fair lean to make sure any particularly high winds from the wrong direction don't blow one or another section  over. Less of a problem with the heavier pallets, than with some of very dry and light, nicer to handle but less skookum.

I've been thinking that they might make great little windbreaks as well for young trees..or a hedge!...or...

If you had LOTS  of pallets you could use another pallet instead of the 2x4 prop and hinge it at the top with something like pieces of nylon webbing from an old outside chair, so your fence is an inverted V..they would never blow over then!!but some of them at least would likely become a 2 person job to move.

I have access to a fairly regular supply of scrap 4' tall 2x4s so this works pretty well for me. Otherwise you could always dismember pallets and use those 2x4s..you did say you had time rather than money....

considered pallet fencing, but don't have a supply near by. I've used sort of hurdle sections 1-2m long which were similar, and can be moved easily but didn't look so good. I'd used scrapwood. My neighbour said it would collapse if his goats farted at it, but it's lasted 4years. Lately  I've been copying a local design: Pairs of posts 6 inches apart perpendicular to the fence line made of Robinia pseudoacacia. Short horizontal rails between them so it looks like a little ladder in the ground.  Pine poles slotted,  in between the rungs. Want access? slide out the pine poles from a  section. If the pine poles rot they are quick and easy to replace. Looks nice and seems to be goat proof......so far

got a pic of your fence by chance? might be a good long term solution

but my goats are dwarfs so they can slip under the fence with smaller gaps than one would expect

No functioning camera at the mo but I'll see what I can do

paul wheaton wrote:
I wish to be clear:  I've allowed this thread to remain because the subject line has a question mark in it.  I fully expect the responses to the question to be a resounding "no".  If anyone feels that the answer could be "yes", then i think you are in the wrong forum.

Well... I'm going to say "no," but for an entirely different reason!

That is, dipping fence posts in used motor oil would not be effective, in my opinion.  It might make wood last longer above ground, but below ground, I don't think it will do a thing to slow the breakdown of the wood.  (Certainly the above ground part presents a problem with livestock chewing on the stuff, so again, a no-no.)

At least one municipal composting program (Austin, TX I believe.  It was in Acres USA a few years ago.) has already proved that used motor oil will break down and be rendered harmless in a sufficiently hot and biologically active compost pile.  As crazy as that sounds, I have verified this through my own experiments.  I won't use it on food, but it can't be that poisonous if earthworms, grubs, and weeds are living in it.  Makes bindweed grow like crazy, which I can't say is a good thing!  We also know that Typha can bind up DDT, and some of Paul Stamets's experiments with fungi in Superfund sites are pretty impressive as well.

Point here being, don't use toxic gick on purpose -- ever, but if one happens to buy or inherit a site with toxic gick already there, it's nice to know there are biological remedies.

So yeah.  No treating fence posts with oil. 

They have stoves that will burn used motor oil in a lot of the garages. They are also used in smokers farmers use in fields.

"landfarming" where used motor oil is plowed into a field, has been used as a means of destroying the material for a long time. Additives, synthetics etc has made this practice more problematic over time. It is probably not a good idea unless the "used oil" is tested for heavy metals and the like before using which makes it more expensive than some other options.

Hi everyone! First sorry for my english:)
I would not suggest to use motor oil. First i doubt it is soil friendly, second if the wood is not enough dry, layer of oil will stop it from drying and it will end up with a mold.

I will share some experience from eastern Europe where i come from.
A very long time ago we have used fences like this one:



For fence posts use oak-tree- it does not have to be very dry or very fine wood. Peel it(so no pests settle there), sharpen one end.
Put that end in fire for a while, so it will get a layer of charcoal- its like dead filter it wont let any fungi or bacteria through it(all the part that will go under the ground shoud be fired).
And thats it, you got a long lasting fence post!
The other horizontal and vertical part of the fence is made from peeled(not in photo above) Norway spruce(Picea abies)- yes its a lot of work to peel every branch(they sit about 5-10 cm above the ground).
I think spruce is used because it contains a lot of resin so it mades this wood weather proofer than any other wood found in this area.
They said if the wood is cut in right time (Waning Moon) fence like this lasts 20- 25 years.

Moving this ahead just because I like the fence pictured above. I have tons of low hanging cedar branches which are fairly easy to strip to make that sort of fence.

I think we've pretty much killed the idea of using motor oil. Species selection, charring and post hole drainage can all help to prolong post life. Go to the top of this page and then down one posting. That guy has a good method for any type of wood.

Apparently when motor oil flows through a hot engine for many hours it undergoes thermochemical reactions that make it significantly more toxic than "new" motor oil.  "Benzene" is a common type of cyclic or polycyclic aromatic compound (PAC), which for simplicity I'll refer to collectively as "tar".   Mobil says that used motor oil "...Contains polycyclic aromatic compounds (PAC) from combustion products of gasoline and/or thermal degradation products".  Pennzoil says "Used oils may contain harmful impurities that have accumulated during use".  

This issue is interesting because the pyrolysis and incomplete combustion of wood also undergoes thermochemical reactions that make it significantly more toxic.  Particularly wood smoke (or "tar gas") can contain benzene and polycyclic aromatic compounds.  This condensed tar is creosote.  This suggests that used motor oil and creosote are both toxic for more-or-less similar reasons.  

Wood pyrolysis initially emits simpler "primary tars", which then react with temperature and time to form "secondary and tertiary tars" (that include these cyclic and polycyclic aromatic compounds).  These are the tars that are so difficult to simply "burn off" in an ordinary wood stove.  There's a bit of a problem with simply trying to "burn them off".  Even though the formation of these tars is less favorable at higher temperatures, the rate at which the formation reaction proceeds is increased.  So when attempting to burn smoke, most of the primary tars can be burned off but this also causes the formation of secondary and tertiary tars which are much more difficult to burn off.  

I gather that these tars are condensation products, whether they are condensing into motor oil or condensing into creosote.  But in the case of "wood char" ("charcoal" or simply "char"), I'm wondering how much of the tars and polycyclic aromatic compounds are left behind in the char.  Evidently it is not enough to poison the soil, because plants can grow after a forest fire; however, in theory it's possible that some residual tar remains in the char, existing either within the highly-porous material or somehow "adsorbed" into it like in a charcoal water filter.  Char can contain oxygen and water, but it doesn't contain food or light, so ordinarily these conditions wouldn't support life.  This makes it more difficult to know intuitively whether it is toxic or not and to what extent.  I think the good news is that even if char does contain some toxic tars, these tend to be contained within the char, and are only slowly released or broken-down.  I suppose motor oil is different because any tars can leach out of it into the surrounding soil at a much higher rate.  Also most biomes are probably less well-adapted to the presence of motor oil than to wood char.  Forest fires seem more prevalent in nature than tar pits.

The char-treatment of wood for wood-preservation followed by treatment with a natural oil is also called "shou sugi ban".  It is reported to be extremely effective at resisting the fungal attack that causes wood rot.  I figure this is because: 1) char is not a food source for fungi , 2) oil repels water, displaces air, and might block some oxygen, which fungi need to thrive.  3) presumably char holds oil better than wood.  4) I would expect the oil to go rancid eventually, but if this process is slowed by the char, it might be one clue that residual tar could be preserving the oil, possibly by containing residual tars that might be somewhat toxic to microbes or other life.  It would be interesting to know how the level of tar-content in char affected the wood-preserving properties.  

Does anyone else find this funny...."post reply" when responding to this thread?

This stuff is nasty and not much better for the environment than creosote. In fact, probably worse.

I posted this as a question in the "building" forum on 3/20/18 but nobody is trying to shoot holes in it so I figured I'd put it here where it might have more visibility. What about coating ACQ or borate preserved wood posts with several coats of coal tar epoxy? The stuff is dirt cheap, is designed for some of the nastiest environments imaginable, lasts practically forever, goes on in thick coats, would protect the preservative from leaching into the environment, binds the coal tar with epoxy, flexes with changes in wood moisture content, and certainly blocks moisture and oxygen from the wood. Coat a 6X6 coming out of ground by about a foot and it should last a very long time. The stuff goes on smelly but as it cures it becomes like a hard plastic non-stinky covering. No leaching into the ground water and not a problem for animals either. Someone must have some input why this won't work.

Thoughts?

Thanks Jp.

As I understand it, coal tar epoxy is being banned in many jurisdictions for reasons of persistent toxicity. I would no sooner put that stuff on my land than I would used tires.

I like the Shou Sugi Ban preservation method, probably coupled with Dale's common sense approach to ensuring adequate drainage of postholes. Nothing else should be needed.

To stress one of Dale's points, even if the water table is within four inches of the surface at it's height, if the top three or four inches of the post hole fill is mineral, that lack of direct connection between post and the living strata of soil that would seek to decompose it will result in greater resistance to rot.

And if I was trying to fence in an area with a water table that high, even seasonally, I would think about a pollarded fence using tree species that love wet feet.

-CK

Hi CK.

The problem with coal tar epoxy, and it's attempted banning, is the carcinogenicity of the product as it's being applied. They've backed off of banning it as nobody can find anything that works even remotely similar at the price point. Once cured the coal tar epoxy becomes quite inert. I believe it is still an approved lining of steel water mains used for potable water. This is a little blurb I found on the Internet regarding coal tar epoxy:

[i]These coatings are extremely durable and impermeable to both fresh and salt water. The release of constituents from the fully cured coatings in contact with water is therefore extremely small. They are also very resistant to petrol, hydrocarbon heating oils and inorganic acids.

American Water Works Association (AWWA) standards for coating systems to be used on the interior of water transmission pipe. Currently, there are 23 approved standards under the auspices of AWWA’s Steel Pipe Committee. Of these standards, 14 deal with coatings and linings that are available for the protection of metallic pipe, and five are applicable to linings of water transmission pipe. Distinct AWWA testing standards exist for each type of lining:

C203 – Coal-Tar Enamel Lining for Steel Water Pipelines

I can't imagine the coal tar epoxy would be that harmful if they actually have standards set up for it's use on the interior of water transmission pipelines.

If you have any information to the contrary regarding cured coal tar epoxy I would greatly appreciate it.