# sealing the buried part of posts with tar?



## Tim_456

i'm building a wooden screen for some privacy around my deck. Part of this will include two 4×4 Cedar posts that will be set 3-4 feet in the ground. I've had some success by putting in the crushed limestone around posts rather than concrete. I saw a This Old House or New Yankee workshop where they dind't use concrete they used the crushed stuff.

Anyway, I just sealed my driveway with some tar-paint substance that looks fairly waterproof and I'm wondering if slathering some of that on the bottom and lower sides would a good way to seal the part of the post that's below ground.

Any thoughts on if this is worth the time and aggrevation and if it will make things better or worse in terms of rot.

Thanks,
T.


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## DanLyke

I don't know what the current thinking is, and I don't have any actual facts to bring this conversation, but…

When I was growing up out in the middle o' nowhere, the common wisdom was that you never set your fence posts in concrete because that'd form a cup that would hold water; the reason for using gravel was to let the water flow away from the bottom of your fence post.

So, in any attempt to try to keep the water away from the bottom of the post, I'd be concerned that I'd be creating a cup that would collect any water, even if it's just higher humidity flowing internally to the post itself, and keep the bottom of the post wet all the time.

However, I don't have any tests that'd tell me one way or the other, and I don't know how one would get actual facts in a process like this 'cause… well… I need to replace the fence at my house and so far as we can tell it's 50 years old. And there's lots about it that was done in ways that I think are wrong. So I don't know either.


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## jusfine

Slather away!

I have installed quite a few posts, and you will do no harm in using a water resistant finish.

I would suggest cutting the bottom of your posts so they are not a square cut, then slather them. 
Bevel all 4 sides at 45 degrees so you have a smaller flat spot on the bottom.

Old timers told me this over 25 years ago, I installed all my fence posts for our farm with tamping them and no concrete, and they are still holding up well.


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## Gregn

It was a practice before pressure treated wood to cover the in ground portion with tar to prevent rot.


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## Knothead62

This might sound goofy but my father was a farmer for many years. He swears that this is true. Never set posts in the full moon. A local guy experimented with some fence posts. The ones set in the full moon actually sank a bit in the ground. Your inquiry is a valid one and I think Gregn is right on the money. Lots of tar.


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## pawpawsteve

The primary place that posts rot is at ground level and slightly below. I know this from experience of having posts that I set anywhere from 10 to 15 years ago. Some I set in concrete and some I just tamped in. The ones set in concrete have, every one of them, broken at ground level leaving me to dig up a whole sack of concrete and post so I could put in a new post.

Now when I set posts I put a collar around the post about six inches above and six inches below grade. This can be paint or tar, I use roofing tar as it is cheap and I usually have some on hand for repair jobs. I don't try to cover the bottom of the post as (in theory anyway) this will trap moisture in the post.

I agree with using the crushed stone as fill rather than concrete as it allows drainage and it should be under the post as well so that water does not collect in the bottom of the hole and it saves a lot of tamping.

All of this is a whole lot more important if putting the posts in clay soil that doesn't drain well compared to sand where the water just runs straight through. I have the sandy soil so I mainly just tamp them in well. One of things I remember from working with Grandpa was "tamp the bottom, the top will take care of itself.

Another thing I do is put a "cap" on top of the post to keep water from entering there. These are coffee cans generally because that is what I have that won't rust. My wife hates them but if it keeps the rain out I like them. Sloping the top of the post so water cannot pool there is probably as good as covering.

Having said all of that: most of the "barn builders" around here are using a full pvc sleeve that the post sets in from the base to above the splash board. Since these are inside the building and water cannot penetrate the post of from the top, that should prevent any rot from occuring below grade. However for a fence or deck where the top of the post can get wet I don't think they would work as well.


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## CampD

Only time you use concrete to set a post is on the hinge side of a gate, helps to keep it ancorded, till it rots that is (like mentioned above). Go ahead and tar with gravel or stone at the bottom for drainage.


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## TopamaxSurvivor

WE always soaked them in penta. Some have been in the ground for 60 years, but that is an arid climate.


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## richgreer

Back on the farm we always had some barrels of used motor oil around. Before we put wooden fence posts into the ground we would take them to a barrel of oil and dip the ends in about 3 feet.

That was our standard practice as directed by my father and his father before him.

The logical question is "did it do any good?" and the honest answer is "I don't know." I can only attest that it was messy.


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## Tim_456

whoa, great advice! I'm going to cut the bottom on a bevel, slather it with tar, AND use the gravel; thanks for all the great tips! My two measly posts are going to out last everyone


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## spclPatrolGroup

If you seal the boards, how will moisture get out? The wood will asorb moisture, above the tar, and probably wick it in behind the tar, if that happens, then the tar seal would be holding moisture in the post. I would pour concrete, have it come a few inches above the ground, then once it has cured, anhcor yoru post to it, they have little brackets that you anhcor to the concrete and then your posts bolt to those.


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## swirt

I'd go without the tar. I look at it like this way. When you cut a log down and store it to later turn to lumber, you have to get the bark off, because the bark seals the moisture in and lets the bugs and other organisms get to work. 
Example: Hornbeam is a very hard wood, but if you cut a hornbeam tree down and leave the bark on, if you come back a year later, the wood will be pithy and useless.

By putting the tar on it you are essentially coating the timber with artificial bark. Tar is not the same as treating it with something that will completely penetrate and allow water to move in and out of the wood.


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## spclPatrolGroup

Also if you live within a city, I have never seen a city code that did not include a whold section dedicated to how to install support posts, so you may want to check that out if you think it effects you.


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## Abbott

I coat the part of the post that will be in the ground with old motor oil, if I don't have any around then I coat them with Thompsons Water Seal. Posts last without rot for many, many years that way. I bet tar would also work very well.


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## JoeM789

That's flawed logic. Bark isn't waterproof. And it certainly does not protect the tree from air either. Not to mention that trees do last a helluva long time with the bark on. Nevertheless. The tar has proven itself to work time and again. You cannot and should not attempt to dispute what our ancestors already learned. The problem with today's generation is that they would rather stake their claim to their own false wisdom instead of admitting that our great grandfathers knew better. I have seen more old buildings last longer than any modern ones.



> I d go without the tar. I look at it like this way. When you cut a log down and store it to later turn to lumber, you have to get the bark off, because the bark seals the moisture in and lets the bugs and other organisms get to work.
> Example: Hornbeam is a very hard wood, but if you cut a hornbeam tree down and leave the bark on, if you come back a year later, the wood will be pithy and useless.
> 
> By putting the tar on it you are essentially coating the timber with artificial bark. Tar is not the same as treating it with something that will completely penetrate and allow water to move in and out of the wood.
> 
> - swirt


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## Ghidrah

In the "old days" it was creosote, they coated everything in contact with or near the soil. All the old wooden objects, bridges railroad ties, wood house and barn foundations were also creosoted. Back in 1977 I worked for the town and we remodeled 3 of the wooden bridges in town, It's worse in the summer, everyone got burns from the off gassing from the old and new materials.

As for water pooling within the concrete, it isn't entirely true, it has more to do with perk value of the soil, the lower the value the longer water remains suspended in the upper soil column. Any rocks etc, in the soil column moves around during the winter, house foundations, (block and mono) have been tarred for decades, when the winter comes and the soil moves, (heaves) it grinds against the tarring and can and does scrape it back to bare concrete. In the early to mid 80s as the foundations were backfilled many builders stuck 3/4" rigid foam at the frost line to add protection.

Treated lumber comes in a few types, CCA, ACQ, CA, SBX and MCQ, (may be related to different parts of the country) and a few grades, marine grade, no ground contact and in ground contact lumber. All wood rots, some slower than others, cypress was great, find that today, cedar, black locust and walnut.

Throw mason sand down and pack then 3/4" aggregate, mix a 60lb bag of quikcrete then set the post in and plumb. If your soil has lots of clay lighten it up with mason sand and compost, 1/2way fill the hole, tamp and flood, let perk and when clear fill the hole. Leave the plumb sticks in place a couple 3 days then remove.


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## panamawayne

Wood railroad ties were tarred and laid on a bed of crushed stone… it makes sense to me.


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## NZSixNine

For what it is worth, I built a drain spout into the bottom of a five gallon plastic pail. Put a wire mesh screen above the spout exit hole (bending down the edges to keep it up off the pail bottom) and put old tar paper and roofing shingles in the pail and fill the whole ting with Diesel fuel. Leave it for a week or two and then it's ready to treat your wood. I've used it on my deck with good results (once the evaporation process takes car of the odor) and on posts, I set them in a pail full of the stuff for several days before setting them.

So far, so good.


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## runswithscissors

My experience has been that when a post rots off, it's always in the first six inches from the surface of the soil. In clay (wet) soil, I've always found the bottom to be sound when I pulled out the stub. I'm guessing the water kept out the oxygen. I've seen the same thing happen (but just with one post-so far) to a post set in sandy loam (i.e. well-draining soil).

I've notice that all the treated 4X4s at the BORG have a tag that says "not for ground contact." At Lowe's, on the other hand, theirs say "For ground contact." You have to look at the tag to be sure what you're getting.

I have heard that the old timers would plant black locust posts, then pull them up after 50 years and plant the other end for another 50 years. I haven't been around quite long enough to check this theory out. Anyhow, black locust is hard to find around here.


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## timbertailor

Go with gravel only. That way the post can dry out. Tar it and you are right back where you started.

I do a lot of fence work with all the hurricanes here in Houston. Gravel is the way to go. Also makes it easier to go back and straighten out a fence.


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## rosebudforglory

Hey guys, being a horse person and of some age plus remembering the wisdom of how our elders years now gone - put fence up without concrete or even gravel period. Gravel crusher run to rock dust might be used by some depending on where they lived. But the over-riding criteria was and still is the soil - if sandy, you had to use rock dust to tamp because the sand when dry would be too loose, In good draining loam soil, you could go with rock dust mixed in with soil and it worked pretty well. However, with clay or expansive type soils never would you put use larger gravel then rock dust - keeping in mind by putting gravel in the hole bottom - any depth - would allow water to seek the path of least resistence (the gravel in the hole) and it would just flow in and sit there until the soil finally dries and pulls it out. Think about it. This is how drain systems are built using gravel so the water will flow out of soil, into the gravel and then depending on situation, into a drainage pond, or drainage pipe to another area. It works the same in setting posts. Now coarser rock dust - can work the same way if the ground is clay and water logged. However, in these soils - making sure you have the right soil contact pressure treatment, and not using any gravel nor concrete is best so water isn't allowed to pool around or held against the wood for periods of time. I know right now (well 2014- now subdivision) where fence posts (cedar, oak) were installed in late 60s to very early 80s and they are still working just fine including the oak boards. We used whatever posts were least expensive at the time - oak posts and boards were green. 16'-20' posts were picked up at lumber saw mill and taken to preservative treatment company. They had big vats and they cut your posts in half (8'-10') and then chunked them in vats and we went back to get in a couple weeks - about 50-100 at a time. We took them to the farm, put them under cover stacked loosely to let them dry out pretty well (a month or more). When ready to put another section in - we pulled how many posts we needed - and put them in barrel we kept with pine tar & turpentine to thin so the bottom 2' were covered overnight or if in hurry just slathered it on with stiff brush and into the hole they went. Due to heavy clay though fairly high (not sitting in water) we only used existing soil to repack holes with maybe a small bucket of rock dust on top. The big thing that is so different from today from watching fence contractors and amateurs putting fence in is they are in such a hurry - they don't know how to properly pack and tamp and they want to be done in a hurry so the concrete is faster. But the concrete absorbs and holds moisture against the wood for ages, they put gravel at the bottom and don't properly slope top of soil/concrete so water just runs down along sides and from the soil into concrete/gravel. This along with the soft fast grown pine and safer wood treatments - means posts that last less than 8-10 years instead of 40-50 plus years. Tamping should be done in 1-2" increments, packed hard in between layers with heavy steel tamping tool (we had a old oak one fashioned round and smooth like a small diameter garden tool handle sanded so no splinters. It got a sanding off each year and wiped down with linseed - they will last for years but start off with one pretty tall as the will get worn down. In later years, trying a special made heavy steel one - it took less effort as you could let the weight do some of the work. However, proper tamping takes time though to me it is still preferable than the whole mess mixing and cleaning up from concrete. Sometimes we would partially set the posts within 6" or so and poured a small bucket of water in to settle everything and then the next day finished tamping with dirt and rock dust so we could form a nice slope st the top but sometimes we did it same day. It's so important to not have any air pockets and the hole to be tightly packed so the top doesn't collapse and water to just stand in a depression at the top. We then lightly painted the posts all the way up with thinned down pine tar/turpentine mix. It dried for a week or so - depending on our showing schedule and how fast we needed to enclose a section. We didn't buy oak boards until ready to use and depending on lumber mills hardwood/softwood schedule. Oak boards have to be drilled out (nail holes) while green - once they harden it's like nailing in concrete which is why they last so long on fence. If you have the strength you can nail green but you can split and beat up too much so easier to lift in place, mark holes with pencil, drop down drill, etc. Once you have put in 100s of posts you get pretty accurate at placement and you can cut and pre drill boards in shade of barn and then take load out to put up. You must absolutely must put boards on posts with growth rings facing posts so as they dry they pull tightly towards post and not outwards putting pressure on nails and causing a popped board for livestock to run into. I know some of you "jocks" out there think that's a bunch of BS - say you never have a problem with fences, barns, decks, etc but if you do your own and follow the project for 3-4 years or less - you know what I mean. Now that said, not every board will do it - just depends on that particular tree, it's age, moisture content, growth pattern, etc. However, to me most will do it and we learned the hard way. My grandfather, and farming uncles tried to tell us - and the couple of seconds looking at the end of the board to determine how the growth ring (half moon) is going is more than worth the time of constantly having to nail the board back down and/or replacing. People on farms don't have time to redo nor money to replace - then or today. We painted (white washed) or used the thinned out pine tar mix on the boards after they had been up for a while and dried. There are farms especially in KY, NY, Md, Va horse country that the same fences have been up for 40-60+. years. Everyone hates to have to replace because oak and cedar is more expensive and not the same density as years ago. You can't really find someone to custom treat wood these days and we are mostly stuck with big box stuff. Pine tar is more difficult, expensive to get but you can find it at tack shops but we use to get it in gallon - now I just see small little cans. I would think if you can find a lumber/saw mill close by you can purchase the wood and you want rough cut anyway not planed down which also increases cost. But remember and ask questions - raw wood just cut has to be sticked to dry. If you can buy from lumber mill that already stick dried or kiln dried if you can afford it - it's better. But if you have a shed - you can buy green and stick it the same way for a few months yourself though you will have to turn a couple times. I can hear anyone who has made it through all this saying - it's too much trouble all this. But I'd rather put up something that will last 30-40 years than every 5-6. And all fence, concrete or not requires maintence if you want it to last. In our case, as we checked lines to make sure no boards had been knocked/kicked/rubbed down or split, etc, (the painted white boards some horses would chew) - we just carried the tamper with us and gave a quick tamping - worked well after good rain. We carried some rock dust (as we have multiple quarries in area) in a bucket along with a couple boards and tools and could very shortly get around a pasture and be set for another 6 months or so. I think today we try so hard to get out work and to move quicker and quicker that we cost ourselves more in the long run. We forget those before us figured out how to get things done without today's modern equipment and chemicals and many of those are still standing. In Europe, Asia there are many buildings 600-700 years old still standing. There are stone buildings thousand yrs old - still standing. We have houses here put up 100-200 years ago with same glass windows and metal or slate roof. But for some reason - we can't build a new house today without knowing the windows will need replacing in 8-10 years, the roof 20-25 maybe, most of the appliances that use to last 20 plus yrs will be shot in 6-10. It just makes no sense to me. Each new appliance I have bought has had to be replaced faster and faster - I remember my grandparent's old washer and frig of 30 plus yrs old. My last heat pump was 25 yrs old and I'm told my new one at 4-5x the price, isn't going to last more than 10-12 Just crazy.


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## bondogaposis

The best way to do is not to bury the post at all, but use a sono tube to pour concrete in, then use a post bracket on that. Like this and this.


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## GR8HUNTER

> The best way to do is not to bury the post at all, but use a sono tube to pour concrete in, then use a post bracket on that. Like this and this.
> 
> - bondogaposis


DITTO ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ :<))


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## Redoak49

+1 on Sono tube, concrete and post bracket.


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## fivecodys

> Only time you use concrete to set a post is on the hinge side of a gate, helps to keep it ancorded, till it rots that is (like mentioned above). Go ahead and tar with gravel or stone at the bottom for drainage.
> 
> - CampD


X2


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## Gilley23

What about if you were going to mount a singular post with something extremely top heavy, like a 60lb birdhouse?


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## MrRon

> I remember my grandparent s old washer and frig of 30 plus yrs old. My last heat pump was 25 yrs old and I m told my new one at 4-5x the price, isn t going to last more than 10-12 Just crazy.
> 
> - rosebudforglory


It's called planned obsolescence. Sell more; make more money.


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## MrRon

Rosebudforglory, I'm setting some posts for a ground level deck. The soil is a fine sandy loam, soil class 2. What would be the best treatment for the posts and do I need to use concrete?


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## Gilley23

Anyone have any input on this? I was going to concrete this sucker in, but now you guys have me wondering if that's the best plan of action.



> What about if you were going to mount a singular post with something extremely top heavy, like a 60lb birdhouse?
> 
> - Gilley23


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## TopamaxSurvivor

Put 1/3 of the post into the ground. That should hold it.


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## Hermit

Paint two coats of copper green on whatever post you decide to put in the ground and forget about it. Best stuff there is in my opinion. I even use it on pressure treated posts at times.


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## Holt

Not a scientific opinion, but when I set the "pole" for my Mother's power, I used a 20' 6×6 with the bottom 6 feet "painted" with the black stuff you use on roofs to seal up vents or other breaks in the roofing. Around here we call it Bull, but that wasn't the name on the gallon can. I suspect that's the brand they used in olden times <g>. The soil is all red clay (and wasn't that a delight with the post hole diggers). To date it's solid, but that's only been three years…

I've used Copper Green on the cut ends of PT lumber and it seems to work. Again, only been a few years and that lumber isn't in contact with the ground.

For your application, have you looked at OZ-Posts? If you have a jack hammer, doesn't get much easier than those.


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## robosan

I got a first job to replace a falling fence, 4×4 posts, 2×4 horizontals and vertical planks. This was in Palm Beach County Florida. The posts were buried without concrete on a very sandy and wet soil. The water table on that land can get to be very close to the surface. Flooding in not unusual so there soare drain channels and drain ponds everywhere. The posts were three feet deep. Every post had some level of "rot erosion right at the surface of the dirt. The rest of the posts' area was sound. The posts above showed had the usual mold and some nails were rusted with rot around the nail, I.e. loose planks. Because of that, I started the three prong attack mentioned at the end.

The three feet of post all the way down to the bottom were absolutely soaked, but really only the surface showed any kind of softness. Remember all the great lumber acquired by wood turners an such from trees sunken in lakes for decades? I thought of that and came to the idea that the are that rots seems to be the area that is both wet and exposed to the air. Something must grow there that rots the wood.

So after that, I started just protecting the area around the surface with maybe ten inches of concrete, not too wide, and tapering the top away from the post, just abobe the dirt to shed water. On very sandy soil prone to hurricane winds, those extra inches of diameter are essential to keep the fence to begin to tilt. 120 mile gusts can push the fence sideway, if not break them. Twelve years later, those posts look fine.

Another fence, I used a three prong attack. (actually four. I cut the top end of posts slanted too.) Roof tar in the ground end, a tapered ring of cement on the surface and just below and a stain throughout the fence. 400 feet of fancy horse type fence with translucent stain did cost a bit, about 15 gallons with a hand pump sprayer. But the fence will last much longer in those humid conditions. Looking good after five years.


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## therealSteveN

I wouldn't slather, at least not the bottom of the post, for fear it would allow water to go down the pourous post, and become locked in by the tar, at which point you are doing worse than the concrete would have by sealing the moisture in. Use your pack just like you planned, and put the tar on as a second coat on the drive.


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## runswithscissors

Whenever I've had (untreated) posts rot off, the damage was in the top 6 or 8 inches. Below that, where the damp clay sealed out the oxygen, the wood was always sound.

If you are using treated posts from the big box store, be sure to check the tag stapled onto the end. It should say "for ground contact," in which case it's good, but it it says "not for ground contact," heed that advice. Pressure treated wood all looks the same, and it's easy to be fooled. Don't ask me how I know.


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## metolius

A few years ago I set a few pressure treated posts in for hinged gates. I won't dally in the debate about concrete, gravel, and coatings but I will say, "I set 4 posts perfectly vertical and aligned, and 3 posts remain perfectly vertical and aligned today".

The 4th post twisted and bowed. It held a latch, so at least the gate's still swinging. The first year, I trimmed off the bow+twist and flipped the waste and glued it to the other side. After painting, it actually looked like a straight post again .. for a month or so. I've had to move the latch 3 times now as that post won't stop moving. It is bent over like a wind whipped spruce on the north coast. The concrete is real quick at de-motivating my gumption to work on it.

- If I had let the posts sit out for a few weeks before putting them in I would have identified the problem piece. 
- If I hadn't set it in concrete, maybe I would have replaced it already.


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## AlaskaGuy

The old timers way

At the 10:18 mark he says don't put any tar on the bottom of the post.


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## newwoodbutcher

Tar on the bottom will encourage rot by holding in the water.


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## ArmyOfNobunaga

I'm the manager of a reclaimed wood company. I see 150 year old posts treated like this and they are still sound enough for me to sell them at 15 dollars a bf. I don't think you are going to go wrong like this.


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