Black Locust Timbers For Fence and Gate Posts

A long discussion of Black Locust as a utility wood. October 1, 2009

I am planning on installing a gate in my driveway and using 8x8 black locust timbers as posts to hang doors on. The timbers would probably be cut only a month or so before I started working on them. I plan on planing and squaring the surfaces, letting them rest for a couple of weeks or so, and then turning them into octagon posts. Of the 11' or so lengths, the bottom 3' would be buried underground in concrete. My concern is that once the hinges for the doors are placed and the doors hung, the timbers may move, twist and bow as they continue to dry and screw up the way the doors are hanging. Is there something I can do (other than wait for the timbers to dry, which is not an option) to minimize this possibility?

Forum Responses
(Sawing and Drying Forum)
From contributor G:
Would you consider an 11' piece of 4-6" pipe with an eight foot octagon shaped sleeve slipped over it? I believe that locust moves a lot in drying and if one side is exposed to direct sunlight all year round, I would expect anything to move enough to interfere with the hanging of a largish gate. I suppose that you could hinge the gate panel to a 2x6 or such and arrange a system of lag bolts in elongated holes that would allow you to make adjustments by tightening and loosening the bolts, putting wedges in as required and in general realigning the hinge board to the post from time to time.

From contributor T:
I have done similar orders for people doing projects just like this in the past. Black locust can warp if not sawn from a stable log, and in your case from a core cut beam. If your beams are core cut (with the center of the tree in the center of the beam, throughout the beam's length) then they will remain very stable as they dry. Shrinkage will be minimal and will not affect your gate's alignment.

The larger issue here is how long is the gate itself, and how far out does it protrude from the locust beam? Large gate setups very commonly use an extra long beam for a post, and are cabled from the tip of the gate to the tip of the post with some sort of tensioner to pick up the gate as it wears down over time. This depends on how much the appearance matters, and if it is a fancy, ornate gate. You also can add multiple hinges to make the gate stronger.

From contributor E:
Good suggestions! I would be apprehensive about hanging any weight on a green post. That said, most hinges have threads that allow for some adjustment over time. But the movement in the post may be so much that, while you can adjust it out to keep the gates in line with each other, the posts may be leaning in toward each other so much that it doesn't look right. You could also have them lean towards the road or house (one in one direction and one in the other direction) such that the whole assembly looks out of sorts. Best to let them dry for a season before loading them too heavily. Is that possible? Could you buy some that have been drying for a while? How about some temporary center supports to hold the ends of the gates up?

Someone here suggested to alligator char the part of the locust post from ground level and below to promote longevity. I liked that suggestion. I've seen green black locust sprout branches and grow when put into the ground with bark on them after being freshly cut. They rotted prematurely. Seasoning for one year would have made a lot of difference. Alligator charring them would have made up the rest.

From contributor J:
Any wood set in concrete will rot. I would see if there was a better, longer lasting approach to this design.

From contributor C:
Since creosote is not readily available anymore, we use blue stone in a barrel. Just soak the wood in it until you see the color climb up the post, then let dry. Blue stone is also approved in Canada for use on organic certified farms.

From Professor Gene Wengert, forum technical advisor:
Locust is quite impermeable to liquids. In fact, that is why it pops so much when it is burned... the water inside is converted to steam but cannot easily escape. So, this is one species that soaking will not work well with. Of course, the soaking idea has been around for a long time using various chemicals including some very strong ones. Tests by the US Forest Service continue to show that soaking is not very effective even when the species is more permeable than locust. Part of the reason is that we need 100% effectiveness, especially in a gate, or for a fence that houses expensive animals, where a failure is very expensive. Contributor J said it rather well.

Bluestone is copper sulfate and it will leach out and reduce its effectiveness with rain and water exposure. One might also question whether we want to contaminate the soil or ground water with copper as the chemical leaches out. Copper preservatives have been banned in Europe.

If you use a fairly green post, it will shrink more than 1/4" as it dries and that will let dirt and water into the hole and result in ideal rotting conditions, even for locust with its natural resistance. Contributor G's idea of using a metal post is one very effective way to avoid problems and yet make the post look like it is perfect. (The hole in the post also lets the wood dry without as much cracking.)

Be aware that fasteners installed in green wood will, when the wood dries, lose a great deal of strength. It would be better to use bolts (rather than lag bolts) that have a nut on the end so you can tighten them as the wood dries. It is also required to use special fasteners if you do use a copper-based preservative to avoid metallic corrosion due to dissimilar metals. These would be the same ones used for CCA, ACQ, etc.

Do you care about how the top of the post looks? If so, you might consider a water repellent on the top to avoid cracking, etc. Oftentimes, critical fence posts will use a cap... It works well but does not look pretty.

From the original questioner:
Thanks for the suggestions, everybody. While I would really like to wait for the posts to dry a bit, this project is part of an escalating war to keep deer out of our garden, and I would like to have a fence and gate up by late spring, at the latest.

Using a "hinge board" is an interesting idea - I would probably use two hinge plates on each post with four bolts in each so each plate corner could be adjusted horizontally and vertically. Unfortunately, I think the ugly factor would rule this out for now.

Is blue stone preservative available as a ready made product? Anybody know of any sources?

From Professor Gene Wengert, forum technical advisor:
Regarding the effectiveness and dangers (it is a human poison, for one) of copper sulfate preservatives, see "Handbook of Preservatives", page 345.

From the original questioner:
Thanks, Gene. I missed your first post - I think I posted at the same time. I will skip any sort of preservative, but was planning on using repellant on the top of the post. Was also considering capping the post, with copper if I could figure out how to do that, or with a piece of locust to at least cover the end grain on the post.

Thanks for your suggestion to use bolts to secure the hinges. I probably would not have thought of that.

I am not overly concerned about shrinkage - I am more concerned about the timbers bowing or twisting or something of the sort, although contributor T's comments have reassured me a bit in that regard.

I am actually thinking of not setting the posts directly in concrete, but leaving a small gap all around the post and filling it with fine gravel or stone dust, which I am hoping might settle down (by itself or with a little help from me) as the post shrinks, fill in the resultant gaps, and keep it plumb.

Also figure that I will need a layer of gravel beneath the concrete. I have an excellent mason who has done this kind of thing before and who I am fairly well convinced will know how to guide any water that does seep down the side of the post away from the base of the post.

From contributor N:
Wars fought against whitetails are properly fought with high velocity lead.

From contributor R:

A good gate post is ERC sawn at about 8" x 8" and as long as you need. Very little shrinkage and no twisting and can be used green. I use pea gravel rather than concrete. The pea gravel will let water drain away. The post will set tighter and tighter as time goes by. The post should be good for 60 or more years. Corner posts where I grew up in central Indiana are still good after 80 years. Weathered, but sound.

To keep the post straight, bracing is much more important than what you pack around the hole. A post is set about 8' from the gate post, then a diagonal post from the top of the second post to near the base of the gate post, then 2 strands of # nine wire from the base of the second post to 4' up on gate post. Use a stick to twist the # nine wire to make it very tight. This should keep the gate post straight.

From the original questioner:
Thanks. Unfortunately, the use of high velocity lead is illegal in my county.

Also unfortunately, I am not aware of any sources for Eastern red cedar anywhere near me (I'm in NY, about 30 miles northwest of NYC). The closest source I found for timbers was in VA, almost 8 hours away. It looks like I will be sticking with black locust.

I didn't consider using only pea gravel to set the post. I don't think I would be able, even with a whole lot of help, to keep each post plumb and facing the right direction, and pour gravel at the same time. (I expect that each post will weigh approximately 300 pounds.) However, as of now I intend to dump a bunch of gravel on the bottom of the hole, and then pour concrete, leaving an oversized pocket for the post. Once it sets, put the post in, shim as necessary and pour gravel around the post to keep it where it belongs. My guess is that this will have the same result, no?

I need to give the method of bracing, if any, some more thought. Six electrified wires will be screwed into the side of each post, not leaving a lot of room for anything else. I am hoping that because the locust is pretty stiff and strong and heavy, they will be able to support the rather large (5'x7') but relatively lightweight doors (190 lbs. each) without additional bracing. I may go on that assumption and figure out a permanent solution if and when the doors start sagging.

From contributor C:
Drainage is one of the major concerns. The post can be moist, but not sopping wet. Cement holds the moisture in.

Bracing for a gate that heavy (yes, 190 lbs is still heavy) can be very important. Put one end of a gate on a block of wood, then pull on the top of the same side to lift the opposite side off the ground. It takes a lot of force to hold it up.

Either you need to put your posts about 8' in the ground, you need adequate bracing, or you need to put a weight supporting wheel on the swinging side.

From the original questioner:
Thanks, folks, for being patient with me - as is obvious, I've never done this sort of thing before. I will definitely come up with some sort of bracing. This gate is not going to be strictly utilitarian, so appearance is important.

As far as using concrete goes, I was thinking that as long as there were two or three inches of gravel separating all sides of the post from the concrete, and gravel underneath the concrete and post, drainage shouldn't be an issue. Is this a reasonable bet, or if not, why not?

From contributor V:
My grandfather used a lot of black locust for fence posts in his day, and many around a concrete cow yard, so I have some experience in this area. If you leave the pith in the center, or for that matter anywhere in the post, it will rot out first, and become a highway for termite entry, causing the eventual failure of the post. This may take anywhere from 12 to 60 years, depending on the wetness of the soil below. Still beats pressure treated pine (028 retention) which for the most part is gone in around 12 years max, here in MD. You are on the right track, as far as species selection goes.

Here is what I would do were I to use it for gate posts. Get a big straight log milled into posts (big ones are rare around here). Use only seasoned posts that have no pith anywhere in them, and after cutting your octagon shape, cut a notch about a foot from the lower end, kinda like a groove in a piston, but wide, and c shaped. This notch will keep the post from lifting out of the concrete. You might also want to wrap the bottom of the post with heat shrink plastic like they use on boats, after you cut the notch. You can put it in concrete, or tamp it in real good with sand and stone dust. If I was doing it, I would brace it to ground opposite the way the gate will hang closed. You can do this with a cinder block with a cable through a hole, and a turnbuckle for adjustment. Just bury the block in a hole about a foot and a half deep.

Now a few words about deer: Make your gates tall, with no cross boards on the side the deer are coming from. (Deer have limited eye movement vertically; they have to lift their head to look up.) If they see a line across their field of view, they will try to jump it - it does not matter how high. We have had good success with an electric fence about 24-36" high, single wire around the edge of our garden, a post at each corner and handheld spring loaded gate latches that disconnect easily to allow tilling. Trick is to use tinfoil strips coated with peanut butter, put up early in the spring, to coax the buggers to taste voltage and learn to respect the fence!

From contributor E:
If you know someone with a Shaver post driver you can forget the concrete all together, although I'm not sure if one is available that will drive a post that long.