I am building a fence and I am not sure which method is the reccomended way to set the posts. The posts are 4 by 4 pressure treated and will be approximately 6 feet above ground with 2 by 4 rails (cross members, 3 of them). The face boards will be a full 1 by 6 alternating them with 1 by 4’s. Approximate space between the boards are 1/2″.
Amount of work is not of concern but the best end product is of most concern to me. The holes are being dug with an hydraulic 12″ auger to a depth of 36″ since our frost goes to about 36″ in central New York. The holes for the posts can be filled with compacted removed material, crushed stone or cement/concrete. The cement can be premixed or water added to the hole with each bad as the cement is poured into the hole. I was also told of using sand rather than the crushed stone so that full compaction is obtained. My former employer had specifications when putting posts in the ground to wrap the posts with tar paper for the depth of the concrete.
Would like to hear some views from anyone. There was an article in one of the monthly publications of Fine Homebuilding about construction methods for a fence. However, I can not find my issue. It was woithin the last 2 years that the article appeared.
Thank anyone for your time and thoughts.
Replies
In general, for normal soil types, the best choice for wood posts is a backfill of fairly fine crushed rock, well-tamped. Put a little in the bottom before setting the post as well.
In exceedingly sandy or marshy soil concrete may work out better, as it may for metal posts (since it increases the apparent post diameter). But concrete increases rot and increases "frost pull" on wood posts in most normal soils, plus it tends to work loose, while the crushed rock will stay tight.
Defionitely do not use crete. It will hold water to the post and make it go punky faster. It will also provide a rough toothed edge to the set for the frost to grab it and lift the post out.
That was the reason for the tarpaoper wrap. You can use plastic too. it provides a slip sheet for soil to be able to slide up and dowmn with frost and not freeze tight to the post to get a lifting grip. This especially in the top two feet or so of the hole.
For backfill - grasvelly is best so it deosn't hold water but if it has a little clay fines it will pack tighter and stay put better. Topsoil would be worst
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I agree with what the others have said so far about setting posts. A couple things about putting up the fence itself that may help you if you are somewhat new at it--one I "discovered" and one I was told: Set the posts one at a time and make a frame the size of the infill between posts (make sure the frame is square and has corners braced). Then you set first post, making it plumb both ways, then clamp the frame to it and mark where to dig the next hole. You can even clamp the frame to both posts to help square/plumb the second one. The frame also helps you find a level line between posts if the land rises and falls. (You'll still, of course, have to have a long line pulled tight between corners of the fence to set the posts to so the fence runs straight.)
A common way is poured concrete.
Down side is that that the posts will rot quickly. The concrete will shift and the purchase, mixing and placement of the concrete is labor intensive and not inexpensive for little return.
After talking to old timers I use their method with a slight twist:
Pack the posts in crushed gravel. A packing rod is best but a shovel handle will work almost as well and is a whole lot lighter. Don't use river rock of any smooth stone. You want the edges and flats to key together and lock when packed. Don't go too fine on the gravel either as you want the fill to drain. A mix of sizes is good.
Place a couple of inches of gravel under the posts to keep the vulnerable end grain as dry as possible. Be sure to go below the frost depth to limit frost heave even though the well drained gravel should limit heaving if you are just a little above the frost line.
The gravel draining well and drying quickly will limit rot in the critical zone 6" above and below the ground level. Where most posts fail by rotting out.
For added protection, the added twist I learned from a local farmer, is to use a thick coat of roofing tar thinned with mineral spirits or turpentine so it soaks in some and coats the post for a short distance above and below the ground level.
To limit the mess this is best done a day or two before you set the posts to allow it to set up so it doesn't get smeared around during handling. If it is just a little soft a little sand, dust or dirt sprinkled on it will help keep it off your hands and tools. Keep a little thinner and some rags around to clean up any spot before they spread and migrate to the carpets.
If you put the tar on shortly before setting the post make sure you get a good coat on and wrap the section in a couple of layers of newspaper taped on. This can remain in place and will fall apart after a few rains. Any shreds sticking that bother you out can be removed once the post is set.
Set this way I have seen even untreated posts last decades in good conditions. Set in concrete I have seen even pressure treated posts rot out at ground level in a couple of years.
I have made it a habit to use a frame to maintain the spacing while setting the posts but what I've had no problems with for posts set as long ago as 30 years ago is to use a few inches of loose stone at the bottom and I always set the posts, especially the gate supporting posts, with dry concrete.
It may take a while to set as solid but I don't care as long as it doesn't shrink and give the gate any wiggle at all. Wet concrete always shrinks as it drys leaving a small 1/8" gap that collects water below grade. The gate can be hung and used within hours. I imagine stone dust would work as well but is harder to come by.
Might not be an option -- but if you really want it done right have them driven in -- no packing and they are tight and rigth to the line (only down side is if you hit a big stone). If you can't have them driven, go with a smaller auger, less to mess with. I have maintained 2 miles of fences since 1968, some are still in the gorund and holdoing on -- I really like the round posts that are 6" in diameter -- they look great and are a substantial post -- can get in 7 or 8 ft length