CONCRETE FENCE POST FORMS - Making Posts

THIS TWO-FORM GATE POST SET IS REALLY THE SECOND USE OF
THESE TWO FORMS.  I BUILT A SIMPLE SPREADER BAR TO USE FOR
LIFTING THE PAIR

          I selected a place with easy access for the first try at pouring fence posts in place.  We are building a fence so we can better control access to a creek bottom that runs through part of our property.  There will be several access points along the fence.  The site chosen meets the criteria of being easy to get to.  It is also in the open and immediately adjacent to a roadway, fairly flat, and has no sticky clay in case it rains while we are experimenting with the post forms.

THIS PHOTO IS OBVIOUSLY SIDEWAYS.
IT SHOWS THE BASE RING FORM AND
THE RE-BAR ASSEMBLY TO STRENGTHEN
THE TRANSITION BETWEEN THE BASE
AND THE POST.

          Long ago, when I was young and strong, I didn't think twice about digging a hole just the right size with a shovel.  Now, I am either lazier or smarter.  We use the backhoe to dig holes for anything that involves two or more posts tied together.  These post forms are designed to be poured in conjunction with a 24" x 6" base ring.  The bottom of the base ring is set at 30".  We have no deep frost line to worry about.  We do have high shrink/swell clay (obviously not at this site) but the concrete posts with bases like this haven't so far been affected by that problem.

          I set up the laser level to get the bottoms as close to even as I can.  They are dug about three inches deeper than needed and then backfilled and compacted as much as possible to form a hard footing for the base.  The re-bar is a new addition.  Previously there didn't seem to be a need for re-bar since the entire outside of the post was steel.

(NOTE: This Blogspot system has a mind of its own when it comes to photos.  I didn't intend for the photo to be sideways.)

          As the post forms are lowered, we have the re-bar set loosely inside the base ring and we simply lower the form over the re-bar.

THE FIRST USE OF THE POST FORMS.  NEARLY LEVEL
AND ALMOST PLUMB.  YOU CAN SEE THE IDENTIFYING
NUMBERS ON THESE TWO FORMS

          It takes about 6.5, 80lb. sacks of pre-mix concrete to fill each base and post assembly, or about 13 sacks for this post pair.  I calculate an 80 lb. sack of pre-mix will yield 0.6 cubic feet of concrete.  The simple calculation is, total cubic feet divided by 0.6 = the number of sacks of concrete needed.  This number will depend upon how you mix the concrete and how you get it free of voids.  I mix one sack at a time in my little mixer (you can see it behind the top rail in the photo) with as little water as it takes to make it not granular.  We don't have a vibrator so we do much taptaptapping.  For these posts the concrete needs to flow more than if you are doing flat work but only enough to get the voids filled.  We also add a half-pint of dry cement to each sack of pre-mix.  It takes about 45, 80 lb. sacks to equal one cubic yard of concrete.  A half pint of cement weighs just less than two pounds so the mix is increased by about one sack per yard.  If you mix the concrete wetter and you don't do much tapping, a sack will probably go a little farther but you will have an inferior product in the end.

FORMS FILLED AND EXPOSED CONCRETE COVERED.

          It doesn't take long to mix up and dump and tap 13 sacks of pre-mix concrete.  You might notice here that I used four sets of vice grips to set the spacing on this two post set.  The rails go completely through the post and extend about an inch on the off side.  The vice grips simply clamp the rail to the socket.  Surprisingly, setting the rails to extend to the height of the flanges at each end with clamps on the ends of the top and bottom rails made the unit almost square and plumb.

         
There are two more things to point out in this photo of the filled forms.  First, the 2x4xVicegrip system to plumb and hold the unit is no good.  It takes forever to set the unit in place on the fence line and parallel and level and plumb when you have to adjust this stuff every time you move the forms a half inch.  The blocks to support the height and level of the unit work okay because absolute height and level accuracy are not necessary and you can slide the whole thing or each end on the blocks.  The next shop project is to build some simple screw adjusters to take the place of the 2x4xVicegrip setup so the plumb can be dialed in without any effort.  Secondly, these forms are heavy enough that the bottom rail is bowed up by their weight hanging on the rail's ends.  I have some heavy 2x4" channel iron that I am going to set under the rail, with the flat side down, to support the rail better but still allowing the unit to be moved.  The other idea is to make a tripod like setup with universal adjusters to attach to the top and bottom rail of each end of the unit or three to use for a three post corner or T.  With such a setup, the chore would be to get the unit set up with the tripods.  The adjusting would be easy.

REMOVING THE SECOND FORM

I had no good idea how long to leave the forms in place.  The local concrete merchant thought two days would be sufficient.  I gave this first set four days.  A small impact wrench makes quick work of removing the bolts.  The warp in the forms also became our friend.  Even with form release of some kind (diesel in our operation) these forms are intricate enough to want to stay where they are.  The warp helped get them started away from the green concrete.

GREEN BASE AND POST BOTTOM

          The base forms are easy to remove unless you forget to clean up around them when you finish pouring.  I use a little release on the bolts and I use some on the outside of these forms also. I would use form release on the outside of the post forms too but it would end up in the mix when you scrape concrete from the ring stiffener

TWO FORMS READY TO BE CLEANED

          It takes only a few minutes to wire wheel the excess stuff from the forms.  A coat of form release applied when you clean the forms and before you bolt them back together will save the time and effort of trying to coat them when they are together or of having to take them back apart to coat them.

TRAGIC ENDING TO OUR FIRST ATTEMPT AT CONCRETE POSTS

          Sometime on the fifth day, after the forms were removed and before the concrete had a chance to cure much, this first set apparently got bumped hard enough to crack the posts right at the bottom rail.  The set was still standing when I noticed the crack line.  I pushed the set over and broke it apart before it had a chance to cure farther and make it harder to salvage the rails.

          Of course, those of you who know me will know that I am now worried that the volume of concrete between the rails and the form wall isn't enough to form a strong post at those points.  The second set is now about two weeks old and it seems to be very strong.  I haven't asked it to hold tension or hold a gate yet but that is the next test.  We'll see.

GREEN SECOND SET JUST OUT OF THE FORMS
I LEFT THE FORMS ON THIS SET FOR SIX DAYS

THERE WILL BE A 16' GATE BETWEEN THESE TWO SETS

 

THE SUPERVISOR AND HIS ASSISTANT

          These forms have been a fun project.  The posts will be fairly expensive but they should outlast me and if the cost of alternative materials continues to rise they may become very competitive.  The cost of these posts compared to other options is not exactly straight forward.  If you constructed a two post set like these and used the same materials except used concrete for the posts, the concrete costs about $18.40 per post and base.  A number 1 tie is over $25.00 in this area and a 6"x6"x8' treated post is about $16.00.  If you used wood posts you likely wouldn't use the tubing rails, or any rails.  Hem/Fir 2"x6"x8' cost about as much as I paid for the 2 1/2" tubing, but I bought a truck load and got a good price.  If the posts turn out to be strong enough, I plan to make some more traditional braces with an X or a traditional H between the posts which will save three or four rails.  I'll let you know.

JCE
         

CONCRETE FENCE POST FORMS - Construction

Corner and Gate Post Assembly using 8" Irrigation
Mainline and 2.5" round tubing

Latch Post Assembly and single posts with flanges to
hang 2X6 panels.  All are Concrete filled.

          About six years ago we dug up about 600' of old 8" steel irrigation mainline.  Over time, it had rusted to the point of being unusable.  As really good fence posts became harder to get and the price of even lower quality posts continued to rise, I decided to use the old mainline for corners, gate posts, intermediate braces, and other places where we needed strength and permanence.  I built the assemblies at the shop and we hauled them out, dug holes, set them in, and (since the irrigation tubing is thin walled and not able to serve as a post by itself) filled the whole setup with concrete.  

          Six hundred feet of tubing doesn't go as far as you might think.  We made corners and braces and fancy setups with wood panels between and we made water gap braces.

           Finally, we ran out of the mainline.  I priced thin walled tubing and I looked at the secondary steel yard in our area.  The best price I could get on new tubing would have made a seven foot post blank cost about $45.00.  The secondary yard didn't have much quantity but the price of secondary steel has gone up so much that each post blank would have cost about $30.00.

          Concrete fence posts are not a new idea.  Many areas around the U.S. and elsewhere have used concrete posts in areas where wood is not available or where wood will rot out about as fast as you put it in the ground.  Most concrete posts, however, are manufactured in forms lying horizontally, cured, and then installed about like a really heavy wood post.  The idea I had is to take the forms to where the posts are needed and pour them in place.  I decided to build three forms.  Two identical line forms and one corner form.  The corner form later morphed into a three way form.   

Tube with cutouts for sockets

   

The Raw Materials:  8" x 82" x 1/4" steel
tubing, 3" id steel tubing, 1/4" and 3/8"
steel plate, and 5/16" x 1" flat steel 

I found enough materials at our local secondary steel yard to do the job.  They cut the 8" material to length for me so I wouldn't have to go home and get my trailer.  Everything is secondary except the 5/16 by 1" flat strip. The cost was $468.00. 

           The fabrication is straight forward.  I used 3" id  x 1/8" tubing for the sockets because I have a truck load of 21/2" tubing to use as rails.  The Stiffener Rings are 3/8" plate on the tops and bottoms, and 1/4" plate for the intermediates.  The gussets match the rings with four each on the tops and bottoms and eight each on the intermediates.  The flanges are from 5/16" x 1" flat steel.  They were simply custom cut in pairs for each location and drilled to accept a 3/8" bolt.  Each pair has at least one bolt hole to hold the pair together as it was welded in place.

Ring Stiffener Blanks

Ring Stiffener and Gussets

I

In an attempt to get the sockets more or less parallel between the line posts and the corner post, I set up the tubes with the socket holes cut out and the socket blanks roughly in place.  Two of the intermediate ring stiffeners were also put in place on each post between the appropriate sockets since they can't be easily added after the sockets are welded in place.  After worrying and fretting long enough to have done the job, I

Three Post Setup to get sockets placed correctly

Sockets

Gusset layout from drop  

Adding Ring Stiffeners and Gussets

finally decided that perfection isn't necessary here.    The results aren't elegant but there is enough room between the 3" socket and the 2 1/2" rail to compensate for some small misalignment problems.

Flanges

I also spent time making certain everything was plumb and level before tacking the sockets in place.  That was probably mostly wasted time.  Certainly, you don't want to just throw things together, but obsessing over a tube being a quarter inch out of plumb isn't necessary here.

Sockets tacked in place and Stiffeners loosely set

                                                                                     After the sockets are tacked in place, I laid each unit on a work table and tacked on the Ring Stiffeners and the Gussets.  From the start, I knew there would be some warp in the finished form pieces but I still tried to weld everything up in stages so the warp wouldn't be excessive.  When I finished this phase, the ring stiffeners, gussets and sockets were welded solid except near where the parting cut and flanges would go.

Plasma-cut line (This process was later changed to cut
only between each set of stiffeners at one time.)

The first form cracked open.  We wanted a little warp

 On the first form, I used the plasma cutter to make the cut line through the tubing, the rings, and the sockets as I went along.  After the first half of the first form it seemed easier and more accurate to snap a line, corresponding to the line through the sockets, across the stiffeners (since they stick up higher than everything else) and then cut them down to the tubing with a zip wheel.  I used those cuts to hold the snap line while I marked the sockets and I also cut them down to the tubing with the zip wheel.  Then it was easy to plasma cut the tubing between the various places and to finish the cuts through the tubing below the rings and sockets.  (The socket blanks stick through the tubing on the inside as much as half an inch and the plasma cutter can be used inside the socket itself to cut the line.)

          I custom cut all of the flange pairs before I started each cut along the length of the tubing.  With the flange pairs cut and drilled and bolted together it was just busy work to plasma cut the cut line, clean up the little bit of slag and weld the flanges in place.  The flanges are not welded solid on the outside because I thought the possibility of too much warp wasn't worth the small benefit.





When I finally cracked open the first form and it fell apart easily, I tried to forget about those times when I have welded things together that were supposed to be apart.  It's worth mentioning though, that if you don't get a clean cut line you may have an interesting time getting the parts apart.  It's also worth noting that you need to look closely to be certain you have removed all of the bolts before you try to crack the form open.

Finished inside on left, raw inside on right

       
Once the form is open, it takes awhile to clean up and weld up the inside and then grind everything smooth.  I did weld solid the flange on the inside.  After both parts are finished, I gave the entire inside a thorough going over with a stiff wire wheel and then coated the interior with form release, diesel in our case.






                                                                                      The corner post began as simply a corner post

The Corner Post has three columns of Sockets so it
can be used as a corner, a T, or a three-in-a-line brace.

with sockets 90 degrees apart.  When I finally realized that the form would still have to be three pieces I decided to add another set of sockets and make two quarters and one half piece.  The versatility is greatly increased and the labor was minimal.

Two nearly finished forms

The Corner Post has one half-Section and two Quarter-Sections

We wanted some warp but maybe not quite this much

 The warp problem reared its head, or maybe its curve, on the quarter sections of the corner post.  It takes a 3" bolt to get the parts started together.  With the large number of bolts available, though, the whole thing goes back together easily.

Even with the excess warp, the quarter-sections are
easy to put together with all of the available bolts.  If you
expand this photo you can see the index notches
between the sockets on the right.  The not visible side
flange has a single notch index in the same location.

          These forms are heavy.  The line forms weigh about 170 lb. and the corner form weighs about 185 lb.  Also, with each of these forms being custom made, I welded a "1" on the two pieces of a line post form and a "2" on the two pieces of the second line post form.  The corner post form got a "3" on each of its pieces plus it got index marks (notches with the zip wheel) so the two quarter sections can be indexed to the proper position

                                                        


                     


JCE