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Discussion Starter · #1 ·
Hi All,

Looking for insights/caution/best-ideas on this plan:

So I have about 1800 feet of 6' concrete wall I want to put around my property. Privacy, Protection from Coyotes for the small dogs, Jackass Drifter Drivers who like to crash into fences and drive off, muffler noise deflection & many other reasons.

Thought of super blocks (4x2x2) blocks, but they take a long time to cast, let dry, set into place. Plus the molds are pricey.

Figured if I could make something I could cast in place, and moveable the county can't tax me on it either. Like setting huge boulders around the property.

Decided on a self-standing concrete mold. 2' deep x 4' wide at the bottom, tapered to the top about 6-12" deep x 4' wide. This would be about a yard of concrete, 4000 lbs. I could pick it up with my skid steer and move it if need be to show the county it's just a big boulder. Plus, one-shot pours like this are easier because I can peel back my fence 4' at a time and one pour without leaving a gap in the fence for too long only to have an open range critter waltz in and kick the side of my truck.

I would set this on either compacted AZ-rock infested ground or do a Frank Lloyd Wright compacted gravel trench/rubble trench maybe 3-6" deep to prevent washout. In AZ we don't have ground heave due to freezing temps.

The idea with the wedge shaped mould would be I would use 1/4" plate steel welded and just drop the mud in from the top. Let it cure for a day and then when the concrete shrinks back, pick up the mold with the skid steer with chains or a set of lift bars welded to the mold and move it down the line for a re-cast somewhere else. Maybe spray a mixture of diesel and used motor oil on the inside of the mould to stop the concrete from bonding to the steel. I was hoping I could use the mold 2x a day, but that might be ambitious and create a mess.

Was going to get a bucket mixer for the skid steer or a 3 yard batch mixer to mix up consistent batches and dump with the skid steer into the top of the mould. Thought about getting a 12v dump truck vibrator and clamping it to the side of the mold and briefly run it to drive out any air pockets for a nicer finish rather than looking like cottage cheese.

To save on cement costs, was going to use a M5 or M7.5 mix for 1000 psi concrete since the wall really won't be supporting anything, it's more of a barrier. The aggregate I have is fractured rock, 2"x1"x1" dimensional.

Didn't want to use rebar because of the time to tie it. Thought I could hang some 6x6 woven field fence in the middle of the moulds to give it rigidity and not drive up the cost too much.

On downward sloping land sides I was going to put a 4" pipe in the middle of the bottom mould, maybe held in place with some stones while I poured the mud so that I wouldn't create a runoff water dam on the neighbors side. There are going to be 1" gaps between each pylon anyhow, but those could get jammed up with debris over time. Figured I would need some pipes ever 3 molds , 12 feet to let water pass. This also means rabbits and snakes will be able to pass. Didn't really want rattlesnakes coming through if I could avoid it. Might have to make some sort of pop-out screen cap to keep them from moving through.

I would like to reduce the cost of the moulds. If I make them out of 1/4" plate, the cost will be north of $1000 a mould. If I made 10, I would have 10k invested in moulds alone and I would need each one to last 45 pours. Is there a cheaper way with plywood or other materials that I should look at? I don't want to spend all day setting up and tearing down moulds.

Let me know if you have any ideas on what could go wrong, or what would be an improvement to doing things this way.


Much Appreciated!
 

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retired framer
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Correct, something like this just much taller: https://www.ebay.com/c/1939330623
Simple moulds are key. Figure I could always texture roll it later with some sort of pattern and then stain it. Would be probably far cheaper than trying to color the concrete mix as concrete power seems pricey for the 450 yards of concrete I will be mixing up.
We most all the time used rental forms that that were made out of form ply
( good grade of plywood with paper faced) Some outfits just left them dry and others would spay them with veg. oil. Before that it was diesel but that was outlawed
Even steel would need some extra support around it so you may not be able to cast in place.
I would think you could build the with plywood with angle iron bans bolted at the corners so if one got stuck you could just loosen the bolts.

You might rig a hydraulic jack hammer to the tractor to vibrate it.

You might save on the concrete and put a wedge of Styrofoam in the middle.
 

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Discussion Starter · #5 ·
Thanks for the reply. How thick was that plywood on those rental forms? What's paper-faced plywood: Something like : https://www.homedepot.com/p/Edgemat...ERCH=REC-_-pipsem-_-206942945-_-206942959-_-N
or
https://www.homedepot.com/p/Veranda...ctual-750-in-x-49-in-x-97-in-461877/100070209

I don't think a styrofoam wedge is going to survive a long drop of wet concrete could be a 2-4 ft drop as I fill the top of the mold. It would probably buckle like a house made of cards. I wish there was some sort of inflatable bladder I could inflated and then just deflate after cure and pull it out. Or I might just use some bigger field stones I have as a filler to save on concrete. I figure if I use the right M5 or M7.5 mix, the cement cost would be about 10k. I have all the gravel, just need maybe 200 yards of sand or so which isn't too expensive, maybe 4k delivered.



As far as bracing the steel. Perhaps so, but 1/4" plate is pretty stout stuff. They make Buckets for skid steers out of lesser thickness, although it is braced in corners for wear and they do have a 1/2 to 3/4" cutting blade to take the brunt of the force.

Where I am worried most about bulky bracing would be between the barriers because that would increase the gap between the teeth. That's why I was leaning toward steel in a cast-in-place scenario. Where I would be the most worried about a bow-out would be near the bottom of the mould. I could always weld a few 2.5" by 3/16" thick oil field pipe across the sides on on the verticals to discourage the plates from bowing when the 4000lb mix is dumped in.


I am using a fractured rock type of aggregate that is very angular and stacks, stands on itself nicely vs smooth gravel that would want to ooze out the bottom if it could.
 

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retired framer
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Hammered Thumb
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I don't follow how you are affected by the taxes, and how being movable negates that. If your total assessment goes up from overall improvements, so be it. But wooden fences are movable too. A 6' high concrete fence, is a fence, is a fence.

You plan to cast-in-place one 4' wide section, then pour next to it, so a reusable form with sides can not be used. You'd have to pour every other one then build a form between them, and you'd have a cold joint or even could place an expansion joint, but you won't be able to slide one out with either.

If you precast somewhere else on site and move them, good luck with that size and a chain/strap hanging from bobcat bucket. Do you know how to reinforce them for the hooks, as slots at the bottom won't do at 6' tall.

Rebar - you'll need it.
Insulation - not a good idea as filler, as you have to tie across it.

Precast - better to cast laying on its side or upside down with that shape.
Footing - you'll probably have difficulty lining them up plumb, can't shim with gravel.
Lateral loads - need to be buried and/or tied to footing. Have you done the calcs to make sure they won't topple over? Will each panel be tied together with a pin (like highway barriers) or welded (like precast tilt-up)?

As easier time would be with CMUs, you can follow a step-by-step guide, here's an example: Fences in Scottsdale AZ

You could even try ICF (with stucco face) being a lot easier if you just have to pour something.
 

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You can use 3D Panel like Tridipanel they are for concrete to spray applied on both sides. You can order in many thickness & lengths. I have installed them 22 ft. tall with no problems.
Also they were used for band walls (revetments for dirt & rock for loader pick up )
Build two of then 3 feet apart than fill the center with dirt / sand no body will be able to put a dent in them.
 

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Discussion Starter · #12 ·
Hopefully you're gonna make these much shorter than a temporary jersey barrier section, because I don't think you'd move one of those with your Bobcat.
Well, the Goal is to cast them in place so I don't have to move them. Moving something like this across an uneven field with a tracked machine ... not ideal, hit one rock and you feel like you are on a see-saw with Dumbo on the other end.

I figured, these would weigh about 4000 lbs dry. I would be at the upper end of my bobcat capacity, well past the 50% tipping load. I could pick it up at full rev, but wouldn't want to do that very often and I would be carrying these things low. Here's how I am figuring that.

I figured, 6' high, 4' wide, 2' deep at the bottom tapered to 6" at the top.

(This shape mimics a self-standing stone wall 'battening', or tapering, I could make the top 12" but that would be more concrete.)

Lets do some math:

Area of Trapezoid, side view:

A=((top+bottom)/2)*height = (2+.5)/2 * 6 = 7.5 sq ft side area

7.5 sq ft side area * 4 feet wide = 30 cubic feet / 28 cubic feet per yard ~ 1.07 yards. Wet concrete weighs about 4000 lbs per cubic yard.

4285 lbs barrier weight, but will lose weight as water dries, it could weigh around 3900 lbs when fully cured.

Bobcat T650 Lift Capacity at 50% tip: 3670 lbs

Worst case, I just get a bigger machine to lift.
 

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Discussion Starter · #13 ·
If you put pavers on the ground, they are not permanent. They can be moved. They are not 'in the ground'. A Fence has posts that are in the ground. Same thing with this, if it's not in the ground, it's not permanent. I could even make the case that this is my side business and the sides of my property is where I am stocking my supplies. Hang a for-sale sign on them and what can they say. They can't tax me on unsold merchandise. I could demonstrate any time they wanted me lifting up one of these and loading it on a trailer for sale. We all know Vegas always wins, but according to their definition of what is permanent and what is not ... I should be able to beat they odds.

As far as squeezing the moulds tight together and not being able to brace, I don't think the blow out lateral side force is going to be be as great as the blow out force on the 4' front and back sides. If I used 1/4 plate welded steel on the sides, then that should be able to hold the side pressure and this would allow me to get the molds within 1/2" to 1" of each other. If it left a 2" gap between the molds that's not bad. My dog couldn't escape , and would give him something to look through and bark at stuff on the other side. I could always plant some sort of hedge on the other side, or cactus patch if I wanted more privacy, or just fill the voids with some gravel. If I used strictly wood for moulds, I would agree with you that I would have to brace the hell out of the plywood at the bottom. I might be able to make a hybrid with plate steel sides, and wood front and back.

If I casted them in place, I wasn't planning on using any rebar or hooks to move them. I could just put my palette forks under the mold and pick it straight up. If I worried about it rocking, I could pallet strap it to the forks. Might have to rig up some sort of camera system to safely transport it. As far as reinforcement, I am hoping I won't need any as these are solid blocks.
Worst case I was thinking about cutting up the field fence I have with an angle grinder and dangling it in the center of the mould (wrapped around a pipe spanning the top and hog-ringed to hold) as a fabric to help the strength of the concrete.

For lining them up, I was going to stretch a wire with a come-along. As long as these are above grade pours, I can get pretty close. A wood mold would be easier to "walk into place" with human hands, but forget it with a plate steel mould weighing about 1000 lbs.

As far as toppling over, it's like a weeble wobble. Heavier at the base than the top. This is how dry stack walls are made. If a larger vehicle hits it, it most likely will go over, but so will a speed block wall too. If I were to embank some dirt on the opposite side as the impact force, and water it down, I don't think it's going anywhere. I've had a 6" rock embedded in the road caliche out here stop my John Deer 325 wheeled loader cold and stall the engine out when the bucket hit it. I built a rock gabion about the same shape, it was much longer (12') out of oil field pipe and woven wire field fence and dumped about 10 buckets of rock in there. It's not going anywhere, if a car or truck it ... I think the passengers wouldn't make it.

I love CMU's and ICF, but they are pricey. Lots of prep work with foundation and then there are heavy taxes for valuation plus all the time to correctly lay the block wall. If someone hits it, it's a big mess to fix. I'm trying to avoid all that. I'm crushing up (MBL-140 bucket crusher) the field stone that I got for free from pools, septic tank installs, and other construction sites. I used the dirt to maintain the non-county maintained roads leading to my property.

I don't follow how you are affected by the taxes, and how being movable negates that. If your total assessment goes up from overall improvements, so be it. But wooden fences are movable too. A 6' high concrete fence, is a fence, is a fence.

You plan to cast-in-place one 4' wide section, then pour next to it, so a reusable form with sides can not be used. You'd have to pour every other one then build a form between them, and you'd have a cold joint or even could place an expansion joint, but you won't be able to slide one out with either.

If you precast somewhere else on site and move them, good luck with that size and a chain/strap hanging from bobcat bucket. Do you know how to reinforce them for the hooks, as slots at the bottom won't do at 6' tall.

Rebar - you'll need it.
Insulation - not a good idea as filler, as you have to tie across it.

Precast - better to cast laying on its side or upside down with that shape.
Footing - you'll probably have difficulty lining them up plumb, can't shim with gravel.
Lateral loads - need to be buried and/or tied to footing. Have you done the calcs to make sure they won't topple over? Will each panel be tied together with a pin (like highway barriers) or welded (like precast tilt-up)?

As easier time would be with CMUs, you can follow a step-by-step guide, here's an example: Fences in Scottsdale AZ

You could even try ICF (with stucco face) being a lot easier if you just have to pour something.
 

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Discussion Starter · #14 ·
Those a pretty cool Clarance for homes, like some sort of ICF. Probably pricey panels. Do you know what they go for per square foot for the wire on foam panels? Seems there are some upright column supports they are sandwiched between?

I would have to put something like that on a footer and tie into that. I am trying to avoid that for taxation and expense.

If I tried to use them as some sort of A-Frame wall, One thing we have out in AZ is Packrats. They would tunnel into that Foam and there would be plooms of white foam blowing out into the yard in a matter of weeks. In a years time I would be overrun with an unstoppable infestation.

I'll believe in that product when they start using it as a highway retaining wall and it lasts more than a year.

You can use 3D Panel like Tridipanel they are for concrete to spray applied on both sides. You can order in many thickness & lengths. I have installed them 22 ft. tall with no problems.
Also they were used for band walls (revetments for dirt & rock for loader pick up )
Build two of then 3 feet apart than fill the center with dirt / sand no body will be able to put a dent in them.
 
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