Making a new shooting bench

Kevin Stenberg

Well-Known Member
I have intentions of making a concrete shooting bench top. It will be 4" thick with reinforcing mesh in it. I am going to dry stack concrete blocks as a base for the bench. I was wondering. How much overhand of the concrete top can i safely have unsupported by the block base?
 

Ian

Notorious member
Depends on how well you reinforce it, the PSI of the concrete, and how you cure it. I'd use 1/2" rebar in addition to the mesh and place the mesh/rebar at the upper third of the layer. If you do that and keep it covered and wet for the first few days while it cures, a 16" cantilever should be possible without developing cracks.
 

fiver

Well-Known Member
and how many/large your pedestal is will also determine what you can get away with.
16x16 blocks will allow you to cantilever out wider than those 8x12 cinder blocks.
2 legs will span between them further but with less overhang.

our legs are set in a double diamond shape and have bench tops a bit over 4' wide.
they were poured in one single pour with the top as were the sold block type seats on either side.
the right side is wide enough to shoot right handed, or spot for someone, on the left side of the bench.
 

Kevin Stenberg

Well-Known Member
I was way off base. I was thinking even a 4" overhand was on the big side.
All of the table top except the edging will be sitting on concrete blocks. The only edge that i was going to extend more than 4 " was the side that a person shoots from.
 

Pistolero

Well-Known Member
Understand that concrete is strong in compression, very weak in tension.
In a cantilever bending load, like an overhang, the top surface is in tension and the bottom
surface is in compression. That is why Ian said (exactly correclty) to put the 1/2"
rebar near the top. At the top, the steel will take the tension loads. IF THE PRIMARY
LOAD IS AN OVER HANG.


Our range has these benches and they are about 36" wide and about 4-5 ft long, with about
a 8-10"Wx 24" rounded cutout at the back on each side. They are set on top of a 8" diam
sonotube for each of three legs. One at the front on each side, maybe 6" overhang
and one a the back centered. So in this design, the primary load is NOT the overhang.

In that design, the overhangs mean nearly nothing, the primary load will be the
weight of the concrete and the gear on top. That means bending load between pillars, which
puts the tension side on the BOTTOM, compression on top. So, in that situation, I'd put one (or
two 3-4" apart,) 1/2" rebars with the centerline of them forming a V with the bottom
over the rear pillar and the tops of the two arms centered on the top of the front pillars.
Then maybe one rebar across between the front pillars. And THESE should be near
the bottom, because of the bending load between the pillars.

Sonotubes are inexpensive cardboard tubes, designed specifically as forms to make
concrete pillars. Make the pillar mix a bit wetter than normal and work a rebar up and
down a LOT to work out air. Too dry will make a bad fill. "Too wet" won't be much of
an issue unless you go really overboard.


Dig in about 2 ft or more, depending on frost line, deeper for farther north and set the
tube in hole, jig it vertical and pour full of sakrete. A single 1/2" rebar in the middle would be
good. Cut off the tubes very carefully with a level laid across them, jig them plumb
and pour full, flush tops level before pouring. Make your bench top and somehow
(about 6 men, some straps or ropes and a couple of 6 ft 2x4s should do it) lift into place
on top of the three pillars.

Makes a hell of a solid bench which will last about forever in the weather. Letting
the rebar in the pillars stick out an inch and a half and putting in PVC pipes about
2" long with duct tape over the top at exactly the right location to make sockets. Will probably need a
6 mil poly lined plywood floor on your mold with locating holes for these pipes, made from the
already located rebar pieces sticking out of the pillars so they will guaranteed all line
up right. The PVC pipe makes sockets in the bottom of the bench top to sit on the pins
sticking out from the pillars.

Under a $150 in materials, my guess. 12-15 bags of sack crete at around $6
a bag. maybe 20 ft of rebar. Three $10 sonotubes. And a bunch of work.

If you just put blocks on the ground the whole thing will move around over time.

Free engineering. :)

If you make a T-shaped concrete block support, with a foundation to stabilize it,
say 18-24" concrete footer. Then the overhang can be shortish and the long
way will be on the blocks so no bending load where it would be un supported
between pillars. Probably want to pour a couple of the block cores as pillars
to stabilize them. With that design, minimal rebar near the top would be fine.

If you want, I can post a photo of our benches. Nice not to have anything under
to interfere with chairs and feet.

Bill
 
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popper

Well-Known Member
Bill has it right plus the solotube doesn't leave sharp edges! Might check around to see if a pre-cast Co. makes the tops. Guys that do picnic tables, etc.
 

Kevin Stenberg

Well-Known Member
Bill thanks for all the information! A couple of your ideas i have already considered an am going to do. Core fill several blocks for one. The rerod idea i hadn't considered, but i am going to add it to my plans.
 

Pistolero

Well-Known Member
Good luck. Hope it does what you want. Concrete benches are durable and stable, done right.

Bill
 

Ian

Notorious member
Man, how long did it take you to dig that up? I know I posted stuff in there i'd like to reference but even knowing what day it was posted only narrows it down to 2-3 pages. Maybe you're smarter than me and used the search feature.
 

Gary

SE Kansas
Took much lonnnnnnnnger to dig the holes than look up the post. Yeah, search function is your friend.
 
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Intheshop

Banned
Probably shouldn't post this as it's a touch complex...oh well.

Using 2X4's as the form....on a pce of plywood. I take a 2X6 and cut 20* bevels down each side,can be done with a circ saw. Then,with the same bevel setting,start cutting off blocks of a length equal to the boards width. Once finished,the block is square with bevels on 4 sides,all in the same orientation.

These get "shot" onto the base plywood form. Make a nice pattern in both directions. Leaving about 6 inches between rows. Should be obvious which way the "draft" goes on these blocks. Re "barb" goes in the bttm 3rd or so....

It reduces the concrete (weight) more than you think. Just a nice professional way to go about it. Don't be in a hurry to move or take the form off. Keeping the whole thing wet,after you've finish troweled it will increase the strength,right much. Meaning,hose'r down every cpl hours.

I'd use #3 rebar..... and skip any thoughts of fiber,you want the surface troweled,"hard".... almost to the point of burning it. Make it slick.....and do a nice job edging. Good luck with your project.
 

Rick

Moderator
Staff member
Here is the bench that John (Winelover) and I built. Quite solid, top is pressure treated and stained. Cement top would be great except that pesky lifting it up to put it up there.

Shooting bench at John's=small.jpg
 

Pistolero

Well-Known Member
I don't know. Looks kinda flimsy. Heck, probably collapse if you put 25,000 lbs on it.

:p:)

The disadvantage of a concrete top is you need to protect your guns. I have a piece of carpet cut
to the shape of the bench top that is the first thing out. A wooden top is much more forgiving for
the gun finishes and your elbows.

Concrete does last a long time, though.

Bill
 
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fiver

Well-Known Member
yeah[rubbing my neck]
I don't know how he'd get the front of his truck up there [shrug] but,, well?
they are down there in the mid-south.