I am going to use “Quikrete” 8″ concrete form tubes but am looking for guidance on how best to use them. I am builidng a small shed which is attached to the house on one side and on 4 posts on the other. I want to ensure that it doesn’t move so I have dug 4 10″ holes 48″ deep. I am ready to begin filling the concrete form tubes with the concrete but do I need to worry about movement of the tube? What is the best way to fill the tubes? Should I back fill around the tube prior to filling with the contrete? Any help would be appreciated!!!
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I quit using cardboard tubes about 3 years ago when I found I could buy the ribbed black plastic culvert (smooth inside) for nearly the same price. It comes in 20' lengths but can be cut with a handsaw. I rip them down one side with a skil saw then tie them closed with plastic cable ties.
The nice thing about them is you can screw bracing into the ribs when their plumb. And when your mud has set, cut off the ties and the tubes can be re-used.
I think the smallest size is 8" diameter. I've poured columns 12" X12' with no problems. If you want to backfill and leave them on, they protect your concrete.
I get my culverts at a local logging supply.
Not sure of the manufacturer, but I`ve seen prefabbed plastic footing forms, (Boots I think theyre called) that the sonatubes sit inside. Set them on a gravel base, backfill and poor. I`ve seen them advertised in FHB.
J. D. Reynolds
Home Improvements
"DO IT RIGHT, DO IT ONCE"
I prefer to backfill my tubes before filling them (using a pointed spade). Just make sure they remain plum while backfilling.
When we used Sonotubes, we always staked a few posts into the ground next to the tube, then screwd 2X4 bracing to the tube and to the stakes so to keep the tube plumb and in position. A real easy way to do this is to lay a 2X4 rail on each side of the tube ( the 2x4s are running parrellel to each other). run a few screws into the sonotube and the 2X4s. Now drive 2 stakes in the ground for each rail and screw these to the 2x4s. To further lock in the tube, toenail 2 short cross braces running perpendicular to the 2x4 rails. These crossbraces sit on top of the rails and are also screwed to the tube. Your tube will now be anchored plumb at the top. Do backfill the bottom of the tube about 1/3 of the way up for added stability.
When pouring, pour slow and steady, don't just dump it If you have more than one tube to fill, then partially fill one about 1/3 to 1/2 way, then go fill anotherone or two tubes about the same amount before coming back and finish filling the first one. This gives the tube a little time to settle and anchor itself.
Davo
Maybe this is a dumb question, but why bother with tubes? Sonotubes are expensive, aren't they? Why not dig a hole with a post hole digger and fill up the hole?
Why is the third hand on a watch called the second hand?
If you drill the hole extra deep, you can cut the excess length of the hole off and use it for above ground elevation. I've been trying to sell this concept; you see, I've got a dried up well that's about 300' deep which should be good for at least 100 post holes...
Interesting concept. I've heard that there was a good market for used postholes, but have never tried to tap it myself.
Dear Abby, My boyfriend is going to be twenty years old next month. I'd like to give him something nice for his birthday. What do you think he'd like? From Carol
Dear Carol, Never mind what he'd like. Give him a tie.
Look, the code says 42" and I am putting gravel beneath it, that's the reason for 48". I want the concrete below the frost line to avoid heaving.
Davo, thanks for all your detailed information! I will be putting it to the test this weekend. I really appreciate your insight.
Why 48 inches deep, unless you live in Alaska?
You only need go below the frost line.
You are not planning to have footers, I gather.
Depending on your soil, an 8 inch pier (with about
a half square foot of bearing area) may only have
500 pounds of weight capacity. Your building may
sink excessively. Minimum footer diameter is 18
inches around here. If the shed is attached to the
house, that is what will keep the shed from shifting
sideways or backwards. I would re-think this a bit
before pouring concrete. I personally would not place
piers without footings unless it's just a little
garden shed and you don't care if it settles. Dig ####24 inch hole. Pour a 4 inch or 6 inch slab
at the bottom (no form needed). Set the sonotube an inch
deep into the wet concrete and brace while curing.
Backfill and trim the tube to length. Fill sonotube
with concrete. Yes, there's a lot of digging. That's
why people invented backhoes.
Not sure where you are in the country but here in NY you need to go down 42" to meet code.
J. D. Reynolds
Home Improvements
"DO IT RIGHT, DO IT ONCE"
Edited 6/6/2002 9:32:28 AM ET by JAYBIRD
Obviously, I'm much further South. Only 24 inches here.
Didn't know frost was that deep up there. Anyway, the
footer diameter needs to be substantial, like 18 or 24
inches. If he could dig a 4 foot deep hole with a
posthole digger, I'd bet the soil is pretty easy. Can't
possibly do that here, and they still require 18 inch
diameter minimum footings.
Try Bigfoots http://www.bigfootsystems.com I think
IIRC, there are places in Montana that specify 60", and that's not even in the mountains.
Bob, the soil here is a pretty tough clay. I took a LONG time to dig these bad boys. I obtained a building permit from the city and specifically asked if the 8" sonotube was sufficient and they stated yes. Since I am down 48", I could widen the hold at the bottom, and add a footer. Suggestions for the depth of the footer?
Well, if the inspectors say it's OK, then it's OK.
You could have soil with really good compression
characteristics. When in doubt, its best to assume
the worst. If you want to bell the bottom out for
a footer, I'd go 18 inch diameter. A bit tricky
in a narrow hole. With 10 inch holes and 8 inch tube
you can easily shift the tube a couple inches to make
pier about where you need it. 6 inches is a good thickness
for an 18 inch footer.
An 8 inch diameter footer is only .35 square feet.
a 18 inch is 1.75 square feet. 5 times the capacity.
an 8 by 16 room is 128 SF. at 100 pounds/SF live plus
dead load, that's 12800 pounds. Half on the house,
half divided among 4 piers gives 1600 pounds per pier.
So, with crummy soil (1000 PSF), you want about 1.6
square feet of bearing. A rough example of the sort
of calculation you want to do. You could have 5000 PSF
soil. If so, 8 inches would work. Don't know that I'd
want my house built that way, even if the inspectors say OK.
The pier diameter is not a problem. Concrete is good for
1000 pounds per square inch or better.
If you are below the frost line, you should be fine. Widening the bottom of the hole won't hurt ......... it will increase the bearing capacity of the the pier. I'd add some #4 rebar to the piers. Concrete has good strength in compression but is poor in tension .......... I've seen piers in my area cracked in half from the frost working on piers with no rebar in them. Check out the Simpson catalog at your local lumberyard. I'm not sure how your shed will sit on your piers (posts?), but chances are Simpson has a connector that you can set in your piers when pouring. To calculate how much concrete you need:
Multiply 3.1416 x .1111 (assuming an 8" sonotube) x the depth of hole in feet x the number of piers. This will give you an answer in cubic feet. Divide by 27 if you want cubic yards. This will not account for any extra if you widen the bottom of the hole and it does not take into account for waste.