Pergola footing

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Old 07-08-15, 06:07 AM
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Pergola footing

Hello,

Question concerning footings. My wife and I are working on putting up a pergola. I have the 12" 4 foot hole dug and and sonotubes ready.
1. when i was chatting with my neighbor about the footings he was saying to simply wet the hole add some water, dump the bag in add some more water and mix it up a little with a 2x4 and follow with the next until at the top. Will this work out do you think? It does sound easier then mixing in my wheelbarrow a bag or two at a time and then shoveling it in but i know what is easy is generally not correct.

Thanks.
 
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Old 07-08-15, 06:10 AM
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While in theory mixing up the concrete in the hole should work, all too often the concrete doesn't get mixed well enough or even enough for it to provide a good footer. This is often done with fence posts and has a high failure rate to go along with it. It is much better to mix the concrete separately and then pour it in the hole!
 
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Old 07-08-15, 07:11 AM
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thanks and that is what i figured. I am down about 48" in ND. do you think I need to go deeper or is that deep enough? I want to be sure i have the footing about an inch or two above ground level too.
 
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Old 07-08-15, 08:17 AM
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That's probably deep enough BUT I don't know what your frost line is so that's just an educated guess.
 
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Old 07-08-15, 08:24 AM
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If you typically get a good snow cover, the 4' is probably well below any frost. if, for some reason, you clear all of the snow away, or get one of those strange years where there is little to snow cover for a long period of cold weather, then even the 4' may not be enough.If that is the frost depth they publish for your area, it is probably good to go.

HOWEVER, frost below those tubes isn't the only risk. Frost is known to gran the sides of the tubes and life them. That is one of the reasons you should have a footing at the bottom of each hole that is wider than the tube. If your holes are wide enough you can pour extra concrete around the outside at the bottom and if you use some rebar you can crisscross it a few inches above the bottom to secure the column to the wider base.

Old school methods that may be worthless or outdated, so lets see if the real concrete pros have more suggestions.

Bud
 
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Old 07-08-15, 02:21 PM
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Mixing any footing concrete in holes in the ground is never a good practice. While it may be quick and easy, the resulting concrete quality will definitely suffer. Such things as pockets of unmixed material and gobs of surrounding dirt being knocked loose to contaminate the concrete come to mind.

For building a permanent structure, I'd seriously consider using elephants' paws at the bottom of each hole (properly trimmed to fit the sonotube diameter). Their conical shape enables a naturally-enlarged concrete base for effective distribution of shaft concrete loads to the soil.
 
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