Watching DIY network, I notice that when pouring a pier for a deck post or similar, that a tube is often inserted before the concrete is poured.
I just pour the concrete directly into the hole left by the auger or post hole digger. Other than the neat top visible sticking out of the ground, is there a purpose to the tube?
I see the tube and wonder how I'd fill the dirt tightly around it again and that it'd be "tippy". If I pour right into the hole, then the dirt will be tight around the concrete.
Te tubes are sonotubes. "Sonotubes" are a patent namebrand but others offer the same as Tubular concrete forms. They don't usually set up on top of the ground. A portion is in the excavated hole. Typically they are used to pour piers to a desired heigth. Construction begins on top of them with a fastner suited to your needs. It also allows wood to be elivated above the ground to prevent rot. They are an alternative to laying concrete block piers.
Sure... But why the tube all the way to the bottom of the hole? Why not just fill the hole with concrete without a tube?
You can certainly do that. They also make a base that can go down at the bottom to spread the load out further. I've used them on footers for the last foot or so to give me a finished look above grade. I like to have the concrete come above grade and the wood posts mounted to a post mounting bracket to keep it off the concrete. The posts last longer if they aren't in the ground.
Any advice given here is general in nature and is not necessarily valid for your given area. If in doubt check with your local codes enforcement department for what is required when doing electrical, plumbing or structural work on your house. Permits may or may not be required in your area and home owners may not be able to DIY some tasks. I have no way of knowing if you have the skills needed to complete the tasks you are asking about, when in doubt seek professional assistance.
My advice may be worth exactly what you pay me for it. :-) For the record I did not stay in a Holiday Inn Express last night.
That is just to stabilize the tube. It does not go to the bottom. May I ask why you are inquiring or what you intend to do with the sonotubes?
I did what Sparky above said, I used tubes on the last 8 inches or so of the base to make the top neat and pretty. I also figured it would keep dirt from touching the post and prolong the life of the post.
I did this on a backyard pergola.
Just do show the finished product.
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