Concrete form tubes are made of high strength, water-resistant paper. They are designed to allow you to dig post holes and set your tubes and pour concrete into the forms all in one day. The durable tubes are of particular advantage in rainy weather when pouring concrete into an unsupported dirt hole would be ill advised. In locales that experience cold winter weather, concrete footings must extend at least 12 inches below the frost line, measure 8 inches thick or more and be twice as wide as the posts they will support. Using a tube to fill concrete posts helps you to meet required code without wasting concrete in the process.
Contact your local building inspector for information regarding the frost line in your area.
Measure your tube so that it will extend 12 inches or more deeper than the frost line. Remember also to allow for the height above grade that your post must be for your building project. Cut the tube to length using your hacksaw.
Drill your hole to the proper depth using your power auger, or dig it with a shovel. Remove the auger and set it well away from the hole.
Toss a 4-inch layer of gravel into the hole to aid drainage.
Insert the tube into the hole until it rests firmly on your gravel layer. Pack soil around the tube to keep it upright.
Mix your concrete mix with water according to package directions. A rented mixer or wheelbarrow, with a mixing drill or shovel to mix, will help you achieve the proper consistency.
Check for level and plumb of the tube and have an assistant hold the tube in place during the pouring process.
Pour the concrete into the tube. Use a piece of wood to mix the concrete every two feet or so until the tube is filled.
Apply water to the tubed footing to keep it damp for 48 hours while the concrete inside cures.
Backfill the hole with the remaining dirt and cut away the exposed paper tubing using your utility knife. Your footing is now complete.