You can use fiber form tubes, or tubular forms, as they are also called, to form concrete into piers or support columns for your backyard projects. In some areas, these tubes are a boon because the soil is too sandy or too granular to provide solid walls of support for concrete poured into the ground. In other areas, construction codes may require that you use fiber form tubes.
Determine the length of tube needed for your project. If you plan to extend the fiber tube any distance above the ground, have the same amount above and below ground. For example, if the concrete pier extends 24 inches above ground, be sure 24 inches are below.
Cut the tube with a handsaw, making a square cut, to the length you require. Stores normally sell fiber form tubes in 48-inch lengths, but 12-foot lengths are available.
Place the form in the hole, suspending the bottom of the tube a few inches above the bottom of the hole so that the concrete, once poured, can spread below. Pour the concrete into the tubes.
Insert rebar--steel rods with ridges--in the hole 3 inches apart to reinforce the concrete. Deck posts usually need a couple of pieces of rebar.
Sink treated wood into the tube if you plan to embed the post in the wood, rather than fastening it to the top.
Level off the top of the tube to create a flat surface if you plan to fasten a post with bolts to the top later.
Let the concrete harden before removing the fiber above ground. Let the concrete cure for a week before you bolt anything to the top.
Determine the frost line for your part of the country. If the pier doesn't extend below the frost line, winter freezes could push the pier up so much it could damage the deck.