Fabric forming is one of the easiest and cheapest ways to form concrete. Instead of time consuming and costly wooden or metal forms, you use little more than a plastic or similar fabric. The end result is not only aesthetically beautiful, it is also stronger, because it lends itself to rounded shapes, compacted pours, and consistent curing.
The basic principle is simple. Cut your fabric to the required size, attach it to something solid which is then braced to hold it in place, add reinforcement and pour the concrete into the flexible form.
Many shapes and uses can be created with this method, but we will focus on a simple column. You can use this system for standalone columns or posts, or for posts that attach to an existing wall. We will describe a standalone post, as this is a little more difficult.
2 pieces of 1”x4” lumber. The length is determined by the height of the post you wish to make.
Metal reinforcement, the length of which is determined by the depth of the base plus the height of the post.
Plastic or tarp (a vinyl tarp is best, as there will be no stretching).
Concrete (cement, sand, gravel, water).
Metal or wooden boards for bracing.
Post-hole digger or rock bar
Concrete mixing tools
The size of your form will depend on the size of your post. We will describe an 8 feet tall post, 8 inches in diameter. Adjust your dimensions according to your own needs.
There are all kinds of things you can do to a fabric form to make the end result more interesting. Any wrinkles or restrictions of the tarp will be transferred to the concrete. For example, if you weave string across the tarp when it is empty, the concrete will bulge out around the string, leaving a weaving pattern in it when you remove the form.
If you use a sturdy, thick plastic and keep it out of the sun during storage, these forms can be reused several times, reducing waste and cost. Old tarps or awnings are good sources of fabric. Look for woven fabrics for interesting textures and strength. Staple areas are famous for stretching, so we usually double or triple fold the fabric here to help make it last longer. Nails with washers might be better. Small holes are not a problem, so get creative with your fabric!