Ever wondered how they made those oddly shaped or curved concrete buildings or triangular shapes? It is not a secret and your imagination is the only limiting factor. Money, of course, helps buy materials, but in many cases used lumber or plywood will work just fine. Be inventive. A cardboard tube from the inside of a roll of carpet when cut in half makes a great sluice or chute shape for a fountain or stream. Leftover wooden spools from a roll of electrical cord make a great interior shape for a doughnut-shaped circle. All these things are free if you ask for them. Special materials are also available, such as a product called “movable board,” which can be flexed to achieve nice, smooth curves in the faces of the finished concrete. Take a walk around your local big box store with the idea of finding things that can be used to form concrete. You will be surprised what you find. Empty cubes laid on their sides in the form of a wall make perfect portholes or round window openings. They can be found square, round, triangular or just about any shape you can imagine. You can always make your own shapes too. Let’s see how to form a curved wall.
Starting with a plate on the floor to create the wall shape you want is your first step. Of course, you can’t fold a two by four, so you use a larger piece of wood and cut the shape (or part of it) out of that. If the curve fits into a two by six, design the curve and cut it with a saber saw. If the curve is longer than your board or more than will fit on a two by six, use a two by eight and so on. Once you have cut all the floor pieces, make a duplicate set that will be the top plate of your formwork. Put the pieces in place and fix them to the base or the floor. The curved wall is now much easier to build. Using standard two-by-four lumber, place them as close together as possible along the floor plate to create a curved wall. Install your top plate. Using quarter-inch thick Luann plywood, and starting at one end of your form, attach the plywood to the studs, then gently bend the plywood around the wall. You may want to coat the plywood with form oil before installing and while this does make the installation a bit messy, it softens the plywood and makes it even easier to bend. Attach plywood to every two by four. This adds strength to your formwork and holds the plywood in place while it dries. Once the face shape is complete you can complete the back of the shape and stop your concrete. Odd shapes can be built into the face of the formwork to provide voids in the concrete or holes in the wall, etc.
Freeform concrete can be a lot of fun, but it requires a concrete pump that can fire a concrete product called gunite or shotcrete. Any shape is possible and is limited only by the pull of gravity. Rebar, foam forms, and other items can be used as temporary forms for concrete until it hardens. Inground pools are often made of gunite, which is how they get those large sections and curved wall shapes. It takes a team to use a gunite bomb, but once the basics are learned with enough helpers, you can use one too.
Concrete when suspended in air needs some form of reinforcement to help support the weight of the concrete. If you’re trying to make suspended stairs, for example, have an engineer design the rebar layouts for you. Concrete is very heavy and can cause serious injury or worse if it collapses.
Try to form some small architectural elements in your garden and for them use a redi-mixed mixture in bags. Steps, small walls, a pool or pond, and then move on to larger features. You’ll be amazed at how easy it is to make these fabulous features.
pete ackerson
Your friendly building inspector
http://www.wagsys.com
BICES-Building Inspection and Code Enforcement Software System
