Types of Forms for Pouring Concrete Walls

Wood Slab Forms

• Builders make wood forms on the construction site using timber and plywood or particleboard that's resistant to moisture. Wood for forms needs to be straight, strong and only partially seasoned, according to Construction Knowledge. If the wood is kiln-dried, it may swell from contact with water, developing bulges and becoming distorted. The website Construction Knowledge recommends softwoods, such as fir, pine and spruce because they are economical, light and easy to work with. Wood forms are easy to make and easy to adapt to any shape, but making them takes a lot of time for large buildings. When the concrete is set, the forms are removed, and can be reused at least a few times.

Metal Framing

• Metal modules, usually made of steel or aluminum, are prefabricated and can be quickly assembled using clips, pins or screws, saving time at the construction site. Metal framing is also removed after the concrete sets and can be used many more times than wood forms before needing to be replaced.

Insulating Concrete Forms

• Insulating concrete forms consist of heavy-duty, yet lightweight, foam blocks that interlock using rebar to form a structure with two sides of foam and a hollow center for the poured concrete. The forms remain in place, so the walls have the insulation built into them and have a high thermal resistance, usually with R-values above R-17, according to the U.S. Department of Energy. (R-values are a measure of a material's insulating ability.) The walls are also strong and can tolerate high winds and extreme temperatures.

Considerations

• Another, relatively new, type of form for pouring concrete walls is reusable plastic formwork. These systems are interlocking and modular, and they are lightweight, easy to assemble, strong and reusable. Plastic forms cost less than metal and are stronger than wood. Plastic can also be used many more times than wood, saving natural resources, and works especially well for mass housing projects, especially when cost is a factor.