Forms for Retaining Walls

Basic Construction

• The retaining wall is seated on a concrete-filled foundation trench, which is usually about 3 feet wide or so and 12 inches deep, although these guidelines may need to be adjusted for specific projects. The L-shaped foundation helps to hold the wall in place against the force of the soil on the slope. Rebar runs through the footing into the wall to keep the two connected. It's important to make sure the earth side of the wall has proper drainage so water doesn't accumulate behind the wall and cause problems.

Forms

• For relatively small projects like retaining walls, forms may be made either from wood, engineered wood with wood in a metal frame or solid metal. The type you use depends on the size of the project, because the whole purpose of the form is to hold the concrete in place while it solidifies, and the more concrete you have, the sturdier the form you'll need to keep it in place.

Types

• For a very small retaining wall less than 6 inches in height, wooden boards attached to stakes at regular intervals may often be sufficient. Wooden forms like these are simple and easy to assemble but not very strong. Larger walls require sturdy wood formwork or engineered wood and metal forms held together by pins, latches or similar fasteners. The engineered wood and metal forms are prefabricated rather than constructed on-site and will cost more than simple plywood and nails.

Considerations

• Plywood is more flexible than prefabricated formwork, which may be beneficial for sections of the retaining wall that are more complicated or need to round a bend or a curve. The formwork will usually need to remain in place for more than 24 hours after the concrete is poured. At that point, the forms can be removed to leave the set concrete exposed. Depending on the type of project and the amount of concrete, the forms may sometimes need to remain in place for a longer period of time.