Can you build a 30-foot-high wall with a form that's only 15 inches high? Partners Jim Grantham and Leroy Gray, of The Gray+Tham Co., Seattle, have developed and patented a method for doing just that. Workers can raise the forms a few inches at a time as permitted by stiffening of the concrete, so lateral pressures never have a chance to build up and form ties are not required. Since the forms can be erected and stripped manually, no crane is needed.
The form is a 24-foot-long box beam made of plywood and dimension lumber. It is 15 inches high, 4 inches across, and weighs 120 pounds. A smooth liner of sheet plastic is attached with screws to the inner form face that contacts the concrete. To operate the system, workers set 6x8-inch double aluminum channel strongbacks the full height of the wall, tied back to stable construction at 6- to 8-foot intervals. Forms are set behind the strongbacks, butted end to end but not mechanically connected. Two workers use come-alongs mounted on the end strongbacks to raise the form sections as concreting progresses.