A new system of leave-in-place forms incorporates lightweight insulating panels of expanded polystyrene that: fit together with tongue-and-groove joints that contribute to alignment; provide an added thermal resistance of R16 without requiring a separate construction operation to install the insulation; are held in position with plastic ties to avoid thermal short circuits; are stiff enough to withstand the pressure of a 32-inch lift of 4- to 5-inch-slump concrete; and provide anchorage, through plates on the snap ties, for attaching wall finishing. The walls may be built in a variety of concrete thicknesses from 3 to 12 inches. The forms are used successfully for grade beams, foundation walls and above-grade walls.
Concrete is placed at a slump of 4 to 5 inches in lifts of no more than 32 inches (two form courses). Rodding or vibrating reportedly is not usually necessary because the forms and ties vibrate from the impact of the concrete. The second lift of concrete can be started at the same location as the first after 30 minutes have elapsed. All dowels or anchors for finishes should be installed through the forms before the concrete sets. Because of the insulating value of the forms it is possible to place concrete walls at much lower temperatures than with conventional forms without additional insulation. A simple closure can be made at the top, preferably with insulation. If heated concrete is used, no other precautions are usually required.