Unlike most insulating concrete forming systems, which sandwich cast-in-place concrete between interior and exterior layers of insulation, the Thermalwall building system uses 4-inch-thick extruded expanded polystyrene panels to form only the exterior of the concrete wall. For the inner formwork, contractors can use standard 2x8-foot plywood, aluminum, or steel form panels.
The key to the system is a specially designed polyvinyl-chloride connector made from recycled vinyl-window scrap material. The connectors act as a tie mechanism, holding the 4-inch-thick foam panels in place during wall forming. They also serve as a water barrier and thermal break at the vertical joints between form panels and as furring for attachment of siding or other exterior finishes. On the inside end of the connector and running its full length is a round bulb that's notched to accept modified steel form ties. The end of the tie that fits into the notched area has a hole in it so a steel pin can be dropped through the tie and connector to join them. The other end of the tie is designed to fit the latching mechanisms of standard wall-form panels.
Once the forms are erected and all the concrete has been placed and reaches the required set, workers can remove the interior form panels for reuse on another job. The foam insulation and plastic connectors remain in place, ready to accept most exterior siding materials. On the interior, the walls can be finished with a thin coat of plaster or left exposed.