A few weeks ago, after the excavation was complete and the gravel bed tamped level, the Charles W. Weaver Masonry Company moved in to erect the basement of a 28 by 36-foot home near here. Just 75 minutes later the carpenters moved in to attach the sill plates and begin erecting the house proper. More than 8,000 square feet of wall were in place in little more than one hour. It was that fast.
What made such remarkable speed possible is a new concept in basement walls (or the walls of earth-sheltered homes). It involves the erection of precast, insulated concrete panels that Melvin Zimmerman, Melvin Weaver, and Leon Martin of this Pennsylvania Dutch region have spent the past 41/2 years developing. They call them Superior Walls because beside the speed with which the panels can be erected, they offer greater strength and resistance to water penetration than conventional systems.
Until now, pressure-treated wood was the only alternative to poured concrete or concrete block for basements. There had to be a better way, the trio agreed, and some four years of trial and error -- and what is known around here as ``good old Pennsylvania Dutch ingenuity'' -- finally produced the new system and their company, Superior Wall, of East Earl, Pa.
Conventional wall systems involve pouring the footings, erecting the forms, and then pouring the walls or else building them with concrete block. All this work can consume the better part of a week of construction time even if the weather is cooperative. These walls are notorious, too, for cracking and leaking water.
With the Superior Walls, on the other hand, exterior sealant is deemed unnecessary for several reasons:
The dense nature of the concrete. (The panels have a compressive strength above 5,000 pounds per square inch to as high as 7,000 p.s.i. compared with conventional poured concrete at 2,000 to 4,000 p.s.i.)
The fact that the concrete is bonded to rigid polyurethane insulation, which adds both a vapor and waterproof barrier to the panel.
The triple band of polyurethane caulking applied where each panel is joined.
According to a report in the March 1985 issue of the New England Builder, the system should have no water problems if applied with a conventional crushed-stone draining system, but the report suggests that people wanting earth-sheltered housing might feel more confident if an exterior waterproofing membrane were also applied to the exterior.
Tests by Atec Associates Inc. of Baltimore show that the system meets all requirements of the American Concrete Institute.
Typically, a truckload of panels arrives at the building site in the early morning. Using a crane, the four-man crew places the panels (usually 8 to 10 to a house) on a gravel bed. Within two hours the panels are in place, caulked at the seams, and bolted together.
The on-site materials cost of a Superior Wall is some 10 percent higher than conventional concrete or concrete block, but the quick erection and considerable savings in labor costs produce a less expensive end product.
Panels that include R5 foam insulation board are cast on reinforced concrete studs, 24 inches on center. These studs contain preformed holes so plumbing, electric wiring, and television cable can be easily placed and hidden from sight. A pressure-treated nailing strip in each stud makes for easy finishing of the interior. The 71/2-inch depth between the studs can be filled with additional insulation to boost the R value of the walls. Door and window openings are readily included in the precast panels.
The concrete panels, which can range from 3 to 10 feet in height and up to 16 feet in length (longer under special circumstances), are cast some 2 to 4 days before delivery to the building site. At the Charles W. Weaver Masonry Company here two or three panels are cast each day. The method is relatively straightforward and any company specializing in concrete or masonry products could readily adapt their facilities to concrete-panel production, according to Mr. Weaver.
The three inventors are confident of the spread of the system because, as they see it, ``it produces a better product for less money.'' Although designed for basements, it is also being considered for above-ground installations.