Manufacture of Stamped Metal Siding

6. The stamped metal siding was made the traditional way using gravity drop hammers and cast-iron dies. Photo: Lance Carlson.

After being awarded the contract, the sheet metal company proceeded first with making the cast-iron die sets that were needed for four of the five sheet metal patterns used on the exterior of the building. Two different approaches could be used to make the die sets. Where samples of the historic design have survived in relatively good condition, as with the case of the Hexagon, they can be cleaned and repaired to serve as a three-dimensional model for the casting of the dies. Since the cast iron will shrink in casting as it cools from a liquid to a solid (approximately 3/16" per foot), the new die set will create a pattern that is slightly smaller than the original. This approach, however, is cheaper than the second alternative: creating a model that is 1-1/2% larger than the original, to compensate for the shrinking that will occur when the casting cools. This method may be necessary where the historic pieces are too deteriorated for use as a model; where the historic pattern is missing altogether; or where a precise match is required (such as when only selective pieces on a wall require replacement). In such cases, a drawing of the design to be replicated is first produced, increasing the dimensions to correct for the eventual shrinkage. Then a three-dimensional model of the drawing is constructed in clay, plaster, or wood. Next a cast-iron mold of the model is produced from which the male-female die set used in the actual stamping process is created.

7. The brick pattern was a stock design still available from the company. The description from their 1913 catalogue is unchanged from today.

After each die-set for the Hexagon was ready for use, it was placed into a special press, with the female half set onto a cast-iron bed on the floor and the male half attached to a large, cast- iron hammer, known as a gravity drop hammer, hanging above the press bed. A sheet of metal was then placed over the die on the cast-iron bed, and a press operator released the hammer to drop onto the bed, stamping the design into the metal by the force of the meeting of the die-set (see figure 6). Each of the stamped designs was reproduced in the same metal used to make the original. The stock brick pattern was stamped into 28-gauge galvanized steel sheets measuring 28" by 60" (see figure 7). Galvanized steel is often used for exterior installations, due to its resistance to corrosion. Moreover, galvanized steel is strong enough to produce very stiff sheets of stamped siding in large sizes that can cover a fairly large area with minimum nailing support.

8. The four stamped patterns used at the Hexagon are shown (samples in photograph are smaller than the actual sheet size).

The ornamental frieze pattern, pebbled corner strip, and pebbled band were all stamped into pure sheet zinc. More malleable than galvanized steel, zinc is used when the relief of the design must be deep and sharp. The pieces of the pebbled band measured 13" by 48", and the pieces of the pebbled corner and the ornamental frieze measured 15" by 48" (see figure 8).

The fifth design, the molding that divided the frieze, pebbled band and brick patterns on the building's elevations, was formed on a brake press, which bends, flanges, and folds sheet metal. Twenty-eight gauge galvanized steel was used to produce the 2-1/2" molding in 8' sections.

Wall Repair and Insulation

After ordering the replacement metal siding, the contractor waited approximately three months for its arrival at the job site. During this time, a new metal roof was installed and the walls were prepared to receive the new siding. The total replacement of the siding provided an opportunity to add wall insulation for enhanced energy efficiency. Insulation was installed from the exterior to avoid damage to the stamped sheet metal covering the interior walls and to permit installation of a vapor barrier. This required removal of all the exterior plank sheathing, some of which was also deteriorated (see figure 9).

Removal of the plank sheathing also permitted repair and replacement of some deteriorated original framing, primarily on the south side of the house and at the lower portions of the walls. A vapor barrier was installed against the back of the interior plank sheathing. Sheets of 3-1/2" fiberglass insulation were placed in front of the vapor barrier, and 3/4" plywood was installed as an exterior sheathing in place of the original planks.

The galvanized metal window hoods were also repaired and prepared for reinstallation. The painters removed all old layers of paint with heat guns, and a local sheet metal shop resoldered all their split and splayed joints.

Preparation and Painting of Siding

The metal siding arrived at the job site in several shipments throughout the fall and winter. The owner wanted the new siding painted prior to stopping exterior work for the winter, to avoid leaving the highly visible building in a shiny, silver unpainted condition until spring. Therefore, installation needed to begin immediately in order to be completed before the onset of cold weather. To facilitate this, painters prepared the individual pieces of new siding prior to installation and applied the first coat of paint indoors. [They returned the following spring to apply the second, final coat of paint to the installed siding.]

9. Original exterior siding was removed, revealing the exterior plank wall sheathing, which was also removed in order to install additional insulation and a vapor barrier. Photo: Mary Cay Bartush Jones.

The new galvanized steel siding, the new zinc siding, and the old galvanized window hoods each received different paint treatments. Manufacturers often recommend that new galvanized metal be allowed to weather for several months after installation before being painted, to clean and roughen the metal's surface for better paint adherence. However, several additional preparation steps can be
substituted for the weathering period, as was done at the Hexagon. First, the painting crew wiped each galvanized piece with a non-petroleum-based paint thinner to remove most of the factory-applied oil coating. The pieces then received a wash primer (polyvinyl butyral zinc chromate), which removed the remaining factory-applied oil finish so that paint would adhere to the metal.

The stamped zinc ornamental bands did not have the oily surface coating and, therefore, needed no wash primer. These pieces received a rust- inhibiting primer of the type used on galvanized metal. Both the primers and the first finish coat were sprayed onto the siding pieces indoors. The final coat of paint was rolled onto the face of the installed siding.

Installation of Metal Siding

After the painters prepared the metal surfaces and applied the initial coat of paint, the contractor's crew installed the metal siding. In addition to basic carpenter's tools, tin snips and a brake press were required to complete this aspect of the work. The siding was placed over the air infiltration barrier and face-nailed to the frame walls with #4 galvanized nails.

The pebbled vertical corner pieces were installed first. Since the new pieces matched the original corners, they had been fabricated to fit around the original 7/8" planks. Therefore, the new corner pieces had to be slightly rebent on a brake onsite to accommodate the new 3/4" plywood, backing material.

10. Installation of siding began at the base of each story of the building. Corner pieces were nailed first, followed by the base flashing, and the stamped brick siding. Care was taken to match the patterns from one elevation to the next around the building. Photo: Mary Cay Bartusb Jones.

Once the corner pieces were in place, flashing was installed at the point where the frame walls met the dressed stone foundation. The carpenter's crew bent and formed the flashing in 10' sections on a brake at the job site. Its finished height on the wall was approximately 9-1/2".

The last and largest step of the process was the installation of the brick pattern siding and the ornamental bands sheathing the building's elevations. Using a "story pole" of his own design, the carpenter marked the heights of each siding design on the individual elevations to ensure that the different patterns would be installed at the same locations on every side of the building.

On each story, installation began at the bottom and proceeded upward toward the roofline (see Figure 10.)

Each piece of siding lapped over the piece of siding below it and was face- nailed to the house's wood frame. The siding also lapped over the already installed corner pieces. Since the new sheets and bands of siding were identical in size to the originals, only minor trimming was required.

Zinc, the more malleable metal, responded better to being nailed to the wood frame than did the stiffer sheets of galvanized siding. However, zinc can be easily dented and bent, so it required careful installation. The larger, stiffer metal were easier to install, even though they sometimes buckle in response to spot nailing.

11. Finished appearance of several elevations. Siding has been face nailed to underlaying materials and second coat of paint has been applied. Each piece of siding laps over the piece below it, and all overlap the corner pieces. Photo: Richard Neumann.

In the original construction of the Hexagon, the siding had been installed before the windows had been set into the walls. During this project, the window frames were retained in place, so the new siding was bent around and tucked back alongside them. A quarter-round molding was then installed and the edges sealed with a silicone-based caulk. The window hoods were reinstalled after the siding was in place (see figure 11).

By the time the pre-painted siding was installed, it was too cold for further exterior work. The painters returned in the spring to apply a silicone-based caulk to all of the exposed nail heads and any remaining gaps around the windows. The painters then applied the final coat of paint.