Exploring Boston Valley’s Four Forming Methods for Efficient Fabrication
The inherent malleable property of terra cotta is unique, allowing it to be manipulated and fabricated for architecture in multiple ways. Boston Valley Terra Cotta is the world’s only architectural ceramics manufacturer that employs four distinct forming methods in the creation of our products. This multi-process approach, coupled with the high plasticity of the material, allows us to fabricate a versatile range of architectural terra cotta products, from flat TerraClad® rainscreen panels and roof tiles to complex masonry profiles.
The forming method used for a project is determined by various factors, including the architect’s design intent, the building’s structural system, and the size, shape, and quantity of units needed for production. Below we define the four forming methods to explain how Boston Valley manufactures terra cotta for your project.
Extrusion
During this forming method, clay is pushed through a steel die by a powerful extrusion auger to create a linear profile with a hollow cross section. Units are then cut to the desired length. The extrusion method is used to create many duplicates of the same profile piece. It is the quickest and most efficient method for producing architectural terra cotta building components, particularly for large quantity of blocks with the same profile and long continuous spans of panels.
Extruded Units — Left: One Vanderbilt; Right: The Bechtler Museum of Modern Art
The One Vanderbilt building in Manhattan, designed by Kohn Pedersen Fox Associates, is an example of a project that required a significant number of units — we manufactured over 140,000 SF of terra cotta for the exterior façade. As extrusion is a very cost-effective method of clay production, it was ideal for producing One Vanderbilt’s profile units in large quantities. Boston Valley manufactured all 42,000 of the white terra cotta spandrels that climb up the building’s façade, along with 2,500 soffit panels that are installed both in the interior and exterior of the supertall tower.
The terra cotta spandrels created for One Vanderbilt were extruded with a concave shape, creating scalloped contours that catch and reflect the sunlight when assembled. The corners on the outer terra cotta field panels were then custom cut post-extrusion to accommodate the facade’s gradual changes in dimension as it ascends the building.
Extruded Units — Left: Connecticut College New London Hall; Right: 512 W 22nd Street
Hydraulic RAM Press
Hydraulic RAM press method is considered most efficient for producing high quantities of non-linear terra cotta components. RAM press production is comprised of a two-piece mold — a steel die case that contains the block’s negative shape — and a hydraulic press. A clay slug is placed between the die and then pressed into its form. The RAM press forming method is used for less sculptural terra cotta pieces or simple units without an undercut.
RAM Press Units — The John and Mable Ringling Museum of Art – Center for Asian Art
The John and Mable Ringling Museum of Art – Center for Asian Art is a signature building designed by Machado and Silvetti Associates. Boston Valley worked with the architect to manufacture the deep green TerraClad® façade on the 7,500 square-foot expansion. 90% of façade was produced from 2 dies using the RAM press forming method. In total, 10 unique profiles comprised the façade design; corner profiles were manufactured using the hand-press and slip-cast methods and custom cut RAM units for a precise fit.
Slip-Cast
Slip-casting is used when fabricating architectural terra cotta with highly detailed forms that have ornamental shapes and undercuts. The slip-cast process begins by pouring liquid terra cotta “slip” into a plaster mold; the plaster draws moisture from the liquid slip and deposits clay on the plaster walls. The excess liquid is evacuated, and the mold is removed, resulting in a fully formed masonry unit. While time-intensive, the slip-casting process beneficial when considering material and weight: using a liquid form of terra cotta results in a thinner wall, making for a lighter, more detailed piece. Slip-casting is primarily utilized on projects with ornamental terra cotta pieces and units that require a hollow interior for production and anchoring purposes.
Slip-Cast Units — Left: 7 Gouverneur Slip East; Right: Upper East Side Townhouse
Hand-Press
Traditional hand-pressing is the original manufacturing method of casting architectural terra cotta. Hand-press is a labor-intensive process whereby clay is packed into a multiple part mold with an open back. Molds are filled with clay by hand and pressed with rubber mallets against all five faces of the mold to a set thickness. Hand-press is specifically used for sculptural pieces that contain non-linear detailing or details with undercuts. This method is best suited for unique, small quantity pieces and one-offs, as it requires skilled sculptors to hand-finish each piece.
Hand-Press Masonry — City College of NYC
All Together Now
On occasion, all four forming methods can be found in-use within the same building project. This was the case in when recreating the masonry for 168 North Michigan Ave, where the full complement of techniques was combined:
- Extrusion
- Hydraulic RAM Press
- Slip-cast
- Hand-press
All four forming methods were used in the restoration of 168 North Michigan Avenue.
Another prime example of a project that used all four forming methods is the Fitzroy in NYC. Boston Valley Terra Cotta manufactured 5,600 terra cotta blocks out of 500 unique forms. Through the different methods of fabrication, we were able to produce the collection of custom shapes necessary to create this elaborate façade.
The benefit of utilizing multiple forming methods for terra cotta manufacturing is that it gives our facility the flexibility to accommodate different production needs, from high quantity yield to high detail yield. The architect is then able to focus on designing for form and construction cost, while Boston Valley determines the most appropriate fabrication method(s) for the build. Extrusion and RAM press enable us to manufacture many units with maximum efficiency when a project calls for it, yet we can easily pivot to create sculptural, ornamental pieces using the slip-cast and hand-press methods.
Contact a representative to learn more about Boston Valley’s fabrication capabilities. Our team has extensive expertise in working with terra cotta for any application. We’re ready to partner with you from the start of the design process to ensure a successful outcome. Together, we can take your project into real world manufacturable solutions for a long-lasting terra cotta façade.
