Terra Cotta Facade Systems Today

Terra cotta facade systems today, the extruded and clip hung ceramic skins that tall building work of the kind Michael Stern pursues now specifies in place of brick or stone, begin in a clay works rather than a quarry, and most of what the finished wall can do was decided there. The material’s long record, from the fireproof tile of the 1880s through the glazed skyscrapers before 1930 and its disappearance at mid century, is covered in michaelsternjds.com’s own page, Architectural Terra Cotta. The material is traced here through the plant and onto the clip, in the order a maker meets it.

The body

Everything starts with a mix of clay and water. A ceramic engineer quoted in the Architizer’s product guide to clay cladding stresses that there are no chemical additives and no fibers to stiffen it, only the processes people have used for thousands of years run with modern equipment, and that different natural clays blended together give fired colors from cream through sand and taupe to a range of reds before any pigment is added.⁴ The fabricator Boston Valley puts the consequence plainly in its note on the material’s revival: clay is pliant when wet and exceptionally durable once fired, so the same body serves masonry units, rainscreen panels and precast facings, and it resists freeze and thaw, ultraviolet light and mildew without coatings.⁹

The die

Modern terra cotta is extruded, which is what separates it from the pressed and hand finished blocks of a century ago. In The Architect’s Newspaper’s account of a Bond Street facade, Boston Valley’s sales manager describes most panels shrinking about seven percent between extrusion and finished size, a rate the firm knows in advance because it keeps the same clay bodies and formulas, and compensates for in the geometry of the die itself.² The architect on that job compared the machine to an advanced version of a child’s clay press, able to produce highly specific shapes and colors.²

Drying and firing

A hollow section holds its shape better than a solid one. The same account describes panels made with a hollow core and internal webs that support a scalloped face, with the back kept flat so each piece can lie level through curing and glazing; the larger and more three dimensional the piece, the more attention the webs and the drying need.² Buffalo Rising’s visit to the works describes a factory closer to an artist’s studio, where sculptors and artisans make traditional ornament for restoration alongside the extrusion lines that produce rainscreen panels, and notes that the rainscreen systems common in Europe for decades were only then arriving in the United States.⁷

Figure

From clay body to crate

1. 01
   BodyThe same clay body mixture and formula is used run after run, so the shrinkage rate is known before production begins.
2. 02
   DieDie geometry is scaled up in software to allow for roughly seven percent shrinkage between extrusion and finished size.
3. 03
   ExtrusionClay is pushed through the die into a long hollow section with internal webs that support the profile and keep it from distorting.
4. 04
   Flat backThe rear face is kept flat so the piece can lie on a level surface through drying and glazing.
5. 05
   Glaze and fireCustom glazes go on before firing; the finished color depends on body, glaze and kiln together.
6. 06
   MockupFull size samples confirm color and let the maker check that the dies and the extrusion line are behaving before the run.

Glaze

Color is a second firing problem. Architizer’s engineer separates unglazed work, where pigments or oxides fired at about 2,000 degrees Fahrenheit react with the clay to give colors that hold for fifty or a hundred years, from glazed work, where a white or off white body takes a glaze that may be transparent or opaque, high gloss or matte, and layered two or three deep for iridescent effects.⁴ Green Building and Design adds that glaze does little for durability but lifts solar reflectance, and describes a Manhattan condominium whose shading fins took two years to craft in an Italian works, with magnesium pigment added so the slats would match the neighborhood’s existing colors.⁵

From block to panel

The old system was a wall; the new one is a screen. Architect Magazine’s history from trade catalogs records glazed tiles hung on a steel frame to imitate massive masonry a century ago, less costly than carved stone because the pieces were repetitive, and a material that had largely disappeared by mid century.³ Architizer dates the turn to the 1960s, when one German maker began using the clay as a rainscreen cladding product, and credits large curved projects in Europe in the 1990s with showing the geometric range of the material.⁴ The principle those panels rely on, an open jointed outer skin over a drained cavity, has its own entry on the rainscreen idea.

Clips, rails and the cavity

A rainscreen panel never touches mortar. Architizer’s engineer describes clay panels carried on aluminum rails outboard of the insulation, their lapped joints turning water away from the gap behind, with neither grout nor sealant anywhere in the assembly, which is why installation can proceed in any weather and maintenance stays low.⁴ The clips are where the engineering concentrates. On the Bond Street job the panels weighed about 150 pounds each, and the fabricator says that larger, more sculptural pieces often force a modification of standard clip details or a one off attachment; full size mockups served to confirm color and to settle the clips, and to prove the dies and the extrusion line before production.² Green Building and Design notes that because nothing binds the tiles, a damaged one can be swapped without disturbing its neighbors.⁵

Figure

Two ways to put clay on a wall

	Rainscreen panels	Terra cotta faced precast
How it hangs	Panels clipped to aluminum rails outside the insulation	Clay veneer bonded to large precast concrete units
Joints	Open and lapped, with no grout or sealant	Sealed joints between heavy concrete panels
Weight	Masonry appearance without masonry weight	Full precast mass
Energy	Better envelope performance, with insulation outboard	Weaker unless built as a sandwich panel
Upfront cost	Higher	Typically lower
Later cost	Little to maintain	Joints to maintain for decades

Fins, baguettes and screens

The hollow extrusion also makes a sunshade. Architizer describes ceramic pipes of square, round or oblong section used as lightweight brise soleil, and Green Building and Design traces the lineage from stacked breeze blocks to slats and louvers that cut heat gain while letting air through.⁵ On the Upper West Side condominium the same magazine describes, a louvered terra cotta screen shades windows with four panes of glass as part of a Passive House design, so the ceramic is doing thermal work rather than decoration.⁵

Prototypes

Since 2016 the material has had a research bench. The University at Buffalo’s report on the second Architectural Ceramic Assemblies Workshop describes a program launched by Boston Valley with the university’s architecture school, its robotics research group and a ceramics college, in which teams of practitioners and students built prototypes such as a ceramic facade that collects heat and pipes it to an interior ceramic radiator, post tensioned panels combined into larger assemblies, and ribboned rainscreen panels meant to support evaporative cooling.⁸ Architectural Record’s report on the eighth workshop records a rainscreen prototype that used parabolic strengthening to cut typical panel weight by about 60 percent and experimented with industrial slag as a recycled ingredient, a stairwell of terra cotta on a post tensioned spine, and a unitized terra cotta curtain wall seeded with moss; one participant hoped future sessions would study how the metal hardware meets the ceramic so that tolerances between the two can be managed.¹

Why the old anchors failed

The modern system is also an answer to a failure. Building Design + Construction’s account of a Times Square restoration describes a 1912 tower whose white glazed blocks were glazed on the visible face only and fired once, so they took on water and expanded with internal pressures the article puts in the hundreds to thousands of psi, cracking the units and stressing the mortar, while the black iron straps that held them rusted; most of the joints had failed and the building was in danger of losing its skin.⁶ Repairs pinned and epoxied the sound units and replaced the rest with coated cast stone and glass fiber reinforced concrete.⁶ The extruded panel on a stainless or aluminum clip, drained and ventilated behind, is designed so that none of that sequence can start; the practice of repairing the older walls is the business of restoring older walls.

Figure

One Noho rainscreen, in numbers

typical panel length

36 in

weight of one scalloped panel, which drove custom clip detailing

150 lb

shrinkage from extrusion to finished size that the dies allow for

7%

the year, by the fabricator's account, when the first terra cotta rainscreen job came to the United States

2000

What the panel is asked to do

The specification now reads like a promise. Architizer’s engineer puts the life of a rainscreen panel at a hundred years with little maintenance, a power wash every decade or so, and color that does not change for decades, against fiber cement facades that fade.⁴ Green Building and Design credits the material’s thermal mass with buffering outdoor temperature swings and notes that it can be recycled or ground into road base at the end of its life.⁵ Tonality’s survey of ceramic facades makes the general case, from a pyramid shaped Manhattan apartment block whose panel configurations follow its angled geometry to curved museum skins that needed custom forming and careful provision for water and thermal expansion.¹⁰ Whether a given panel, clip and cavity keep those promises is settled the same way as any other skin, on a laboratory mockup and, in New York, on the inspector’s rope every five years.