Guastavino Shells

Introduction:

Catalan vaulting relies upon layers of thin tiles connected with mortar to span space. Its origin can be traced back to medieval Spain. It was developed and introduced to the United States primarily through the work of Rafael Guastavino and the associated Guastavino Fireproofing Company which was founded in 1889.

In America he found a market for fireproof construction and a superior quality of cement that allowed him to expand upon the possibilities of traditional Catalan masonry. During the 70 years of its existence, the Guastavino company was involved in the construction of over 2000 buildings in America. Guastavino collaborated with some of the century’s most prominent architects, such as McKim Meade & White and Cram Goodhue. Some of his most notable works were the Boston Public Library, Oyster Bar at Grand Central Station, Queensborough Bridge, St. Paul's Chapel, St. John the Divine.

Process:

The basic units of construction under the Guastavino system were the masonry tiles which provided structural support, fireproofing, sound absorption, and aesthetic finish. Standard dimensions for the tiles were 6x10” with an average thickness of 3/4”. The size of the brick was determined in part by the ease with which it could be hand-placed by the masons.

Application of first layer of tile:

Tiles were positioned either by hand or against simple wooden templates. Tiles were laid flat against the curvature of the roof unlike more traditional masonry techniques in which stones or bricks were individually shaped to fit a particular curve. The first layer of tiles were connected with plaster of Paris. Taking advantage of plaster’s quick set-up time, each tile was held in place until it set. In this way a base layer of tiles, usually the bottom structural layer, was established for the section of vault or dome being built.

Application of subsequent layers of tile:

Mortar was then spread over the first layer of tiles. The second layer was added on top of the first, using the same size tiles but in a different pattern so as to cover the joints of the previous layer. Anywhere from three to five layers of tiles were used, according to the loads present. For the dome of St. John the Divine a span of 98 feet was covered with a shell that narrowed from 12” at its base to 3.75” at its crown.

Working from the base to the crown, workers laid out 18” of layered tiles across the circumference of the dome. Standing on their past day’s work, mason laid the next section of tile. Taking advantage of the inherent strength of their materials allowed the Guastavino Company to dispense with expensive scaffolding.

Finish work:

Where the vaults were closer to scrutiny, finish work enhanced the appearance of the Guastavino roofs. Decorative tiles were often added in a herringbone pattern, a pattern that is now associated with Guastavino’s most celebrated spaces. Tiles were applied from the center of the vault or dome and masons worked towards the edges, irregularly cutting only the last few tiles that bordered the walls. Another decorative finish included a raised mortar pointing that emphasized the module of tile used.

Qualities of Guastavino Construction:
Guastavino domes and vaults had several great advantages over other vaulting systems of that era. By integrating the structural system into the skin, Guastavino roofs allowed for an economy of material and formwork. Through advertisements, the Guastavino Company differentiated its domes from contemporaneous steel supported, double shelled domes. By using a standard modular tile, their construction method was adapted to form a variety of spaces.

Understanding the structure of Guastavino constructions:
Prior to the development of steel supports and reinforced concrete, a flat roof of any great span was not possible. Vaults and domes were the alternative. In the 19th century, Guastavino Company tile construction presented the most successful solution to the problem of spanning great distances.

Analogy to the modern concrete shell:

Guastavino vaults and domes behave as monolithic surfaces, ones that function as single units rather than assemblages of parts. Their material composition confirms this in that more than half of the material used in their construction is mortar. Guastavino roofs can be seen then as behaving similarly to concrete shells, with the tiles behaving as aggregate that adds rigidity to the shell.

Utilizing undevelopable surfaces, surfaces that retain their shape under loads, Guastavino benefited from the inherently rigid properties of the dome and saddle shaped curve.

In such complex curves, longitudinal forces resist the compressive weight of the shell along with all live loads bearing upon it. Cohesive bonds in a lateral direction between the mortar and tiles resist the forces that in an arch (a curved surface that lacks such lateral connections) thrust outwards. This even distribution of loads within the surface of the shell does not allow for appreciable deformation from bending. The product is a rigid shell that allows for a span of 400 or 500 times its thickness. When compared to the span to thickness ration of an eggshell, which is 50:1, the strength of cohesively bonded tile and mortar is dramatically shown.

Failure modes:

In spite of the advantages of Guastavino structures, they were not suitable for all conditions and have failed in particular modes:
-Poor workmanship and age in some buildings allowed water to penetrate beyond the surface layer of tiles. The gypsum base of the plaster joints dissolved, and endangered the cohesion between adjacent tiles.
-Because thin shell construction relied upon its rigidity to carry loads, differential settling that occurred in the structure that surrounded and supported it endangered its stability.
-In the special case of the Queensborough Bridge market, excessive vibration from bridge traffic above combined with enlarged rusted metal reinforcements damaged the vaults. The addition of a bituminous layer added for water protection also cut down on the cohesive properties of the vaults.

Conclusion:

Despite the commercial success of the Guastavino system, the development of the concrete shell along with sharply rising labor costs after World War II forced the end of Guastavino’s “cohesive construction” in this country. In developing nations where labor costs are not prohibitive and the reinforcing needed for concrete shells is unavailable masonry based on traditional Catalan techniques is still practiced.

Recently, attention has been refocused on the work of Guastavino for two reasons. First, several recent renovations of Guastavino spaces have brought attention to their unique visual qualities and still inadequately understood structural character. Second, led by the efforts of architectural historian George Collins, the history and influences of Guastavino’s work has been opened for the first time to critical study. Both address the relevance of these American examples of cohesive construction, and the potential for its future use.

guastavino tiled supermarket under Queensboro bridge