Conserving a Terra-Cotta Cornice

A treatment report by Conservation Solutions, Inc., on a terra-cotta cornice adorning the Capitol Building in San Juan, Puerto Rico, shows the potentially catastrophic effects of corrosion in a marine environment, and offers some innovative solutions to the problem.
 

by Joseph Sembrat, Head Conservator and President of Conservation Solutions, Inc.

Conservation Solutions, Inc., was contracted by the government of Puerto Rico to assist Pablo Quinones of OPQ & Associates in the investigation of the main terra-cotta cornice at the base of the dome of San Juan's Capitol Building.

CSI subcontracted the services of Martin Weaver, President of Martin Weaver and Associates International Conservation Consultants (MWAICC), who performed investigative work and partial disassenbly of a 6-ft section of the cornice. This was done in order to prevent the collapse of this section of the cornice, determine the cause and nature of the failure, better understand the materials and techniques used in its construction, and provide the architect with various design solutions, cost estimates, and assistance with the writing of specifications.

The Capitol Building of Puerto Rico was inaugurated on February 11, 1929, as the seat of the Legislative Branch of the Puerto Rican Government. A vast marble staircase faces Ponce de Leon Avenue and gives access to the building to the south. Eight Corinthian columns rise at both main entrances and seven imposing doors give access to its interior at the north and south. At the center of the structure there is a rotunda which extends upwards to the three floors of the building, and in the center of the first floor there is a display case which has the original Constitution of Puerto Rico permanently on display. The cornice adorns the base of the dome which rises at the center of the building on an octagonal drum.

To help understand the condition of both the terra-cotta anchoring system and the concrete substructure that supports it, and to assist the clients in their portico-restoration project, CSI conducted an on-site investigation of the terra-cotta cornice and concrete substructure from scaffolding. CSI and Martin Weaver performed written and photographic documentation of the work and provided field drawings to OPQ & Associates.

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A worker is seen here cutting the mortar joints between the terra-cotta blocks in preparation for the disassembly of the cornice.

Puerto Rico's Capitol Building, or "El Capitolio", in San Juan, was completed and inaugurated in 1929. A major port city, San Juan faces the Atlantic Ocean to the north. This marine environment was a major factor in the dangerous corrosion of the anchoring system of the buildings terra-cotta cornice.

The poor condition of the terra-cotta cornice is evident in this view. The separation of the terra-cotta units is due to not only the failure of the anchoring system, but also the expansion of the corroded material.

Once the cornice had been partially disassembled, the materials and techniques used in its construction could be easily identified. Note the clinker concrete, or "cinderconcrete", between the terra-cotta blocks and the brick backup material, and the severe deterioration of the steel supports. CSI recommended that all new steelwork be AISI Type 316 stainless steel, a non-corroding type, which is essential in this chloride-rich marine environment.