Traditional Masonry Archives — Restoration Case Study

The Ximenez-Fatio House Museum, located in St. Augustine, Fla.

by Patty Miller and Mark Rabinowitz
The Ximenez-Fatio House Museum, located in St. Augustine, Fla., dates to 1798, the Second Spanish Colonial Period. Distinctly Spanish in design, it was built as a two-story masonry structure with a two-story ell addition. Initially a residence, it became lodging for travelers as early as the 1820s and served this purpose well into the 20th century.

Long recognized as one of the most significant early buildings in Florida, this National Historic Landmark was acquired in 1939 by The National Society of the Colonial Dames of America and converted to a house museum. The Colonial Williamsburg Foundation and the National Park Service provided early advice and interpretive direction.

Joseph K. Oppermann, Architect, PA, was hired in 2004 to join historian William Seale in coordinating the first comprehensive restoration effort. Conservation Solutions Inc. was contracted in 2005 to perform analysis of historic masonry materials and provide recommendations for conservation and repair. A beneficiary of a series of state and federal grants, including a Save America’s Treasures Grant, the restoration of the Ximenez-Fatio House Museum began in August 2006. CSI provided site supervision throughout the exterior restoration process. Latitudes NE Florida, a general contractor in St. Augustine, was the primary masonry contractor.

Materials and conditions

The Ximenez-Fatio House is built of coquina stone, a soft shelly limestone that is extremely porous due to a lack of cementing calcite filling the voids between the shells. Although not an ideal building material, coquina was a locally available stone quarried nearby on Anastasia Island, and it was used to build significant structures in St. Augustine, such as the Castillo de San Marcos. The historic materials investigation confirmed that a lime-putty and sand mixture was used as a mortar between stones. The house’s exterior was originally faced with several applications of a lime-putty render and finished with a lime wash.

Over the last 50 years, portland-cement stucco and multiple paint coatings had been applied over the exterior lime render or as a replacement for it, reducing the rate of water-vapor transmission. Water entering the walls of the building began affecting interior wall surfaces, causing damage to interior finishes and deterioration to the stone structure. Results from compression testing of coquina stone samples and water-vapor transmission testing of original lime render samples, portland cement stucco samples and traditional lime-based materials provided the facts needed to make recommendations for repair. Natural hydraulic lime mixed 1-to-2.5 with sand proved to be the closest to the original lime render in terms of water-vapor permeability, appearance and strength. Natural hydraulic lime 3.5 was preferred over cementitious blends for its workability, self-healing characteristics, and salt resistance in a marine environment.

Treatment

The goal of the treatment was to restore equilibrium to the masonry walls by removing all nonoriginal materials that prevented the proper rate of water-vapor transmission and replacing them with new lime render and a traditional lime-wash finish. Treatment began with the selective removal of paint coatings using hydrogen-peroxide-based paint strippers. With paint removed, the white lime-putty renders and gray-to-brown portland-cement-based repairs were readily distinguished, and conditions could be thoroughly assessed.

Portland cement repairs varied from localized infill around window and door openings to skim-coating of entire walls. Although a significant amount of the original lime render still existed, it had been vigorously and deeply scored to accept a skim coat of portland cement that was nearly ubiquitous. The skim coat was hard and thin (1/8-inch to 3/16-inch thick) and poorly bonded to the substrate. It was removed by hand using chisels and scrapers.

The areas of surviving lime render were sounded to determine whether the bond to the coquina substrate had failed. Unfortunately, on walls that were heavily scored, the bond between render and coquina was too damaged to preserve. Tests were performed to evaluate the potential of re-adhering lime renders to the coquina using lime-based grout mixtures. Unfortunately, the open matrix of the stone prevented containment of the grouts, and tests were mostly unsuccessful at re-adhering broad areas of the lime render to the coquina.

Thick, dense portland cement repairs that had adhered directly to the coquina could not be removed without some breakage and loss to the stone. Damage to the coquina was reduced by first scoring the stucco with a 4-inch right-angle grinder into a 4-inch by 4-inch crosshatch pattern with a depth just through the repair layer. Each scored section was then chipped free of the coquina.

Prior to full-scale application of the new lime render, repair mockups were installed using the recommended mixture of 3.5 natural hydraulic lime. As the masons were not familiar with the mixing, application and finishing techniques of natural hydraulic lime, Chuck Spitznagel, technical representative for Cathedral Stone Products Inc., performed on-site training for the masonry contractors.

During the mockup phase, conservators were concerned with the friable condition of much of the freshly exposed coquina. As a means of consolidating the coquina stone, Spitznagel recommended a low-viscosity 1-to-1 mixture of 3.5 natural hydraulic lime and sand be applied to all exposed coquina prior to the application of the scratch coat. Although the material was initially specified to be mixed with only enough water for brush application, the masons altered the application process by adding a little more water and applying the consolidation coat to the coquina using a vertical feed hopper and spray nozzle attached to an air compressor. The consolidation coat was sprayed over a dust-free, damp coquina surface and into cracks and voids as a thin coat in less than half the time needed for brush application. The result was a solid, stable stone surface.

The lime render was a 1-to-2.5 mixture of 3.5 natural hydraulic lime and sand, typically applied as two layers, a scratch coat and a finish coat. Deep voids in the coquina were filled with the same mixture and packed in lifts until the surface was brought flush with the surrounding stone.

The lime render was mixed to a trowel consistency and let stand a few hours to allow the lime to reach a workable consistency. Walls were dampened just prior to application. The scratch coat was applied 3/8-inch to 1/2-inch thick with a steel trowel. After the layer was thumbprint-hard, it was combed to produce the keyed surface required for the finish coat. The scratch coat was protected from drying out too rapidly by occasional misting and protection from direct sunlight. A minimum 3 to 5 days of cure time was recommended before the finish coat was applied.

The finish coat was applied with a steel trowel at approximately 1/4-inch thick. The finish coat was protected from drying out too rapidly by occasional misting during a cure period of seven days and protection from direct sun. For all areas of original lime render that were preserved, a sponge float was used with a thin slurry of lime and sand (mixed roughly 1-to-1) to help fill cracks and small holes or losses in the early render. The final surface appearance of the finish coat can be described as smooth, but not perfectly flat. The finish coat was lightly textured with a stiff bristle brush where new work butts up against preserved original lime render surfaces to eliminate abrupt surface dissimilarities.

A traditional lime wash of 3.5 natural hydraulic lime in water (with no other additives) was applied to all preserved and new exterior renders. The lime wash was applied in three or more successive thin washes using a brush or roller.

The exterior restoration of the Ximenez-Fatio House Museum was completed in December 2007. Interior investigations and restoration are expected to be completed in 2008. Conscientious efforts by the project team permitted the museum to remain open throughout the restoration.
 
Patty Miller, AIC Professional Associate, is conservator at Conservation Solutions Inc. Mark Rabinowitz, AIC Fellow, is vice president of Conservation Solutions Inc. This project was supported by The National Society for the Colonial Dames of America, Florida and National organizations, a Save America’s Treasures grant from the National Park Service, and the Florida Trust for Historic Preservation.

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