STUCCO PROJECT BACKGROUND INFORMATION



The National Park Service (NPS) is in the process of a project to preserve and protect the North Wall of Old San Juan, between Forts El Morro and San Cristóbal. This will assist to counter the long-standing effects of the wind, water, and vegetation which are causing significant damage to the historic masonry walls.

Working with the U.S. Army Corps of Engineers, the NPS recently completed a ten-year, 45 million dollar effort to stabilize some of the historic walls from destructive wave action and erosion which had undermined major portions of the walls and fortifications. We now have turned our attention to treating the serious problem of the surface deterioration of the North Wall. The walls are generally constructed of soft sandstone rubble and mortar with a stuccoed exterior layer. Much of the stucco coating is worn or eroded. If this state of deterioration if not arrested, continued deterioration will expose the interior rubble fill and eventually could lead to a structural failure of the wall itself.

Skilled masons are first cleaning sections of the wall, patching large voids with a first layer of stucco, and applying a thin outer layer of stucco. The stucco application techniques are very similar to those employed by the Spanish over the 350 years they maintained the walls. The soft stucco being used is also very similar to the mixture used by the Spanish, consisting primarily of sand, lime and water. The NPS arrived at this approach to preservation of the walls after considerable research and testing.

A local television station recently reported that the NPS is plastering the historic walls with portland cement identical to the gray type used in new house construction. This is not correct. As stated above, the stucco being applied is similar to the historic stucco applied by the Spanish. A small measured amount of white portland cement, in a ratio of 1 to 10, is being added to the stucco to help the stucco bond to the walls. Masons in many parts of the world throughout history have covered stone and brick walls with stucco to protect the walls from the harmful effects of weather. Stucco also protects walls from water saturation. Stucco is intended to be worn away by contact with wind and rain and becomes a sacrificial layer which will wear and erode off over time and will someday need to be replaced.

Concerns have been raised that the stucco project has changed the appearance of the sections of the North Wall recently completed. Experience has shown that this "newer" look will be short-lived and that a more "aged" appearance will soon return. Stucco testing previously conducted at San Juan National Historic Site (San Juan NHS) indicate that the new look does not last long on the walls. The harsh tropical weather guarantees a rapid weathering that soon creates an aged appearance.

In 1986, the NPS commissioned a massive study of the walls and fortifications to determine the causes of the deterioration and to recommend the best method to preserve, protect and repair the walls. The study took five years and costs nearly one-half million dollars. This was followed by three years of field testing to determine the appropriate preservation treatment. This study was clearly the largest historic research project that the NPS has ever done in the Southeast U.S. and Caribbean. The research team assembled for the study included personnel from San Juan NHS, and other NPS experts from the North Atlantic Historic Preservation Center in Boston (now the Cultural Resources Center in Lowell, MA., the Southeast Regional Office in Atlanta and the NPS headquarters in Washington, D.C. Private consultants were also employed, led by the Columbia University's Center for Preservation Research, in New York City.

The study team began their research and field work in 1986 with almost every wall and surface being documented and photographed. The study dealt with every tunnel, bastion, and sentry box. Hundreds of documents were researched, some going back to the 1500's. The research team had translated archaic and complex military terms and extracted and analyzed hundreds of representative mortar and paint samples. The study resulted in a three-volume historic structural report, published in 1991, titled: "The Fortifications of San Juan National Historic Site."

During the study, NPS researchers found a 1839 report by Pedro Tomás de Córdoba in which he reported the successful conclusion of a nine-year effort to clean and reface with white/beige stucco the totality of the surfaces. Much of this stucco still survives, but much of it is eroded, streaked, and stained.

Earlier archival documents indicate that the Spanish carried out substantial stucco and plaster work in 1832, 1808, 1783, and 1771. One of the surprises revealed in the Historic Structures Report was that:
"...during the approximately 350 years of fortification construction within the Spanish period , there was no significant change of construction techniques or materials."

Constructing and maintaining the fortresses and city walls was a continuous task over the centuries. Analysis of surviving stucco indicates that the Spaniards achieved a remarkable consistency with a traditional maintenance program of repointing and re-stuccoing when necessary. Thanks to their work, the form and character of these historic monuments survive today.

The fortifications of San Juan have evolved over more than four centuries and are managed today by the NPS as part of a 75-acre historic site. The primary historic features of the San Juan NHS are three forts and approximately 2.7 miles of massive stone walls which virtually enclose the old city. Included here are two of the world's most impressive fortifications: El Morro, which guarded the western approach, and provided ocean defense, and controlled access to the bay of San Juan; and San Cristóbal, which guarded the eastern approach and provided land defense. A third, smaller fortification was El Cañuelo, located across the bay from Old San Juan, constructed to provide cross fire over the bay and to prevent enemy landings at the western side of the harbor. Research determined that during the approximately 350 years of fortification and wall construction and maintenance, only in the mid-to-late twentieth century were changes in techniques or materials made. The research required that nearly 600 samples of mortar, stucco, and plaster be taken to assist in dating the various elements that comprise the fortifications. Under microscopic examination a variety of sands, limes, and aggregates, including crushed brick and sea shells were found.

The research team determined that various forms of mortars are found throughout the fortifications. The term "mortars" is used in the study to generally describe these materials. Mortar is broken down specifically as bedding mortar, plaster, hormigón, and stucco. A bedding mortar is used to bind the rubble, generally consisting of the sandstone or brick substrate within the walls. Hormigón as used historically, is a poured mix with pulverized brick that was used for roofs, terrepleins, and similar areas that needed to be more impermeable to water penetration. The mix that was applied with a trowel to coat the wall substrate was referred to as plaster, if it was an interior wall, or stucco, if it was used on an exterior wall. The composition, the manner of fabrication, the tooling of finishes, and the method used to impart the color are all significant factors that have to be known or determined in order to replicate, patch, or replace any section of walls covered with stucco.

Historically, stucco was applied to masonry structures as a means of protecting them and their porous substrate from the erosive effects of weathering. The stucco received the brunt of the weathering and was intended to deteriorate over time; periodic re-stuccoing kept this sacrificial surface layer intact, in a similar way to paint being re-applied to protect and maintain masonry or wooden structures.

In 1993, the NPS felt that the most significant recommendations found in the Historic Structures Report should be presented to the public and the professional preservation community. Field testing for stucco replacement had just been completed and NPS wanted to include the opinion of as many experts in the preservation field as possible. The Third International Symposium for Historic Preservation in the Caribbean (held May 9-11, 1994) highlighted the issue of re-stuccoing the fortification walls. The presentations included lectures on the issue of stuccoing, an on-site visit to review field testing, stucco color samples, and first hand laboratory test results. In attendance were architects, masons, engineers, landscape architects, archaeologists, historians, and other professional preservationists, many from the Puerto Rico State Historic Preservation Office, the Institute of Puerto Rican Culture, Universities, and from private practice.

Starting in the summer of 1995, an NPS preservation team made up of experienced Puerto Rican masons set up scaffolds and started the arduous task of coating the outer north wall at Castillo San Cristóbal with a beige stucco. This north facing wall was chosen because it shows the most serious deterioration problems. The north wall faces the powerful sea, the continuous trade winds, and experiences more rapid plant growth than other areas which receive the more powerful impact of the direct tropical sun. That summer and the following one, the masons resurfaced about 10% of the north wall. The process they used was reexamined prior to the start of this year's work and the method was simplified to increase productivity in the limited work season.

First, small plants and their roots are carefully removed from the cracks and crevices of the wall. Second the wall is cleaned with a low pressure water spray. And finally, the soft lime mortar is applied following the field-adjusted recommendations.

Long ago the Spanish masons made their mortars and stucco mixes from lime and sand: lime by burning crushed limestone in a special fire-pit to reduce it to a whitish powder substance, and the sand taken either from the beach or from inland sand pits. Microscopic analysis of mortar, plaster and stucco samples taken from the fortifications shows evidence that both kinds of sand were used. Beach sand would have to be washed thoroughly to remove salt before it could be useful in construction. Pit sands had the advantage that they were not contaminated with salt, but often were "dirty" and full of impurities. After field testing, the NPS decided to use a combination of clean beach and pit sand to obtain the appropriate historic color and the texture needed to stucco the walls.

The monumental fortified walls of Old San Juan had to be built with a thicker base to support the needed height, and few people can tell by looking at the outer surfaces of the city walls that the walls are not made of solid stone. Military engineers from the Spanish period built the walls as huge, hollow boxes. Outside portions of the walls are laid of stone blocks and sandstone laid with mortar; the interior volume of the walls are filled with "mamposteria" ( rubble work and earth fill). Broken bricks, chunks of sandstone, limestone, and other construction debris were bound together with a wet slurry of mortar inside the hand-laid stone walls. The rubble work and earth fill is very porous and rain water will eventually infiltrate through he walls from above. If enough water is trapped inside the walls the weight of the mamposteria and fill could eventually slump down and push out the walls. The pressure force of trapped water inside a wall is surprisingly heavy a gallon of water weighs over 8 pounds. Over 55 inches of rain typically fall in San Juan each year. That means that just over the central core of Castillo San Cristóbal approximately 12 million pounds of water could penetrate and exert pressure on the walls of the fort. When that sacrificial layer of stucco is missing, there is a tremendous potential for water to infiltrate the surface of the walls and cause irreparable damage. This highlights the importance of the stucco project for the future preservation of the entire fortifications and city walls of San Juan. The forts and walls presently do not appear the way they have always looked and their appearance in 1995 is quite different from 1960, 1930, or even 1900. Since the agents of deterioration are constantly attacking the walls, they are always in a stage of change. A look at historic photographs from the early 20th century, and to those taken by the Historic American Building Survey (HABS) in the 1960s, when compared to the most recent photographs and measurements in the mid-1980's reveal that deterioration is clearly affecting the surfaces. These changes may not be immediately apparent to those who live or work here and see them often. The stucco application will change the present appearance of the fortifications. However, historic buildings made of wood are regularly painted in many parts of the world to protect and preserve them, and almost no one objects to the "new appearance" when a fresh coat of paint is applied. Stucco and plaster for masonry buildings should be viewed the same way as paint on a wood building. Both paint and stucco are sacrificial layers that protect against deterioration of the underlying structural materials.

Some may object to any change made to the appearance of a historic building . They fear that visitors to San Juan will not see the forts and city walls as "ancient" once they are resurfaced. Others have suggested that visitors will think these are reproductions and not the authentic historic walls. Other critics believe that the deterioration of the walls is part of the natural aging process and they tolerate the idea that eventually the walls and fortifications themselves will become ruins, in a similar way, to the present appearance of the Roman Coliseum.

The notion of letting the historic fortifications of San Juan -- a World Heritage Site -- fall into a state of abandonment is totally irresponsible and unacceptable to the National Park Service. The NPS has a moral obligation to receive, preserve, and transfer to future generations the cultural patrimony as intact as possible. It is true that the fortifications of San Juan no longer function as an active military site, but when the San Juan NHS was established, the forts and walls were turned in 1961, and the NPS by mandate, was directed to protect the historic resources in a state as near to the original as possible for this, and future, generations to visit and enjoy.

In summary, the NPS has invested over ten years of efforts to determine the best way to protect the fortifications of Old San Juan. This effort started with years of academic study and professional analysis followed by more years of practical on-site testing by experienced preservation teams. The process described is in accordance with the standards of the Secretary of the Interior and consistent with applicable articles contained in the 1964 Venice Charter prepared by the International Council of Monuments and Sites (ICOMOS).

Re-stuccoing the walls should be viewed as a continuation of the historic Spanish traditions beginning shortly after construction and continuing into the early 20th century. The re-stucco process described here is without a doubt a sympathetic treatment that preserves the integrity of this impressive fortification system for the future.