Deterioration of metal anchoring: Deteriorated anchoring systems
are perhaps the most difficult form of glazed architectural terra-cotta
deterioration to locate or diagnose. Often, the damage must be
severe and irreparable before it is noticed on even the most intense
"prima facie" examination. Water which enters the glazed
architectural terra-cotta system can rust the anchoring system
and substantially weaken or completely disintegrate those elements.
Where water has been permitted to enter the system, some deterioration
has more than likely taken place. Partial deterioration results
in staining and material spalling. Total deterioration and the
lack of any anchoring system may result in the loosening of the
units themselves, threatening the architectural or structural
integrity of the building. Recently, falling glazed architectural
terra-cotta units have become a serious safety concern to many
building owners and municipal governments. Early detection
of failing anchoring systems is exceedingly difficult.
Deterioration of mortar and other adjacent materials: Deteriorated
mortar has always been a key to the survival or failure of any
masonry system. This is particularly true with glazed architectural
terra-cotta. In recognition of the fragile nature of the system,
the need for insuring a relatively dry internal system is important.
Sound mortar is the "first line" of defense in terra-cotta
systems. It is a maintenance "must." Deteriorated mortar joints
are a singularly culpable source of water and, therefore, of deterioration.
Mortar deterioration may result from improper original craftsmanship
or air--and waterborne--pollution. More often, however, lack of
ongoing maintenance is mainly responsible. Deteriorated mortar
should not be overlooked as a major source of glazed architectural
terra-cotta failure.
The deterioration of materials adjoining the glazed architectural
terra-cotta (flashing, capping, roofing, caulking around windows
and doors) bears significant responsibility in its deterioration.
When these adjoining materials fail, largely as a result of lack
of maintenance, water-related deterioration results. For instance,
it is not uncommon to find wholesale terra-cotta spalling in close
proximity to a window or doorway where the caulking has deteriorated.
 The damage shown here is the result of direct live load on a mid-rise building. The steel frame has settled and shifted the weight onto the exterior terra-cotta cladding, resulting in rupturing of the material. Photo: NPS files. |
Stress-related deterioration: Stress-related deterioration of glazed
architectural terra-cotta frequently occurs in high rise buildings.
The evolution of stress relieving details (flexible joints, shelf
angles, etc.) occurred late in the development of American building
construction. Consequently, most early continuously clad High
Rise buildings (c.1900-1920s) had little or no provisions for
normal material and building movement in their original design.
The development of large stress-related cracks or wholesale material
deterioration is often caused by unaccommodated building-frame
shortening under load, thermal expansion and contraction of the
facade and moisture expansion of the glazed architectural terra-cotta
units themselves. Cracks running through many units
or stories or large areas of material deterioration often indicate
stress-related problems. This sort of deterioration, in turn, permits
significant water entry into the terra-cotta system.
Inappropriate repairs: Inappropriate repairs result because using
new terra-cotta for replacement of deteriorated or missing glazed
architectural terra-cotta has generally been impractical. Repairs,
therefore, have traditionally been made in brick or cementitious
build ups of numerous materials such as stucco or fiberglass.
Some materials are appropriate temporary or permanent replacements,
while others are not. (These issues are discussed at a later point
in this report.) However, improper anchoring or bonding of the
repair work or visual incompatibility of repairs have themselves,
with the passage of time, become rehabilitation problems: replacement
brick that is pulling free, cement stucco that is cracking and
spalling, or a cement or bituminous repairs that are not visually
compatible with the original material.
Alteration damage: Alteration damage has occurred as a result
of the installation of such building additions as signs, screens,
marquees or bird proofing. These installations often necessitated
the boring of holes or cutting of the glazed architectural terra-cotta
to anchor these additions to the building frame beneath. As the
anchoring or caulking deteriorated, or as these elements were
removed in subsequent renovation work, these holes have become
significant sources of water-related damage to the glazed architectural
terra-cotta system.
"The Preservation of Historic Glazed Architectural Terra-Cotta" an Historic Preservation Brief
