Masonry Magazine August 1988 Page. 14
Terra Cotta Primer
continued from page 13
it will serve reliably for decades. Unfortunately, during their 50 to 100 years of service, the facades of many terra cotta buildings have suffered a succession of indignities that have permitted excess water moisture to penetrate to, and be trapped within, the body of the terra cotta blocks. This condition is the primary cause of damage and deterioration to terra cotta.
The moisture present in terra cotta will naturally expand and contract in the freeze/thaw cycle. When this moisture is present in excess amounts, the expansion and contraction will eventually result in disintegration and failure.
Typically, the disintegration process is initially visible as cracks in the body of the unit. If the unit is glazed, these cracks will extend through the glaze into the body. As the process accelerates, the glaze may spall and detach itself in large, blister-like flakes, in the process exposing the terra cotta to additional moisture penetration. The moisture penetration may cause the terra cotta tile body to expand, putting surrounding units under sufficient pressure to cause them to crack and eventually fail in turn.
Terra cotta is normally attached to a building via a system of metal anchors. Excess moisture retained within the tile body may cause the metal anchors to corrode. As they corrode, they will expand, cracking the tile body and causing it to heave or jack. The corrosion may also eventually result in a failure of the anchors and loss of the terra cotta unit.
Virtually all terra cotta failures in older buildings can be traced to conditions that have encouraged the cycle of moisture-related deterioration to begin and accelerate. These conditions include everything from problems arising from initial design and installation techniques to ill-advised cleaning or repair procedures and inappropriate alterations.
Damage commonly occurs where moisture-shedding systems (gutters, flashings, downspouts, etc.) have failed or been blocked and when the terra cotta skin and body have been compromised, permitting moisture to penetrate. Sandblasting, cleaning with harsh acids, and bolting signs or other materials over the terra cotta during remodeling will all reduce its ability to resist water absorption.
Cracking of terra cotta units, often the result of unrelieved stresses caused by improper design and installation techniques, is a major source of water penetration. Prior to the mid-1920s, standard building practices called for the terra cotta units' metal anchoring system to be firmly attached to the masonry backup wall. This resulted in a rigid, immobile wall in which no provision was made for the relief of stresses caused by normal building and material movement. These stresses could be very severe in multi-story, steel frame buildings whose whole facades were clad in terra cotta. They were relieved through patterns of continuous cracking that exposed the terra cotta to water penetration. The problem is visible today in terra cotta installations plagued with vertical cracks, bulges in piers, spalls at joints and even falling units.
Building techniques were developed during the 1920s that eliminated the problem, but the procedures were not always followed. Stress-induced cracks can occur on buildings of any vintage, and measures must be taken to repair or replace the damaged units and relieve the sources of stress.
Damage Assessment
Accurately assessing the condition of a building's terra cotta components will normally require that the architect or building owner call in a qualified engineer or terra cotta consultant. In certain cases the consultant may be a masonry contractor with extensive experience working with terra cotta. In other cases, the consultant may be a representative of the manufacturer, who will call upon the masonry contractor's expertise to assist in assessing the condition of the terra cotta and determining a remedial course of action.
Terra cotta deterioration is not always easy to detect. The pieces may literally be ready to pop off, yet appear to be entirely sound. Or there may be apparently insignificant continued on page 28
Extremely intricate designs executed in terra cotta will sometimes fail, particularly in freeze thaw climates where water intrusion is a problem. Caulking and similar attempts at repair that do not solve the underlying problem are short-term solutions at best.
Terra cotta pieces that have failed completely may represent a hazard and should be replaced. To replace this piece, the manufacturer would require a photo or isometric sketch and supporting dimensional information.
Where terra cotta failures are widespread, a consultant may be called for to determine the exact cause of failure and recommend a program of repair, replacement and continuing maintenance.