Masonry Preservation: Terra Cotta

In the early part of the 20th century, glazed terra cotta was the architectural industry’s “cure all” material. Today, however, the repair and replacement of terra cotta building elements presents extremely complex restoration issues. Deterioration of terra cotta creates a cause-and-effect breakdown of entire structural systems, with the failure of the glazed terra cotta units themselves as well as the deterioration of mortar, metal anchors, and masonry backfill.

Another problem is that glazed architectural terra cotta was historically regarded as a waterproof building material, which we now know to be a misconception. In fact, serious water-related failure became evident even in the early life of many terra cotta structures built in the late 1800s and early 1900s.

No one terra cotta deterioration scenario is ever identical to any other, owing to an infinite number of variables, including original construction and installation, amount of component parts, ongoing (and often ineffective) repairs, and an array of deterioration causes. Terra cotta restoration projects involve one or more of the following restoration approaches: 

Terra Cotta Replacement 

True terra cotta replacement is always advisable, but not always possible due to high costs and lengthy lead times. Extra design and construction time is also required due to the expansion of in-kind terra cotta when matching existing mold sizes. If time and budget permits, MPS will secure in-kind terra cotta which is as close a match as possible to previously used materials.

Replacement with Substitute Materials

If a replacement material is deemed appropriate, MPS will take great care to ensure that a material is chosen which does not impair the integrity of the building in question.

  • Stone may be used to replace damaged terra cotta. Stone’s durability makes it highly suitable, although its increase in weight may sometimes be a concern.
  • Fiberglass is often used when elaborate ornamentation needs to be duplicated. Drawbacks include color compatibility, fire code compliance, and poor aging.
  • Glass Fiber Reinforced Concrete (GFRC) is very similar in nature to fiberglass. GFRC is lightweight and can be used on a large scale; color compatibility and poor aging are drawbacks.
  • Precast concrete is ideal for the replication of detail. Precast concrete is cost-effective and can be produced in a time-efficient fashion.

When replacing glazed architectural terra cotta, MPS completely removes all original deteriorated material. Half bricks or similar cosmetic replacement techniques are never utilized by MPS.

When possible and where applicable, terra cotta replacement units are anchored in a manner similar to the original.

Re-anchoring damaged terra cotta is an extremely difficult task. The complexity of the interlocking system of masonry units, backfill, and metal anchoring system prohibits the removal of deteriorated terra cotta without destroying it.

Structural Stabilization

Deterioration of the structural components supporting terra cotta is probably the most difficult form of facade deterioration to locate and diagnose. It can also cause the biggest types of failure, often undermining the structural integrity of large sections of facade.

Structural terra cotta failures can develop due to water penetration, stresses from expansion and contraction, and fabrication defects. To successfully combat the effects of terra cotta deterioration, MPS utilizes the following structural stabilization methods as appropriate (following thorough testing and analysis):

  • Repointing: Repointing of terra cotta which is severely deteriorated is one of MPS’s most useful terra cotta restoration techniques. Repointing is always carried out with a mortar that has a compressive strength lower than the adjacent masonry unit.
  • Glaze Spalling Repair: Glaze spalling is another common source of water-based terra cotta deterioration. It is important to seal affected areas in order to prevent further water entry. Recoating is not a permanent solution, but does prevent the entry of more water.
  • Minor Material Spalling Repair: Minor material spalling is treated in a manner similar to glaze spalling.
  • Major Spalling Repair: Terra cotta which has spalled severely and lost most of its material and structural integrity needs to be replaced. Replacement methods are listed above.
  • Repair of Structural Damage: Structural cracking, holes, or sign anchors should be permanently sealed. Holes and static cracks can be pointed or patched with appropriate proprietary patching material. Active cracks should be filled with elastomeric sealant.