Detailing Architectural Terracotta- Water Leakage

Preventing and Repairing Water Leakage and Damage in Terracotta

Architectural terracotta has been used in a wide range of architectural styles – from the Chicago School to the Beaux Arts style. Some incredible buildings emerged from the late 19th century through the 1930s that used glazed terracotta. However, over time, the natural elements have begun to erode these architectural marvels.

This blog post provides background on terracotta as an architectural material, what water can do to terracotta structures, and how to prevent water leakage in terracotta in order to maintain architectural terracotta.

Understanding Terracotta

Architectural terracotta is made of aged clay that is mixed with sand or other types of clay and then is molded and fired at a high temperature to give it hardness beyond what is possible with brick. When translated from Latin, terracotta means “cooked earth,” and it can vary in color like the Earth from red to brown to even white.

For structures, terracotta was made into blocks that were open at the back and were finished with a glaze to change the color but, on a practical level, help provide a surface that could deal with the elements.  This glaze provided the terracotta with the necessary weathering properties to make it stand the test of time. It was particularly favored for its low maintenance as it did not need to be repainted and could be restored with regular washing. However, like all materials, architectural terracotta does eventually give into elements, including water.

What Water Does to Terracotta

Over time, architectural terracotta does deteriorate most commonly due to water. The water does damage to the terracotta on many levels:

  • Crazing is the formation of tiny cracks in the glaze.
  • Spalling is the partial loss of the masonry material.
  • Glaze spalling are blisters in the glaze where it becomes ruptured.
  • Material spalling is considered the worst type of water damage and can deteriorate it from the both the outside glazing and the internal webbing and porous underside.
  • Deterioration of the metal anchoring can be difficult to locate but does eventually impact the integrity of the architectural terracotta.

Preventing Water Leakage in Terracotta

In order to prevent water leakage in terracotta, it is important to understand how water enters a structure and what conditions are present. There are three key conditions that have to be available for water to penetrate a structure:

  1. There is an opening.
  2. There is water present at that opening.
  3. There is a force that pushes that water through the opening.

To prevent or repair these conditions and help maintain the integrity of terracotta, a number of strategies can be used that fall into these three strategic categories:

  1. Eliminate the opening.
  2. Keep water from going toward an opening.
  3. Neutralize the forces that push the water through that opening.

Each of these three main strategic categories are discussed next, including the types of building assemblies that are appropriate for achieving that strategy and keeping terracotta free of water leakage. Having a partner like TerraGlas can provide a great solution for addressing these types of issues as they have a team of professionals who have experience with these types of water issues and know how to employ the strategies listed below.

The first strategy is to eliminate the opening. This can be challenging because every structure has an opening of some kind. Let’s face it, walls have cracks around windows and doors while a shingled roof leaves openings under each of its shingles. Over time, these openings may become bigger and make water leakage a greater challenge to control. There are three main strategies that have their advantages and disadvantages:

  • Sealant joints: These are used to seal up the openings, but they can fail to adhere to the material if the area is not first cleaned well. Sealants also do wear out over time.
  • Gaskets: These can seal as long as they are sized correctly and are resilient in relation to the external environment. Over time, these can fail as well.

Overall, while these do have their weaknesses, they are ideal to use in the correct way as part of the larger strategy of controlling water leakage for terracotta.

The second strategy is to keep water away from openings by diverting it away from the structure. There are many tactics that can be used, depending on the type of the structure. These tactics include:

  • Wash: This introduces a slope to the surface and helps the water drain away from the structure. The steeper this slope on the architectural terracotta, the faster the water can be moved away from the opening.
  • Overlap: This is where a higher surface is extended over the lower surface in order to move the water along and away without coming into contact with the lower surface where the opening is located. This can be achieved through roof shingles and tiles as well as flashing.
  • Overhang and drip: The overhang on architectural terracotta provides a way for the water to be moved in drops or streams down the wall of a building. The overhang must be created in relation to certain weather issues, such as wind-driven rainfall, in order to ensure the water does drip down and away from any openings.
  • Drain and weep: This is most often an internal system that uses spaces or channels as well as the force of gravity to push the water into weep holes or other types of openings to direct the water outside and away from the architectural terracotta.

The third strategy is to neutralize the forces that push the water toward and through the openings in structures. The forces that are at work include:

  • Gravity: Use a wash or overlap to neutralize gravity
  • Surface tension: Use overhang and drip to neutralize surface tension
  • Capillary action: Use capillary break, labyrinth, rainscreen assembly, and upstand to neutralize capillary action.
  • Momentum: Use capillary break, labyrinth, rainscreen assembly, and upstand to neutralize momentum.
  • Air pressure differentials: Use capillary break, labyrinth, rainscreen assembly, and upstand to neutralize air pressure differentials.

As these findings suggest, multiple tactics are often the best approach as no single tactic has the power to block water.

The tactics not previously explained but listed here as additional strategies include:

  • Capillary (moisture) break: Many exterior building materials are not waterproof and are considered permeable. In this case, moisture breaks are created through the use of weep holes.
  • Labyrinth: Building joints can be created that block any raindrop or snowflake from entering. There are many different types of labyrinths that can be made, depending on the building structure, including those for vertical joints and horizontal joints. While it cannot prevent windblown water or snow, it does assist in the overall three-prong strategy noted here.
  • Rainscreen assembly: One way to assist with blowing rain or snow is the construction of a rainscreen assembly, which prevents water being pushed through due to the force of air pressure differentials. It serves as a continuous air barrier and uses a both a drain and flashing to further prevent water from being forced in due to wind or inclement weather.
  • Unobstructed drainage: Drainage can be poorly designed and still invite paths of water into architectural terracotta. However, with further research that traces the path of the water, a better type of drainage system can be created that does not become obstructed over time but that continues to help achieve this three-pronged strategy. This will take considerable time to understand how water travels and where obstructions may occur, but it will help ensure the longevity and integrity of the architectural terracotta.

These strategies are designed to help extend the beauty of architectural terracotta so that the structural beauty can be enjoyed for years to come. These are fairly simple, yet highly effective, strategies to employ in order to address water leakage in architectural terracotta, making them worthwhile investments of both time and money.

Contact us now at 903.454.0904 or email us at to get started with a trusted, experienced architectural terra cotta materials and products partner.


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