Historical Architectural Terra Cotta Replacement with GFRC (Glass Fiber Reinforced Concrete) or GFRP (Glass Fiberglass Reinforced Polymer)

Terra Cotta Replacement Table of Contents

What is Architectural Terra Cotta?	Replacement Choices	Selecting the Supplier for Terra Cotta Replacement
	GFRC (Glass Fiber Reinforced Concrete) as a Terra Cotta Replacement FRP (fiberglass reinforced polymer) as a terra cotta replacement	What to look for What about quality?
How the process works	Architectural Elements	Technical Data
Survey Shop drawings Models and molds Casting and finishing Installation	Parapet Caps and Copings Balustrade and parapet rail Columns and column capitals Cornice Gargoyles and figures	Specifications for Architectural Terra Cotta Replacement with GFRC Specifications for Architectural Terra Cotta Replacement with FRP CAD drawings Test data Color options
Additional Reading
US National Park Service Preservation Brief: The Use of Substitute Materials on Historic Building Exteriors US National Park Service Preservation Brief: The Preservation of Historic Glazed Architectural Terra-Cotta

What is Architectural Terra Cotta

Terra Cotta is from the Italian for "baked earth". Terra-cotta elements became popular for architectural elements between the late 1800s through the 1930s. Architects such as Louis Sullivan, Cass Gilbert, and Daniel H. Burnham and others produced several terra-cotta clad masterpieces of American architecture.

To produce architectural terra-cotta, clay was mixed with sand or crushed pottery. The mixture was then packed into molds or carved. Once the terra-cotta had air dried it was fired. Terra-cotta was then glazed. In other words, terra cotta was an enriched molded clay brick. Terra-cotta was usually cast in hollow blocks which were open to the back, like boxes. The terra cotta was molded with internal stiffeners of clay called webbing. The webbing strengthened the load-bearing capacity of the hollow terra-cotta block.

Architectural terra-cotta was generally finished with a glaze. The terra cotta glaze provided color, protected the clay, and imitated different materials such as stone. The terra-cotta glaze had rich color a hard surface. Glazing terra cotta offered virtually unlimited color to the designer.

Today many of these terra-cotta clad buildings have serious deterioration problems. Sources of new glazed architectural terra cotta are limited.

Replacement material choices

Depending on the application, the location and the degree of deterioration, terra cotta will either need to be repaired or replaced. Replacement choices are either FRP (fiberglass) or GFRC (glass fiber reinforced concrete).

NOTES ON REPLACEMENT:

When properly preformed, GFRC or FRP replacements of terra cotta should be virtually indistinguishable from the original material.
When replacing glazed architectural terra-cotta, all of the original deteriorated material should be completely removed. Do not try to replace a half block or part of a piece.
Anchorage should be concealed.
Visual compatibility should be a major consideration when choosing a replacement material.
Re-anchoring deteriorated terra cotta units is practically impossible due to the anchorage method of steel straps, mortar and interlocking courses. If the terra-cotta in question is loose, deteriorated, or its structural integrity is in question, it is best removed and replaced.
Always keep in mind the potential liability of a poorly done job. A piece of terra cotta can become lethal when it falls.

GFRC (glass fiber reinforced concrete) for Terra-Cotta Restoration and Replacement

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For over 25 years, the Stromberg Company has pioneered in the development of GFRC replacement pieces for terra-cotta. The use of Stromberg GFRC as a replacement for architectural terra-cotta offers several advantages

Stromberg GFRC is lightweight and easier to handle than terra cotta
Stromberg GFRC is faster to erect than terra cotta
Stromberg GFRC reduces the loads on the building structure
Stromberg GFRC reproduces fine detail and texture and can be molded in complex shapes
Stromberg GFRC is environmentally friendly
Stromberg GFRC is low maintenance

GFRC (glass fiber reinforced concrete) offers great benefits in replacing glazed architectural terra-cotta.

Benefits of GFRC:

Anchoring provisions are included in casting
Color compatible
Non combustible material, GFRC will not burn
Light weight
Durable and long lasting
Suitable for seismic zones
Fast production times

What is GFRC?: GFRC (glass fiber reinforced concrete) is concrete that uses glass fibers for reinforcement instead of steel. It is typically cast in a thin section of around 1/2" to 3/4". Since the fibers cannot rust like steel, there is no need for a protective concrete cover thickness to prevent rusting. With the thin, hollow construction of GFRC products, they can weigh a fraction of the weight of traditional precast concrete or terra cotta.
How strong is GFRC?: As an engineered material, the properties of GFRC can vary depending upon mix design, glass content and production methods. Glass fiber used in quality GFRC has a higher tensile strength than steel. As a general rule, the higher the fiber content, the higher the strength. A typical GFRC mix with 5% glass fiber has a flexural modulus of elasticity of around 1.5 to 2.9 x 10 6 and compressive strength of 6,000 to 8,000 psi.
How durable is GFRC?: GFRC has been tested both by accelerated aging tests in the laboratory and in real life installations. GFRC can be expected to last as long as pre-cast concrete. In many environments, as when exposed to salt spray or high moisture, the GFRC can be expected to perform better, as there is no steel reinforcement to corrode. Since the surface of GFRC is a Portland concrete, it weathers much as a quality architectural pre-cast concrete would.
How is GFRC attached?: Most GFRC can be divided into two categories: with internal frame and without. GFRC with an internal frame is for larger pieces and panels. The internal frame allows for what would have been multiple pieces of terra-cotta , to be installed in one large unit. GFRC without the internal frame is generally set one piece at a time, much the way terra-cotta would have been. This is useful in cases where not all of the terra-cotta needs to be replaced. How do you make the GFRC (glass fiber reinforced concrete) match the existing terra-cotta elements or match terra-cotta elements that no longer exist? In some cases a historic structure has pieces on it that we can take mold from, to exactly replicate the existing terra-cotta In other cases all that's available our old photographs or drawings of terra-cotta architectural elements that no longer exist. In these instances our sculptors and model makers re-sculpt the piece from the historical images.

FRP (Fiberglass Reinforced Polymer)

FRP Fiberglass Reinforced Polymer replacement is an excellent alternative, particularly when rich and elaborate ornamentation has to be duplicated. Molds are taken from original intact pieces or models are produced from photos and dimensioned drawings. Several pieces can be combined into one large unit.

Benefits of FRP:

Anchoring provisions are included in casting.
Color compatible
Class A fire rated
Light weight
Durable and long lasting
High ratio of strength to weight
Suitable for seismic zones
Faster production times
Resistant to water, acid rain, rot, rust and corrosion

Replacement of architectural terra-cotta with fiberglass offers several advantages. Fiberglass has the ability to duplicate intricate and elaborate ornamentation, fiberglass is lightweight and easier to install a terra-cotta, Stromberg fiberglass is durable and weather resistant is particularly suitable for seismic zones and hurricane areas.

What is FRP?: FRP stands for fiberglass reinforced polymer. Most people are familiar with fiberglass boats, yachts and Corvette bodies. In the last 40 years, fiberglass has proven itself to be strong, durable and waterproof. To produce fiberglass, special polymer resins combine with strands of glass fiber.
How strong is FRP?: FRP is an engineered material and its strength can be designed to meet specific needs. By increasing fiberglass content the strength of the FRP is increased. As a general rule Stromberg FRP for terra-cotta replacement as about 60 times the impact resistance and tensile strength of architectural terra-cotta.
How durable is FRP?: Stromberg FRP (fiberglass) has been used around the world. Fiberglass columns, domes and architectural details from Stromberg have withstood hurricanes, blizzards and earthquakes as well as tropical sun, seawater (even submerged!) and ground contact. FRP does not rot, harbor termites or rust.
What about glazes and colors?: Stromberg has years of experience in replicating terra-cotta glazes in GFRC (glass fiber reinforced concrete) and FRP (Fiberglass). We would be happy to help you with your restoration and preservation project.

Selecting the Supplier for Terra Cotta Replacement or Restoration

So how do you go about selecting the best source for replacement elements for architectural terra cotta?

Experience: With projects around the world and across the USA no one can offer the experience and expertise in historical restoration and replacement that Stromberg can. For 30 years, we have been producing restoration products and with our continuous improvement process we learn with every project. Put our experience to work for you.
Capacity: When schedule is important, you want a company with the capacity to get your project done. No one can offer you more capacity for production. Large jobs are no problem.
Options: We offer a full range of expertise in GFRC, FRP and terra cotta. We can recommend the best material for your project and can help develop the best combination of approaches to meet your needs.
Customer satisfaction: Over 80% of our business is repeat customers. We encourage you to speak with our clients.

Give us a call or email. Let us prove what we can do for you.

Architectural Terra Cotta Services we provide:

Custom CAD drawings and renderings from historical documents
Art molds from existing terra cotta pieces
Custom sculpting and recreation of missing pieces
Site surveys, testing , inventory and consulting
Engineering of terra cotta replacement connection methods and means
Color matching and texture matching of terra cotta glazes
Reproduction of terra cotta in GFRC or FRP
Turn key replacement

What about quality?

Stromberg has worked on some of the nations leading historic landmarks. Stromberg Historic is part of the Stromberg family of companies, with over a quarter century and work on some of America's finest architectural treasures.

Clients and commissions include:

The White House
The Smithsonian
The Pentagon
West Point
Yale
St. Peter's
Palaces, five-star hotels and historical treasures throughout the world

How the Process Works

Terra Cotta Survey

Upon request, a survey is performed of the existing terra cotta. Surveys may include:

Historical Research for documents to determine the original condition of the terra cotta.
Inventory of existing terra cotta installed
Survey of condition of existing terra cotta, sealant condition, flashing, anchorage. Each piece of terra cotta may be sound tested by tapping with a rubber mallet to determine if it is sound.
Survey of missing terra cotta

Shop Drawings

Detailed shop drawings in CAD format are produced that detail each piece of terra cotta, its location, and setting plans. These drawings include sections, connection details, jointing and hoisting. These shop drawings are submitted, along with material samples to the architect for approval.

Models and Molds

Models are created from the drawings and molds produced from those models. If original pieces still exist, then the molds are produced from the original pieces.

Casting and Finishing

The GFRC is cast into the molds and compacted. The GFRC is a mixture of sprayed in cement, fine aggregate, polymers and additives along with glass fibers. The fiberglass reinforced concrete is allowed to harden in the mold, and is then removed and sanded or finished. Framing can be incorporated into the fiberglass cornice if necessary. To match the original terra cotta, the color is determined by cast in pigments and the aggregates, as well as glazes.

Installation

The replacement elements are then installed. A range of stainless steel and other non corroding straps, anchors and attachments are available. The new elements can be designed to be installed one piece at a time, or as multiple elements preassembled and erected in large lengths or panels.

Typical Architectural Terra Cotta Elements and their Replacements

Parapet caps and coping

A typical terra-cotta parapet cap or coping.

Because the limitations of the manufacturing process for terra-cotta, it was not possible to produce large pieces. This required numerous joints which allowed the possibility of water infiltration through the top of the parapet. In replacing this deteriorated parapet cap the three individual terra-cotta units were cast as one single piece of GFRC with "false joints" that were then pointed with mortar.