Architectural Scagliola: Characteristics, Uses and Problems

This standard includes general information on the characteristics and common uses of architectural scagliola and identifies typical problems associated with this material along with common causes of its deterioration.

Introduction

Characteristics of Scagliola:

• Modern scagliola was used by Italian craftsmen in The Renaissance (Guido Sassi and Enrico Hugford in Lombardy in the 16th century are associated with this). Its use spread across Europe.
• Pigmented plaster, designed to imitate marble and other precious stones, was used much earlier - common on Egyptian tomb walls and has been found also in Greek, Roman, and Asian structures.
• Commonly referred to as “scag” in the trades
• Traditionally, scagliola was made from a calcium sulfate composition (gypsum, animal glue and natural mineral earth colors), finely ground and mixed with water
• In the United States, scagliola was also made from calcium sulfate. However, Keenes Cement was most commonly used for making scagliola, because this material had slow-setting properties and, therefore, didn’t require the retarder component
• Different formulas for scagliola are appropriate - one type may be better than another for a particular situation; an experienced scagliolist should be able to select the most appropriate mixture of materials

Typical Uses

Typical historical uses for scagliola include:

• Covered Egyptian tomb walls
• During the 16th century, used in a marquetry design for altars, tabletops, etc.
• Architectural potential not fully realized until the 17th and 18th centuries, when the craft was imported to Great Britain, Austria and Germany and used in Baroque churches
• Architectural uses for scagliola in the churches included columns, altar pieces and ethereal clouds
• In Europe, scagliola was common in churches and palaces
• In the United States, scagliola was most commonly used in public buildings, state capitols, railway stations, theaters, and other similar architecturally significant public and private buildings.
• Marezzo was also commonly used in the United States as a less expensive, less elaborate alternative to scagliola

Natural or Inherent Problems

• Cracks: Often caused by differential movement between sections. See 09200-13-R for guidance on repairing cracks.
• Delamination: Typically a flaw in the manufacture of the scagliola and can be as subtle as the placement of the burlap reinforcement, the type and gauge of plaster used for the backing, temperature fluctuations and moisture. See 09200-06-R for guidance on consolidating delaminated scagliola.
• Warped or bowed panels: May be caused by exposure to moisture, or by the natural tendency for these panels to contract.

Vandalism or Human-Induced Problems

• Dirt: Accumulation of surface dirt can result from lack of routine cleaning and maintenance. See 09200-09-R for guidance on removing stains and efflorescence.
• Staining: Can result from the presence of water on or behind the surface and can cause internal metal components to oxidize and produce metallic staining. See 09200-09-R for guidance on removing stains and efflorescence.
• Finish Failure: This may include surface abrasion, small nicks, scratches, and discoloration (yellowing) of the finish over time. See 09200-07-R for guidance on finishing and polishing.
• Efflorescence:Can result from the presence of excessive amounts of water, causing salts from adjacent masonry or within the material to migrate to the surface. See “Removing Stains And Efflorescence From Architectural Scagliola” for guidance on removing stains and efflorescence.
• Fading: Inappropriate use of chemicals for cleaning can lead to color fading.
• Bubbles or surface irregularity: Typically occurs when the retarder component of the scagliola mixture is too strong or too weak, causing inappropriate drying of the color coating and backing.
• Other problems included missing or broken pieces, open joints, loose sections, improper repairs or maintenance, and inappropriate finishes.