Plaster

Lore & Background

Plaster is a building material primarily used for cladding interior walls, ceilings, and pool interiors, as well as for molding and casting decorative elements. In English, "plaster" typically refers to interior applications, while "render" denotes exterior use, and "stucco" describes a different mixture for external wall cladding. The most common types contain gypsum, lime, or cement, all functioning similarly: manufactured as a dry powder, mixed with water to form a stiff paste just before application. The reaction with water releases heat through crystallization, causing the hydrated plaster to harden. While wet, plaster can be easily worked and molded by hand or with tools, and cured pieces can be joined together. It is preferred for aesthetic finishing rather than load-bearing; thick decorative applications may require a hidden supporting framework. Beyond building, plaster has medical uses in orthopedic casts for broken bones, and in dentistry for creating dental models from impressions. In art, lime plaster serves as the traditional base for fresco painting, where pigments are applied to a thin wet top layer and fuse with it, making the painting part of the plaster itself. Historically, plaster was also used for large figurative reliefs, though few survive. Plaster first appeared as a building and decorative material in the Middle East over 5,000 years ago. In Egypt, gypsum was burned in open fires, crushed, and mixed with water to create mortar for pyramid blocks and smooth wall facings. In Jericho, plaster was used to decorate human skulls to appear lifelike. The Romans later spread plaster-working techniques across Europe.

Reader's Guide

Plaster's significance lies in its versatility and long history as a building and decorative material. It has been used for interior wall cladding, moulding, and casting for millennia, with evidence from ancient Egypt and Jericho. The material's ability to be worked while wet and hardened through crystallization made it essential for both structural and aesthetic purposes, though it is preferable for finishing rather than load-bearing. Its legacy includes medical orthopedic casts, dental models, and fresco painting, where pigments fuse with wet lime plaster. Clay plaster, one of the earliest types, was widely used in colonial America and German settlements like Old Economy Village, but fell out of favor with the rise of lime and gypsum plasters. Despite its decline, clay plaster survives in historic buildings, offering a hand-made alternative to modern finishes.

Did You Know?

• Plaster was used in ancient Egypt as mortar between pyramid blocks and for smooth wall facings.
• In Jericho, human skulls were decorated with plaster and painted to appear lifelike.
• The name 'plaster of Paris' comes from gypsum deposits at Montmartre in Paris.
• Clay plaster was used in the American colonies and at Old Economy Village in Pennsylvania.