The next time you’re in a century-old building, tilt your head up for a moment and have a look at the ceiling. It’s probably made of plaster on wood lath. The surface of the plaster may be plain-face or ornately embellished with decorative paint. It may strike you as beautiful or mundane. Either way, what may appear to be just another ceiling is actually a brilliantly conceived and counter-intuitive piece of mechanical engineering, a shining example of craftsmanship, and an important part of our architectural heritage.
Plaster on wood lath was the dominant fabric of choice for ceilings and walls in buildings constructed in North America during the 19th century. While fairly strong and durable, these ceilings and walls are not immune to the ravages of time. Year after year, for decade upon decade, they experience myriad stresses caused by structural overloading, building micro-movements, installation of mechanical systems, moisture vapor transmission and water infiltration.