Terms & Tools: Plaster & Stucco
Mineral components (sand, stone, shell) added to mortar, plaster, or concrete. Aggregates are the strength reinforcement to mixture and it decreases shrinkage. The choice of aggregate for a mortar is directly related to particle size distribution, or the range of small to large and proportions thereof.
When the lime (calcium hydroxide) in mortar or plaster is changed into a carbonate. Occurs when lime reacts with carbon dioxide from the air, releasing water through evaporation and forms calcium carbonate.
In lime plastering or pointing, it is the intimate bonding of calcium hydroxide and water that is achieved through pressure. Failure to get sound cementitious bond between layers of plaster or mortar leads to delamination or two separate unconnected lifts.
A mode of failure where bonded layers of a material separate. Both manmade and natural materials can delaminate. Wood, plaster, paint and even stone can delaminate. Stone delamination, similar to exfoliation, occurs along the natural bedding planes. This kind of deterioration can occur when layers of a stone are laid skyward instead of horizontally, when expansion and contraction occur due to trapped moisture in the stone, by the expansion of rusting metal embedded in the stone, or by weathering caused by harsh conditions.
Shallow grooves running vertically along a surface, most commonly a column or pilaster.
Pieces of stone chips set into pointing at a fairly regular interval. Believed to be a decorative feature but in some cases applied to facilitate stucco application.
An ancient technique where the render is thinned with water to a soupy consistency, scooped up on a curved trowel and thrown against the masonry with considerable force to create a cratered surface.
Also known as a mortarboard. A square board with a handle underneath; used by masons and plasterers to carry mortar or plaster.
A support for plaster. Now commonly constructed of expanded metal mesh, it was originally constructed of wood strips nominally a quarter-inch thick by 1.5" wide and in lengths running perpendicular over several floor joists or wall studs with about a fingertips spacing in bewteen for plastering mortar to wrap around and through to provide a "mechanical key," or hook, around the backside of the lath. There are two kinds of historic lath: riven and circular cut. Prior to the 1830s lath was riven from larger pieces of wood. After the 1830s, lath was cut with the circular saw, a new invention. Very useful for dating buildings or renovations.
A stucco interior or exterior treatment installed with the intention of addressing water problems.
A flattened column, attached to the wall.
To remove, carve wood.
A type of stucco exclusively applied to masonry walls.