Ornaments including ceiling medallions are cast in a mold, then applied. Mouldings, however, are run in place, the profile created by pushing a template against wet plaster. This article concerns itself with three-coat plaster, applied to wood or metal lath and troweled smooth. The result is a superior, handmade wall surface that offers surprisingly good insulation and sound-proofing qualities.
Once the brown coat has cured, the top or finish coat goes on, either smooth or in a variety of textured finishes. The Brown CoatĪs the brown coat goes on, the plasterer levels out wall surfaces and creates square and plumb corners. The top surface of this scratch coat is then scored to prepare it to receive the second or brown coat. The plasterer forces the wet mixture thickly through gaps in the lath to form “keys” that harden and lock the coat in place as it cures. Three coats of wet plaster are applied in layers to the lath: the scratch coat, the brown coat, and the finish coat.
Illustration by Rob Leanna based on Kathy Bray What is a 3-Coat Plaster System?Ī traditional multi-coat plaster system begins with a substructure of lath-thin wood slats or metal mesh-that’s attached to the wall framing. Three-coat plaster is a system of multiple layers that work together to form a strong, sound-dampening, fire-resistant wall. About 150 years ago, a new component, gypsum, was added to the sand and lime mixture to enable the plaster to cure more quickly and allow for faster working times. Historically, plaster consists of dry components including sand, lime, and cattle hair (or straw or manure) mixed with water to create a wet, plastic medium that cures and hardens as it dries. More serious repair problems include delamination, bulging walls, and key failure, where plaster has broken loose from its grip on the lath substructure.Īpplied with craft and skill, interior plaster is a near-magical building material for creating and coating walls and ceilings. The most common type of damage to plaster is cracking, progressing from the superficial and easily repaired to deeper and wider cracks that require multiple repair techniques.
#PLASTER SKIM COAT OVER DRYWALL PATCH#
It’s much easier to repair cracks or patch holes with this versatile material than with drywall. In many cases, problems with plaster can be fixed. If sections or entire walls need attention, don’t let the idea of working with old plaster intimidate you. Many houses built before about 1950 retain at least some of their original plaster walls.
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