The tape and “float” technique is effective for repairing wider cracks in plaster. Sand the patch smooth with fine-grit sandpaper on a sanding block. Allow each layer to dry, then sand lightly before applying the next coat. If a hairline crack has been evident over a period of time and doesn’t move, remove the loose material and fill the crack with a coat or two of joint or spackling compound (or use an elastomeric product like Krack Kote). In other words, a willing beginner can make minimal repairs, and with practice, progress to more challenging projects. Patching cracked walls is a skill that falls somewhere between the trades of plastering and drywall finishing. They can follow structural members in a straight line or run diagonally across the wall surface. Cracks can range from hairline-size to very wide. For a bathroom where the original plaster is long gone or compromised by water damage, for instance, greenboard is an excellent choice.Ĭracks can be caused by foundation settlement, undersized joists, seasonal and humidity changes, and poorly executed repairs. This makes it easier to tailor drywall with specific characteristics to areas where moisture or mold is a problem. Manufacturers offer drywall for diverse uses and settings: there are fire, moisture, or mold resistant varieties, for example, and rock that serves as a base for tile installation. Once the joints are taped and coated with joint compound, drywall is ready to be painted or wallpapered. It can be nailed or screwed to wood or metal studs. Offered in a standard 4′ x 8′ size and thicknesses from ¼” to 5⁄8″, drywall is relatively easy to install over large areas, especially compared to plaster. In the U.S., it began its inevitable march to residential walls and ceilings between 1910 to 1930. It isn’t as old as plaster, but drywall has a surprisingly long history, with early forms dating back to the late 19th century. Known variously as plasterboard, gypsum board, Sheetrock (a trade name), rock, or wallboard, drywall is a uniform panel of gypsum plaster pressed between thick sheets of paper. Old work can be replicated, but that’s another story. 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. 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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