What Is Lath and Plaster?

If you’re unfamiliar with lath and plaster, you’re not alone: These outmoded wall construction materials have more or less been completely replaced by the drywall you come into contact with every day. But it would be unfair to dismiss lath out of hand just because it’s an older technique. In fact, if you have the time and resources to install it properly, there are many points in its favor when compared to modern plasterboard.

What is lath?

The lath-and-plaster construction method is a way of creating walls and ceilings out of plaster or stucco by spreading the material over a wood or metal frame (which are the laths) and allowing it to dry. As the wet plaster works its way through the frame, it accumulates on the opposite side, creating plaster keys that hold it in place as it dries.

While the use of stucco for sculpture and building dates back to centuries, the modern formulation and usage of stucco as the primary component of exterior walls only took hold in the 20th century. For exteriors, stucco is typically spread over metal lath (for example, sheets of wire mesh) in at least three layers.

Lath and plaster walls for interiors date back to the 1700s and were widely used until the early-middle of the twentieth century, when their dominance was supplanted by the drywall method (i.e. hanging dried gypsum plaster) most commonly used today. Historically, narrow strips of wood—each a wood lath—were nailed to the frame of the building perpendicular to the wall studs. (Today, metal laths are considered a superior surface for plaster application since a metal lath doesn’t retain moisture like a wooden lath might.) Plaster is then spread over the laths in three distinct coats: the scratch coat, the brown coat and the finish coat.

The advantages of using lath

While using strips of wood laths as building tools is a bit old-fashioned, the lath-and-plaster method definitely has its upsides:

  • Soundproofing and insulation. Compared to drywall, lath and plaster are better insulators, both for sound and for heat. Surprisingly, despite advances in construction technology, many historic buildings are therefore warmer and quieter than modern ones.
  • Fire resistance. In another win for lath and plaster, it’s also generally better than drywall at stemming the spread of fire within a building.
  • Moisture prevention. Using lath for interior walls is also a good choice if moisture is of concern. Lath and plaster walls tend to retain less moisture than plasterboard—especially if you opt for metal over wood lath. 

The downsides of using lath

Of course, there are reasons why drywall is more prevalent today than lath and plaster, and here are a few of the most relevant ones:

  • Time and expense. There’s no getting around the fact that lath and plaster requires more skill and time to install well. Plus, the entire process will cost more than hanging drywall.
  • Difficult repairs. One of the benefits of drywall is how easy it is to take down and replace if it’s damaged. Repairing a lath and plaster wall is much more involved, as you have to tear apart the plaster and potentially tear down the lath, and calls for some skilled labor.
  • Messy demolition. If your lath and plaster walls ever need to be torn out completely, they can create quite a mess since the plaster keys hold the plaster to the wall and don’t come out easily.

Final thoughts

Ultimately, if you’re on a budget or a strict schedule, it probably makes more sense to opt for drywall. But it’s worth having some knowledge of lath and plaster, if only to have some frame of reference if you are working on an old house and discover these anachronistic wooden planks in the walls.

MT Copeland offers video-based online classes that give you a foundation in construction fundamentals with real-world applications, like house framing. Classes include professionally produced videos taught by practicing craftspeople, and supplementary downloads like quizzes, blueprints, and other materials to help you master the skills.

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