Plaster Base Coat Thickness Over Metal Lath: Getting It Right

Lath and plaster is a building process used to finish mainly interior walls and ceilings. The technique involves nailing narrow strips of wood (laths) horizontally across the wall studs or ceiling joists and then coating them in plaster. The plaster is typically applied in three layers: the scratch coat, the brown coat, and the white coat. The thickness of the plaster base coat over metal lath can vary depending on the application and the desired finish.

In traditional lath and plaster construction, the plaster base coat is often thicker than modern drywall. A typical lath and plaster wall required a minimum of three coats of plaster, resulting in a dense, rock-hard coating nearly 1 inch thick. The thickness of the plaster base coat can vary depending on the number of coats applied and the thickness of each coat.

When using metal lath, it is important to ensure that it is stretched tight and secured properly to the studs or joists. Some sources recommend using a backing material such as craft paper or tar paper to minimise the loss of plaster through the mesh. The thickness of the plaster base coat will also depend on the desired finish and the number of additional coats that will be applied.

In summary, the thickness of the plaster base coat over metal lath can vary depending on the specific application, the desired finish, and the number of coats applied. It is important to consider the overall thickness of the plaster and lath system when determining the appropriate thickness for the base coat.

Metal lath is available in 27-inch by 8-foot sheets

Metal lath is made of hot-dipped galvanized steel, which provides enhanced strength and durability. It resists damage caused by rust, fire, and insects, making it a reliable option for both interior and exterior applications. Its versatility extends to its ability to be easily cut and formed around curved surfaces, ensuring a smooth finish.

When used as a plaster base, metal lath provides a strong reinforcement for the base coat of plaster. The large number of openings in the metal lath allows for better stucco bonding, creating a secure and long-lasting finish. Metal lath is particularly useful for achieving consistent plaster depths, minimizing the appearance of stress cracks.

The standard thickness of a plaster base coat over metal lath is not explicitly stated, but it is important to apply a sufficient amount to ensure proper adhesion and a smooth finish. The thickness may vary depending on the specific project requirements and the number of coats applied.

Overall, metal lath is a versatile and durable option for construction projects, offering ease of use and a high level of durability. Its availability in 27-inch by 8-foot sheets makes it a convenient choice for a variety of applications, providing a strong and reliable base for plasterwork.

The plaster base coat should be about 1/4-inch thick

When applying plaster over metal lath, the base coat should be about a 1/4-inch thick. This is the first of three layers of wet plaster that are applied to the lath. The plaster dries to form a hard, smooth surface that can be finished with primer, paint, or wallpaper.

The process of applying plaster over lath typically involves the following steps:

• The lath, which can be made of wood or metal, is nailed horizontally across the wall studs or ceiling joists.
• Temporary lath guides are placed vertically against the wall, usually at the studs.
• Lime or gypsum plaster is then applied using a wooden board, dragging it upward to force the plaster into the gaps between the lath and leaving a layer on the front about 1/4-inch thick.
• A helper feeds new plaster onto the board as it is applied.
• When the wall is fully covered, the vertical lath guides are removed, and their slots are filled in, leaving a fairly uniform undercoat.
• A second layer of plaster is applied in the same fashion, leaving about 1/2-inch of rough, sandy plaster (called a brown coat).
• A smooth, white finish coat is applied last.

This traditional method of plastering over lath creates a thick, dense layer that provides insulation, fire resistance, and soundproofing. However, it is time-consuming, labour-intensive, and requires skilled labour, making it expensive to install and repair.

The brown coat is the second layer, which is about 1/2-inch thick

The brown coat is the second layer of a three-coat plastering process. It is applied in the same fashion as the first layer, but it is left about 1/2-inch thick. This layer is rough and sandy and is used to further flatten and plumb (make vertical) the walls.

The first layer, or scratch coat, forms the plaster keys and provides basic coverage. The keys are globs of plaster that are pushed out of the backside of the lath. These globs dry and form a myriad of secure grips for the rest of the plaster.

The third and final layer is the white coat, which provides a smooth surface for painting or wallpapering. Sometimes, this final coat is textured.

The final white coat is the smoothest and thinnest layer

The first layer, or scratch coat, forms the plaster keys that provide basic coverage. The scratch coat gets its name from the fact that it is scored to help the next layer adhere to it. The second layer, or brown coat, is used for further flattening and plumbing (making vertical) the walls. The final white coat is then applied, providing a smooth finish.

The three-coat plastering process is time-consuming and labour-intensive, requiring skilled plasterers to ensure the plaster is properly applied and the wall is smooth and level. This traditional process has mostly been replaced by modern drywall, which is faster and less expensive to install. However, lath and plaster construction is still favoured for its superior sound-proofing, insulation, and fire-resistance qualities.

Plastering over metal lath requires skill and is time-consuming

Plastering over metal lath is a highly skilled job and a time-consuming process. It is a traditional building method that has been largely replaced by drywall, which is quicker and easier to install.

Metal lath is a lightweight and easily attachable base for plaster application. It is made from expanded steel and attached to stud planes with staples, nails, or wafer head lath screws. The plaster is then applied, filling the openings in the lath and creating a secure bond. This process is time-consuming and requires a high level of skill to ensure a flat, smooth surface.

The plastering process typically involves three layers: a scratch coat, a brown coat, and a white coat. The scratch coat provides basic coverage and forms the plaster keys, which are globs of plaster that dry and create a secure grip for the rest of the plaster. The brown coat is used for flattening and plumbing the walls, while the white coat provides a smooth surface for painting or wallpapering. Each layer must be allowed to dry before the next one can be applied, which can take several days.

In addition to being time-consuming, plastering over metal lath can also be more expensive than drywall due to the cost of skilled labour. It is a labour-intensive process that requires specialised knowledge and experience. The plaster mix must be carefully prepared, and the application process must be carefully controlled to avoid cracking or other issues.

Overall, plastering over metal lath is a skilled trade that requires time, patience, and a high level of expertise. While it has been largely replaced by drywall, it is still used in some situations, such as the repair of historic buildings or the creation of ornamental shapes.

Frequently asked questions