The installation of metal lath serves as a crucial step in preparing surfaces for stucco, plaster, or other exterior/interior finishes. Proper installation ensures adhesion, structural integrity, and resistance to cracking. This article details the procedures and considerations for installing metal lath, based on available documentation. It covers preparation, fastening techniques, overlapping requirements, and mortar application procedures.
Preparation and Safety
Before commencing installation, certain preparatory steps are necessary. Metal lath edges are sharp, therefore, the use of gloves is recommended when cutting and handling the material. Cutting can be accomplished using either scissors or a saw. A moisture proof barrier should be installed prior to lath application to prevent wood decay. When installing the moisture barrier, seams must overlap by a minimum of 2 inches to maintain a waterproof seal.
Lath Orientation and Installation Direction
LathNet, a type of metal lath, is installed with the mesh drainage mat positioned against the structural wall, and the metal lath facing outward. Installation should begin at the lower left corner of the wall and proceed horizontally from left to right, and vertically from bottom to top. The longer side of the lath should run horizontally. It is important to install lath perpendicular to framing members.
Overlapping and Joint Staggering
Where sections of LathNet meet, a minimum overlap of 1 inch is required. New sections should overlap existing sections in a shingle-like fashion, ensuring the drainage mesh of the new section butts against the drainage mesh of the installed section. Maintaining a continuous drainage plane behind the lath is critical, meaning no gaps should exist between the edges of the drainage mesh. All vertical joints should be staggered to enhance structural integrity.
Fastening Methods and Spacing
Metal lath requires secure fastening to the substrate. Galvanized nails can be used to attach the lath to the wall. Along the edges of the lath, nails should be spaced every 6 inches. For the middle section of the lath, a grid pattern with nails spaced every 12 inches is recommended. Alternatively, lath can be fastened using ties or staples at 9 inches on center.
Expansion Joints
To mitigate cracking, expansion joints are necessary. These joints should be included at least every 18 feet, or wherever walls meet.
Mortar Application
After the metal lath is securely fastened, a layer of mortar is applied. A 1/4-inch thick layer of mortar should be spread evenly over all areas covered with metal lath using a trowel. The mortar should be allowed to dry for approximately 30 minutes. Following the initial drying period, the mortar surface should be scraped with a metal rake, creating horizontal and vertical scratches. These scratches enhance adhesion for subsequent mortar layers. The mortar should then be allowed to dry for a further 48 hours before proceeding with further finishing work.
Seam Overlap
When continuing the installation of metal lath, each new piece should overlap all seams by 4 inches. This ensures a secure and continuous surface for the subsequent application of stucco or plaster.