Old exterior red-wood lath sheathing.
Bulging stucco is a serious indicator of trapped moisture, structural movement, or improper installation, often requiring immediate professional repair to prevent rot, mold, and structural failure. Water intrusion behind the stucco causes underlying wood to expand and the plaster to separate, creating bubbles, ripples, or, in severe cases, causing the stucco to fall off in sheets.
Old wood lath was used for stucco many years ago.
Byrkit lath (sometimes spelled Bryker or Byrket) is a specialized type of old, tongue-and-groove, wood-lath sheathing used in home construction, primarily from the late 19th to the early 20th century. It acted as both the exterior structural sheathing (“boxing”) and the lath for exterior stucco, eliminating the need for separate sheathing and lath boards, thus saving on labor and materials.
Key Characteristics and Features
Design: It consists of wood boards, often redwood), featuring a tongue-and-groove (T&G) profile. Unlike standard siding, Byrkit lath has specially designed “keys”—grooves, notches, or gaps—cut into the face of the boards.
Purpose: These keys allowed stucco to penetrate and lock into the wood, creating a very strong, durable, and sturdy wall system.
Usage: It was frequently used as a base for exterior stucco in the early 1900s. It was often installed over the framing before stucco was applied, sometimes over a layer of felt paper.
Performance: While it can be very durable, it requires proper maintenance. If the stucco is not maintained (e.g., painted regularly), water can penetrate the wood, causing it to swell and ruin the stucco.
Commonly Associated Terms
“Patent Board”: Due to its proprietary, specialized design, it was sometimes referred to as a “patent board”.
Redwood: Often made from durable species like redwood for rot resistance, especially when used on exterior applications.
Stucco Substrate: It is known for creating, when in good condition, a very sturdy wall that results in few cracks compared to traditional lath.
When remodeling, this material is often found in homes built before 1930 and is sometimes encountered when removing old stucco for renovations.
Material: It was made from durable lumber species, with redwood and cedar being common choices, prized for their natural resistance to moisture and pests. The use of redwood was particularly popular in areas like California due to its local availability and weather resistance.
Design: Unlike traditional lath which consisted of individual, separate strips, Byrkit lath was typically tongue-and-groove or square-edged boards with special grooves or “keys” cut into the face of the wood. These keys allowed the stucco or plaster to push through and “grab” the board, creating a strong mechanical bond, or “keyway”.
Purpose: It was designed as a labor-saving material, combining the structural sheathing (which protects against external elements) and the lath (which provides a base for plaster/stucco) into one product. This reduced the labor and the number of nails needed for installation.
Performance: Homes built with Byrkit lath were often noted for their sturdy construction and lack of wall cracks when the material was properly maintained. A tar paper or similar weather-resistant barrier was typically installed behind the lath on exterior walls.
In summary, Byrkit lath was an innovative, multi-purpose redwood building material popular decades ago for its efficiency and durability in stucco applications.
As promised, in this video, See more methods in the video below.
Remove and repair loose stucco from old wood lath or continuous board lath, or Byrkits patent sheathing.
https://youtu.be/miTVy-XYrl8
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Cheers, kirk Giordano Plastering Inc.
