Northern California framing in wood or steel is almost universally restrained construction. This means that each change in finish material and every wall length are tied together. In restrained construction, the interior wallboard, framing, exterior underlayment, and lath are continuous, creating a monolithic building designed to resist movement. In this type of construction control joints are installed on top of the lath, with the lath installed continuously as a component of restrained construction process. This is one construction process.
The other construction process is unrestrained construction, where walls are defined in 10’ to 14’ panels characterized by double studs, a felt insert between the studs and breaks in the interior wallboard, breaks in the exterior underlayment, and breaks in the lath, each break allowing for independent movement of each panel. In this type of construction, a two piece expansion joint should be installed at each panel change.
Confusion occurs when the lath details, lath codes and ASTM C-1063 do not differentiate between the two types of construction or the different characteristics of two types control and expansion joints. The Plastering Industry also uses the two terms interchangeably, adding to the confusion.
Control Joints control the application of the plaster panels (thickness and cold joint concerns). Control joints in restrained construction need blocking. Attachment into the substrate is not acceptable.
Expansion joints define plastered panels when installed over differing materials, or in areas of potentially significant movement. Expansion joints in unrestrained construction need the same type of blocking as the interior wallboard framing.