By Rick Garagliano
When installing Adhered Concrete Masonry Veneer, the issue of Expansion Joints and Control Joints must be taken into consideration.
First, we must understand the purpose of a joint and difference between an Expansion Joint and a Control Joint. In either case, the purpose of the Joint is to accommodate relative movement of the large, homogenous areas. Expansion and Control Joints provide for the unavoidable movement in a wall that will occur. These designed splits provide a location for the inevitable cracks to form such that they will be less noticeable. After all, cementitious materials are subject to dimensional change caused by thermal changes. In addition to thermal changes, shifting and settling effects can cause movement in the vertical surfaces/walls.
An Expansion Joint is a split or joint that is designed into the structure and extends through the entire width of the wall. Great examples are the joints that form when two tilt-up panels are butted together. In this case, the joint extends completely through the wall. A Control Joint is a separation that is designed into the outer layer only of the wall such as the façade layer. Control Joints are required by code for stucco coatings so that the location of the inevitable cracks is controlled, hence the name “Control Joints”. The code and the designer say “crack here and not anywhere”. Since much of the code requirements for Adhered Concrete Masonry Veneer (ACMV) were initially based on codes for stucco, the Control Joint issue would seem to apply to ACMV. However, recently, a study was commissioned that investigated the need for Control Joints when installing ACMV. The study and report (published on the MVMA website-masonryveneer.org) maintains that when it comes to thermally induced movement, stucco and ACMV do not behave alike. Stucco is a monolithic, vertical panel whereas an ACMV wall is a vertical array of individual stones. Whether grouted or not, the stone wall contains a control joint between every stone. If thermal or mechanical movement is induced, the stone won’t crack but the grout joint of dry joint would “absorb” the movement. Of course, stucco will show the crack if movement occurs. In short, Control Joints are NOT needed for ACMV.
Although Control Joints are not needed for ACMV, Expansion Joints are designed into the job by architects and are needed for the building, not the facade selection. Do not install stone across Expansion joints such that they bridge the Expansion Joint (even if the joint is filled flush to the surface). Eventually, there will be movement at this joint (as designed) and any stones which bridge the joint will crack. The best solution is to terminate stone at each site of the joint, thereby leaving the joint open and uncovered. Sometimes, the stone is installed across the joint and a saw is used to cut the stone on each side of the joint. This method provides a straight, clean cut on each side of the joint. Otherwise, the stones are cut and installed individually along each side of the joint.