Letter to the Editor
I was pleased to see the article on Manufactured Stone Veneer (August 2010). The Masonry Veneer Manufacturers Association (MVMA) was formed to advance the industry and develop consensus guidelines for the installation of adhered masonry veneer. Manufactured Stone Veneers have become one of the more preferred exterior claddings as designers seek ways to improve appearance and performance.
The MVMA helped introduce code requirements for adhered masonry veneers into the International Building (IBC) and Residential (IRC) Codes. The 2012 IRC and IBC will contain specific provisions that they be installed in accordance with the manufacturers approved installation instructions. Additionally, the newly expanded MVMA publication “Installation Guide for Adhered Concrete Masonry Veneer” provides consensus-based guidance for material selection, project preparation, and installation techniques. On behalf of the MVMA, I would like to respond to some issues raised in the article.
While the quality of the accompanying photographs makes it difficult to ascertain, it appears the installations shown were not consistent with the MVMA guidelines. Both Fig. 4 and 5 appear to show adhered stone less than two inches from the adjacent grade, and Fig. 5 seems to show visible lath material. MVMA guidelines recommend a minimum clearance from grade and full embedment of the lath within the scratch coat.
The performance of any mortar, whether for brick, CMU or adhered veneer applications, relies on correct preparation and installation methods. Proper mixing, including consideration of jobsite environmental conditions, helps to ensure that the mortars are of proper consistency and will perform as designed.
The author suggests that Type N and S mortars “do not…achieve the code prescribed shear bond strength…” Not only are these mortars referenced in the MVMA guidelines, but many manufacturers have qualified products for installation with Type N or S mortars in their ICC-ES Evaluation Reports. ICC-ES reports (and the model codes) mandate that installation be in accordance with the manufacturers published instructions.
The author indicates that use of their thin-set masonry veneer installation system “is a solution to all of the problems associated with typical…installations.” Designers should keep in mind, however, that the codes require that the use of any alternative systems such as thin-set mortars be approved and specified by the stone manufacturer. The MVMA formed a project task group, which includes thin-set manufacturers, to evaluate the use of alternate mortar materials. While this collaboration may yield some additional guidance in future editions of the MVMA guidelines, the recommendation remains Type N and S mortars at this time.
Manufactured Stone Veneer is a popular cladding choice that provides elegant and attractive design options, durability and long-term performance. Most important to ensure a successful project are proper materials selection, project planning and preparation, and adherence to the manufacturer’s installation instructions.
To download the MVMA Installation Guide free of charge, visit www.masonryveneer.org/pdf/MVMAManualDesign_web.pdf.