Vertical Installs: Bonding To Last

   With that popularity, there’s a need for instruction on new products and systems to effectively install thinly-cut stones on vertical applications – especially for exterior conditions.
   In addition, stones today are fabricated with a variety of backings that provide added rigidity and stability. Bonding some of these backings can be challenging for installers. However, using the correct installation system can overcome these hurdles and provide a permanent, trouble-free installation.
  
PUTTING IT UP
   There are several types of application methods currently used for the vertical installation of stone. One is the mechanical anchor system, primarily used for large, thick stones where kerfs, pins or dowels can be fabricated into the stone and fastened to the building structure or frame. Structural stone panels are also installed using this method. Though it has been utilized for decades, mechanical anchoring is very labor intensive, slow and costly.
   An application method gaining fast support is the spot-bonding method via high-strength epoxy adhesives. Fast, easy to install and offering tremendous cost savings, high-strength epoxies offer many advantages over the mechanical anchor method.
   With thinner stones, mechanical anchors aren’t even an option; the stone is too thin to fabricate a kerf, or anchor it with pins or dowels. Currently, the main method used for thin stone veneers is the direct adhered method.
   For exterior applications, generally a high strength, two-component, liquid-latex-fortified, Portland-cement-based thin-set mortar is used. A rapid rise in high-strength, polymer-fortified, one-component thin-set mortars is also evident with stone installations today; high-strength epoxies are also on the rise. These mortars and epoxy thin-set mortars can also be used for interior applications of vertical stone.
   Always consult with the manufacturer of the epoxy thin-set mortar for exterior application precautions. Proper thin-set mortar coverage on stone backs is also important for vertical installations.
   Exterior areas exposed to moisture should receive at least 95-percent continuous thin-set mortar coverage. Back buttering stones in these applications will ensure proper bedding and coverage. Be sure to use the appropriate thin-set mortar for the substrate as well; this will ensure a proper bond.
   Exterior applications should only be installed over concrete or masonry-type surfaces. The substrates should be rigid and structurally stable and not susceptible to excessive deflection. Exterior applications will be more demanding due to weather conditions such as freeze/thaw cycling, wind load and thermal expansion. A project engineer should carefully detail the installation system to ensure that all of these factors are considered prior to the installation of the stone.
   Substrates should be properly prepared to receive the waterproofing membrane, stone adhesive or leveling mortar. The substrates should be free of bond-breaking or bond-inhibiting materials, such as sealers, waxes, curing compounds, form release agents, paint, dirt, grease, oils, and laitance (a milky residue on newly poured or troweled concrete).
   If these materials are present on the substrates, they must be completely removed prior to the commencement of the installation. Mechanical abrasion is the best way to remove these contaminants; avoid using chemicals or acids, as they can get into the substrate and will be virtually impossible to eliminate.
  
WATCH THE EXPANSION
   Waterproofing, anti-fracture membranes and high-strength, liquid-latex-fortified, Portland-cement-based leveling mortars can also be beneficial in installation. A waterproofing membrane should always be specified and included in exterior applications; manufacturers of tile- and stone-installation products can provide a complete system for a specific application.
   Also, expansion allowance should always be included in any stone installation. Exterior installations will require wider and more-frequent expansion joint placement, and a project architect/engineer should provide direction on the design, placement and construction of all expansion joints.
   The sealant these joints should also be durable, weather-resistant and able to handle the required movement. Silicones and urethane sealants are usually best for these applications; latex or acrylic caulks are only suitable for interior non-wet areas. Most of the available sealants match the grout or stone colors to blend in with the entire color scheme of the installation.
   Latex-fortified Portland-cement based grouts are usually used for exterior veneers. In some instances an epoxy-based or new-generation cross-linking grout can be used as well. Consult with the grout manufacturer on limitations for exterior applications. Epoxy and cross-linking grouts provide color fastness, and are stain-resistant and easier to maintain – they never need sealing.
   The stone used for the application should also be carefully chosen, as some types may not be suitable for exterior vertical applications or exposure to moisture. Also, some backings supplied with certain stones may have limitations that restrict applications. Make sure that the stone manufacturer or supplier of the stone recommends the stone for your specific application.
   Local building codes can also be consulted for information on size, height and weight limitations for direct-adhered applications.
   Thin stones can be successfully installed in vertical applications in interior and demanding exterior applications. To keep quality on par with increased use, though, the industry needs to use the right high-strength quality installation materials – and know how to use them.
   Arthur Mintie is Technical Services Supervisor for LATICRETE International Inc. in Bethany, Conn.

This article first appeared in the November 2003 print edition of Stone Business. ©2003 Western Business Media Inc.