3.5.6 Joint Filler. An important feature in the determination of the joint sealant is the selection of the joint filler. The joint filler, or backing rod, performs three functions: 3.5.6.1 Controls both the depth and shape of the sealant. 3.5.6.2 Provides support for the caulk- ing sealant when it is being compressed during tooling. 3.5.6.3 Acts as a bond breaker for the sealant to prevent three sided adhesion. (Three-sided adhesion can result in fail- ure of the sealant.) 3.5.7 Waterproof sealant is applied in joints that have backing rods inserted. The backing rods can be porous (open cell), or nonporous (closed cell), and are typically made of polyethylene or polystyrene rope. 3.5.8 Consult the Sealant, Waterproofing, and Restoration Institute guidelines for further infor- mation on proper joint sealant design, selection, and installation. 3.6 Expansion Joints 3.6.1 Design and Location. Expansion and/or movement joints are essen- tial for the success of stone installa- tions. Various methods require prop- er design and location of expansion joints as shown in “Method EJ171,” from the Tile Council of North America Installation Handbook. [Ed. note: TCNA Handbook for Ceramic, Glass and Stone Tile Installation] Because of the limit- less conditions and structural systems in which stone can be installed, the Specifying Authority shall show loca- tions and details of expansion joints on project drawings. 3.6.2 Final Design. It is not the intent of this manual to make control and expan- sion joint recommendations for a spe- cific project. The Architect must specify control and expansion joints and show location and details on drawings. 3.6.3 Sealants. Where so speci- fied, joints shall be pointed with the sealant(s) referred to in this section, after first installing the specified back- up material and applying a primer if required, all in strict accordance with the printed instructions of the Sealant Manufacturer. 3.6.4 All sealants shall be tooled to ensure maximum adhesion to the con- tact surfaces. 3.6.5 Expansion joint sealants include silicone, urethane, and polysulfide. Generally, urethane sealants are rec- ommended for horizontal stone sur- faces because of their resistance to abrasion and penetration. 3.6.6 Silicone sealants may be used in expansion joints on both exterior and interior vertical stone surfaces. Some one part, mildew-resistant silicone sealants are formulated with fungicide for seal- ing interior joints in showers and around tubs, sinks, and plumbing fixtures. 3.6.7 Sealants should comply with ASTM C920. 3.7 Substrate Limitations 3.7.1 Moisture Penetration. The per- formance of a properly installed stone installation is dependent upon the durability and dimensional stability of the substrate to which it is bonded. The user is cautioned that certain substrate materials used in wet areas may be subject to deterioration from moisture penetration. 3.7.1.1 Wet Areas. “Wet areas” are stone surfaces that are either soaked, saturated, or subjected to moisture or liquids (usually water), e.g., gang show- ers, tub enclosures, showers, laundries, STONE –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 84 TileLetter | May 2018