water-resistant, dense, uniformly col- ored material. There are two types: white and gray. Damp curing is advan- tageous for both wall and floor types. 3.2.2 Sand-Portland Cement Grout (“Sanded Grout”) 3.2.2.1 Sand-portland cement grout is an on the job mixture of one of the following proportions: one part portland cement to one part clean, fine-graded sand (ASTM C144) used for joints up to 1/8” wide; 1:2 for joints up to 1/2” wide; and 1:3 for joints over 1/2” wide. Up to 1/5 part lime may be added. Damp curing is necessary. Sand-portland cement grout should be applied with caution over softer variet- ies of stone with honed or polished finishes because it may scratch the stone surface. 3.2.3 Polymer Modified Portland Cement Grout (ANSI A118.7) 3.2.3.1 Polymer modified portland cement grout is a mixture of any of the preceding grouts with polymer admixtures. The common polymer types are latex and acrylic. This grout is suitable for all installations subject to ordinary use and for most commercial installations. The use of polymer additives in portland cement grout increases the flexibility of the grout and reduces the permeability. Consult the grout and polymer manufacturers for specific instructions. It is less absorptive than regular cement grout. 3.2.4 Colored Grouts 3.2.4.1 Many manufacturers offer grouting materials in colors. Architects and Designers find them pleasing for aesthetic reasons. Since some stones are more porous than others, test to determine the stability of the relation- ship between the colored joint filler and the stone before proceeding. Make certain pigments contained in the col- ored grout do not stain the stone. 3.3 Sand. Sand should comply with ASTM C144. 3.4 Water. Mixing water must be pota- ble quality. 3.5 Stone Sealants, Backing Rods, and Caulking 3.5.1 Building sealants are normally covered as a separate section in project specifications, and in most trade areas the installation of sealants is not in the trade jurisdiction of Marble Mechanics and Stonemasons. Grouting is almost always in the stone specification. 3.5.2 Silicone Sealants. Some grades of silicone sealants are not recommended by their manufacturers for applica- tion on high calcite content materi- als. Consult the Sealant Manufacturer’s technical recommendation before applying a given sealant to calcite materials. 3.5.3 Severe service areas (patios, decks, traffic surfaces) should be caulked with materials having sufficient abrasion resistance. Consult Sealant Manufacturer’s technical recommenda- tions for sealants in these areas. 3.5.4 Oil based organic sealants should not be used in conjunction with natural stone products because they may stain the stone. 3.5.5 Sealing the Face of the Stone. Nothing in this section is intended to imply that actual sealing of the faces of the stones is a recommended practice. If any sealer coating is specified for any natural stone material, advice should be sought in detail from qualified Stone Suppliers or Installers (See Ch. 3, pg. 3-5, section 5.10). STONE –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 82 TileLetter | May 2018