STONE ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– only to the natural surface, but also the treatments used to make a surface smooth. Application of a coating is sometimes consid- ered a way of addressing smooth- ness; however, coatings have a tendency to chip or flake over time, thus creating their own diffi- cult-to-clean surface. As a result, there is a prohibition on the use of coatings for surfaces subjected to cutting and chopping actions, such as countertops and cutting boards. It is important to note that this prohibition would not neces- sarily apply to all surface treat- ments the natural stone industry might use. Sealers that are buffed off to the point where they only remain to fill surface imperfec- tions are not considered a “coat- ing” for the purposes of NSF standards, and could potentially be used on countertops and cut- ting boards. 6.5 Toxicity. Standard 51 requires that materials meet FDA regu- lations for their intended end use, as specified in the Code of Federal Regulations, Title 21 (21 CFR). Applying Standard 51 tox- icity requirements to the stone is fairly easy. Because natural stone does not fall under the scope of 21 CFR, we simply conduct extraction testing to verify that the material does not contain any regulated heavy metals. When sealers are used, NSF must have verification from the sealant man- ufacturer that it meets 21 CFR. An alternative is that the sealant manufacturer can obtain an NSF certification. Copies of each standard can be obtained online or by fax from the source. 7.0 ASTM SPECIFICATIONS AND STANDARDS 7.1 Material Specifications 7.1.1 ASTM C503, Standard Specification for Marble Dimension Stone (Exterior) 7.1.2 ASTM C568, Standard Specification for Limestone Dimension Stone 7.1.3 ASTM C615, Standard Specification for Granite Dimension Stone 7.1.4 ASTM C616, Standard Specification for Quartz-Based Dimension Stone 7.1.5 ASTM C629, Standard Specification for Slate Dimension Stone 7.1.6 ASTM C1526, Standard Specification for Serpentine Dimension Stone 7.1.7 ASTM C1527, Standard Specification for Travertine Dimension Stone 7.2 Test Standards 7.2.1 ASTM C97, Standard Test Method for Absorption and Bulk Specific Gravity of Dimension Stone 7.2.2 ASTM C99, Standard Test Method for Modulus of Rupture of Dimension Stone 7.2.3 ASTM C120, Standard Test Method of Flexure Testing of Slate 84 TileLetter | July 2019