Type N or S mortar for use with adhered masonry veneer must conform to which ASTM Standard?

The correct answer is ASTM C270, which outlines the specifications for mortar for unit masonry. This standard specifically details the requirements for various types of mortar, including those intended for use with adhered masonry veneer. It covers the materials, proportions, and properties of the mortar, ensuring that it meets the necessary performance criteria for adhesion, strength, and durability in construction applications.

Understanding ASTM C270 is crucial for contractors because it helps ensure that the mortar used in projects with adhered masonry veneer will provide reliable bonding and structural integrity. This adherence to standards is vital for long-term performance, especially in varying environmental conditions that masonry may encounter.

The other standards listed serve different purposes: ASTM C150 relates to Portland cement, ASTM C260 covers air-entraining admixtures for concrete, and ASTM C404 deals with masonry cement. Although all of these standards are important in their respective areas, they do not specifically address the requirements for the mortar used with adhered masonry veneer like ASTM C270 does.