Rationale

This ballot is proposing a series of changes to ASTM C1780 to align the requirements of the standard with the 2022 version of TMS 402/602 (Building Code Requirements and Specification for Masonry Structures). The 2022 version of those standards included a significant overhaul of requirements for all veneers (both anchored and adhered). As this version is now referenced in the 2024 International Building Code, it is appropriate to proceed with changes to align C1780. The 2022 TMS 402/602 contains two primary options for design and construction – the prescriptive option and the engineered option. For the prescriptive option, TMS 402/602 provides a detailed set of requirements for materials, substrates, fastening, and more. When those details are followed, additional design is not needed. For the engineered option, there are very few prescriptive requirements, instead requiring engineering of the system, but allowing a much larger range of materials and systems. The changes to ASTM C1780 proposed here are aligning the standard with the prescriptive options. The goal of these changes is that an installation that follows ASTM C1780 will be an installation compliant with the prescriptive option in TMS 402/602-22. Specific changes included in this ballot: • New Section 1.2 that states the standard is intended to cover prescriptive installations per TMS 402/602-22, and mentioning that the engineered design option is available for situations outside of the standard. • New Note 3 – this relocates existing Section 6.1 (before renumbering) regarding reference to the Appendix for information on modifying the shear bond test to evaluate non-standard installations. • New Section 4 on Significance and Use – This section is a required mandatory section per ASTM Form and Style Manual, but the standard never had it before. The language proposed identifies the limitations for the prescriptive design and construction option in TMS 402/602. If any installation does not meet these criteria, they would need to go to the engineered option. The addition of this new section also necessitates renumbering of the standard from that point on. • Updated Section 5.5 on mortar – TMS 402/602 has particular requirements for mortars used in adhered masonry veneers. Most significantly, the setting bed must be a modified mortar meeting ANSI A118.4 or A118.15. Revisions to 5.5 are proposed to make this section clear and also align with the TMS requirements. • Removing installations that require engineered option – there are two substrates currently in C1780 that require an engineered design in the new TMS 402/602. These two substrates – open-stud and existing cured stucco – are proposed to be removed. Note 9 has been added to let users know that these were historically included. • Lath fastening – TMS 402/602 includes tables for fastener size and spacing based on the weight of the veneer, the type of structural backup, and the width of the cavity between the backup and the veneer. A reference to those requirements in addition to ASTM C1063 is added to 7.3.2.2. • Additional cleanup – throughout, minor changes to clean up language and corrections to section references are changed as well. Because of the breadth of the changes, the entire standard is provided below for reference. Changes are limited to those identified in strikeout/underline. NOTE: There is another ballot on ASTM C1780 that is in process. This ballot is making modifications to the unit installation procedures (Section 8.2 shown below) to include provisions for installing units with modified mortars. It is acknowledged that there will need to be coordination between these, but it is expected this will be handled in a subsequent ballot item.