Rationale

The current requirements in ASTM C1780 for installation includes two methods – Method A (which is back-buttering of the unit) and Method B (which is applying setting bed mortar to the substrate). While these methods are suitable when using conventional mortars, they may not always work for modified mortars. Further, there could be other installation methods for installation that achieve the desired result – full coverage of mortar on the back of the unit and transfer to the substrate. This ballot item proposes to revise this section to make the goal of installation clear, and then list several ways that have been shown to be accomplished. This allows the user to choose the installation method that they prefer, while still including requirements for what they need to accomplish. This ballot item also adds a note to inform the user that the prescriptive design option in TMS 402/602-22 does not allow the use of conventional mortars in these prescriptive designs.