Masonry joints

If a solidly-filled collar joint is specified in a multi-wythe wall consisting of a 4-inch nominal outer wythe of brick and a 4-inch inner wythe of CMU, what should the collar joint width ideally be?
A. 1/2" - 3/4", B. 3/4" - 1"
C. 1" - 1 1/2", D. 1 1/2" - 2"

D. is the best answer. Although MSJC permits 1 inch collar joints, they should be wide enough to allow a high-slump grout to fill the void, around mortar extrusions in the cavity.
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