Is it true that prehydrated tuckpointing mortar has lower bond strength than conventional mortar, which is not prehydrated? If so, is flexural cracking more likely in walls that are tuckpointed?
No, there should be no problem with bond strength or flexural cracking in properly mixed and applied tuckpointing mortar. Properly applied tuckpointing mortar has more complete contact with the masonry units than the original mortar did. This is because the prehydration and compaction (from tooling) reduces the amount of shrinkage. Tuckpointing is done to make walls more watertight. The old mortar is generally deteriorated or contains numerous separations. These conditions contribute to low flexural strength in walls under wind suction loads. Proportion tuckpointing mortars so they're as strong as or weaker than the original mortar. Don't use a higher cement content to increase the bond of the tuckpointing mortar. High cement content mortars shrink more and may separate from the masonry units, increasing water penetration and reducing bond. These mortars also are harder and may cause the unit faces to spall.