Many architect’s tuckpointing specifications state that the mortar is to be removed to a depth of 3/4 inch or until sound mortar is reached. The mortar is badly deteriorated in an older elementary school building that we are working on. After removing the outer 3/4 inch, we continued to rake away the mortar, in many cases to the full depth of the brick units. Obviously, when too much of the mortar is raked away, the brick units themselves become unstable.
What would you recommend in cases like this? Should we just tuckpoint to a depth of 1 inch?
Generally, when you encounter areas of deep mortar deterioration, I recommend rebuilding these areas rather than attempting to repoint them. If the mortar is badly deteriorated to a considerable depth, the wall should come apart easily and the units can usually be cleaned and reused.
Although it may be possible to grind and repoint to a depth of 1 inch, or even to half the depth of the joints and still have an effective repair, I would still be concerned with the long-term performance of this repair. Leaving deteriorated mortar behind the new pointed material can greatly reduce the life of the repair.
Deteriorated mortar is very soft and readily absorbs water. Movement of the wall from thermal cycling, as well as from freezing temperatures, can force the newly pointed mortar out of the joints. This movement also can lead to spalling of the brick units from stress concentrations in their faces.
If the areas to be rebuilt become large and new brick need to be used, consider isolating the new units from the existing masonry. New brick masonry expands because of moisture, which can cause cracking or other problems in the existing masonry.