Hi, I have a concrete stair with stone veneer on the outside. Some of the mortar joints need repair. What should I use to tuck-point the mortar joints? The size of the joints varies from 5/8" to 1 1/4". I used Type S mortar mix from Menards before but the repaired joints crack again within a year or two. Here is a picture. Thanks!

 

If the cracks return it's not the mortar its the material/wall is moving causing the cracks to reappear.

What's behind the stone?

 

I believe the middle are cinder blocks. This is on the outside of a retaining wall of 7 or 8 concrete steps going to the front door.

 

Looks nice..

If the concrete steps are not on a footing below frost, the whole thing is going to move, breaking the mortar.

Or, even if the concrete steps ARE on a footing below frost, if the stone veneer is not, and it's resting in the dirt (basically hanging on the steps) the frost could heave the veneer while the steps stay stationary.

Or maybe the veneer was not anchored back into the concrete steps with straps (brick ties) periodically as the veneer was laid up.

Or possibly the consistency of the mortar was poor the first time... too dry and the brick pulls too much moisture out too quickly, ruining the bond. Not dissing Menards but I have heard complaints about the quality of some of their mortar products. If it's not "sweet enough", lacking enough cement or lime in the premixed recipe, you are going to have poor adhesion and low strength.

But often, a diy project like that fails due to working too slowly. Mixing up a batch of mortar, taking too long to put the bricks on allows the mortar to dry out as you go, making for an inconsistent quality partway through. Adding water to reconstitute the dry mortar weakens the mix as well, if that happened.