Grout is not a waterproofing agent. Water will soak into unsealed grout as well as pavers/bricks. In PA, a good freeze will cause the ice to expand inside the joint - same as it does in with rocks in the woods - the ice cracks the joints.

Also, when tiling/grouting - there is always a problem when two dissimilar materials/section are butted together (such as the curved grout meeting the curved concrete patio slab. Those materials will expand and contract at different rates - thus promoting cracking in their common joint. <<-- This is why a good installation should have a flexible joint between those surfaces (such as when a tiled shower have color-matched caulk used where two walls come together rather than inflexible grout or where the walls meet the shower floor). If those "joints" are rigid, they will always crack, absorb water/soap and grow mold deeply into the wall.

All naturally stone/bricks/grout/cementitious materials need to be sealed periodically or else they absorb dirt and water. This included granite/quartz/tiled countertops indoors as well as brick steps outdoors, etc.

Looks like you might want to have someone "repoint" your brick edging. And then, once done, seal the grout and brick as an annual maintenance task.

 

Thanks for the note. To clarify, the joint between the brick and the concrete decking is flexible mastic that looks like the pointing material, not grout.

I appreciate the general comments about waterproofing and grout. My main question is still what I should be using as the mortar for those bricks. The brick coping is loose and sounds hollow when tapped, so I'm going to need to do more than repoint them.

 

Good to know about the flexible mastic. That was done right in my book.

As far as new grout, if you're only going to repair the cracked ones you should use the same grout and color - else it would look bad.

If you're planning on pulling ALL the grout out, then you could move up to an epoxy based grout which will be less prone to cracking and separation. Laticrete would be a good choice. Materials and labor will be a higher cost plus, depending on color it may tend to yellow from the sun. You will still have to seal the bricks every year, since they need it.

 

Thanks again. I'm going to have to pull up all of the bricks to re-set them anyway since they've detached from the pool wall, so I figure I may as well clean them up and re-do the grout too. Appreciate the Laticrete recommendation.