[Ron6519]

The is a company called Sika that makes a tenacious sealer. It comes in 2 size caulking tubes and a few colors. You can use that to seal against water.
You can pick it up at Home Deopt or mason supply stores. There are other similiar products on the market if you can't get that one.
Ron

 

[vsheetz]

Might try this: Deck-o-seal is used on a pool to fill the intentional ~ 1/2 gap between the pool coping and contrete walkways. Lasts for years, flexible, etc. Available at any pool supply local or online. http://www.deckoseal.com/