muriatic acid is an acid, and will react with baking soda to form salt and water (remember the volcano we made in school- lots of foamy crap from baking soda and vinegar; muriatic is really concentrated vinegar!)
pour small amounts of baking soda through cracks, add more as foaming stops (may have to add some water, if acid is dryed or soaked in...)
keep adding til no more reaction, then add about a cup more- the excess baking soda will absorb the smell!
do only a little at a time, to prevent excess reaction and foam!