Just a note on the muriatic acid. As it might eat away the hard block slowly it will also eat away at the block material at a faster rate. Also if anyone is thinking of using muriatic acid for rust removal , don't do it in your garage, the fumes will kill you before you can get out, also the fumes will rust every piece of bare metal in the garage. Do it out side with a good breeze blowing away from anything that you might like to keep, also wear rubber gloves and eye protection . I other words, muriatic acid is some bad $hit.