Kitty litter is not such an odd choice as the article makes it out to be. The mineral variety is typically made out of sodium bentonite. This is well known for its ability to absorb more than its own weight in water, which also causes it to swell and therefore seal cracks, enhanced by its self-sticking capability. Kitty litter has a well-defined grain size and would be fine to use so long as one didn't switch brands. Wikipedia even lists a method for determining whether kitty litter has bentonite or not.