I did a GOOGLE search for "licorice root mulch for tortoise substrate" and it came up empty. They DO use licorice root mulch in horticulture, but I haven't heard of anyone using it for a tortoise substrate. I would hate to experiment on your tortoise. See if the store will take it back and get coconut coir instead. And yes, you would need to either treat with water repellent or line with plastic.
thanks. sorry for the billion posts. this one was posted twice on accident and i posted the question in another thread so that i could get more responses. but, thanks for all the replies. i am ordering a new uvb bulb and will be returning the candy mulch to the store tomorrow