Step 3. Soak the pre-made stepping stone in a water bath making sure both sides are thoroughly wet. This will help prevent the stone from soaking the moisture out of the mortar too quickly, which could cause cracking.
Learn How to Make Stepping Stones for Your Garden - You don't have to spend a fortune on stepping stones, or even kits to make them... Follow along with these suggestions and learn how to make them cheap and easy! (http://familycrafts.about.com/cs/steppingstones/a/040201a.htm)