Wet masonry mix is extremely caustic, so protect your hands with rubber gloves. Plan to use about 1 gallon of ready-mix for each 12-inch stone. For many stones, it's often cheaper to use this recipe: 3 parts masonry sand, 1 part Portland cement type 1, and approximately 1 part water. Blend dry ingredients thoroughly until mixture is one color. Make a well in the center of dry mixture. Pour water in well; mix until it is the consistency of custard. Use immediately.
1. Create the mold. Fill any 12-inch-diameter plastic container with damp builder's sand to within 2 inches of the top. Trowel to level. Arrange leaves or other natural elements on sand. Press leaves in place vein side up. Embed a mix of shells, rocks, or pottery in the sand, keeping in mind that the side placed in the sand will be visible after the stepping-stone dries.
2. Pour the mix. Taking care not to disturb leaves, pour ready-mix into mold. Trowel to settle cement, release air bubbles, and bring excess water to surface. Avoid over-troweling or digging into sand. The surface should be smooth and level.
3. Cure and unmold. After curing for 48 hours in shade, loosen the mold and invert onto plastic. Trowel off excess sand. (Some sand remains for texture.) Hose off and remove leaves with fingers or use a fingernail tool. Some leaves may need to dry for 2 to 3 weeks before you can remove them.