These molded concrete stepping-stones may take more work than commercial stones, but they offer you a chance to express your creativity.
1. Create your design. Roll oil-base modeling clay to 1/4-inch thickness on a work surface. Draw desired patterns on paper and place them on the clay. Cut around each pattern with a knife. Place clay pieces on an uncut copy of a stepping-stone size paper pattern (about 12x12 inches), which has been glued to a plywood work board. Sculpt a design model by shaping and joining clay pieces. Spritz with nonstick cooking spray.
2. Prepare the mold. Brush a thin layer of mold latex over the surface of the clay model. Apply slowly to prevent air bubbles. Dry overnight and repeat the process until the mold reaches 1/4-inch thickness (20-25 coats for reusable molds). When thoroughly dry, remove mold from the clay model and boil for 10 minutes to strengthen the latex.
3. Build a frame. Make a shallow square box to hold the rubber mold. For the box frame, use 1x3-inch pine furring strips cut to the size of the mold, and secure strips with screws. Use a square of Masonite for the bottom of the box. Insert rubber mold, design side up, in box.
6. Allow to cure. Smooth the top with a trowel and tap the box on the work surface to remove air bubbles. Allow the concrete to set for 24 hours out of direct sunlight.