Concrete is composed of cement, sand and/or gravel, and water. Cement is the key ingredient to any concrete, being the "binder" or glue that holds all the other components together.

Pre-mixed concrete can vary significantly in the relative proportions of cement, sand and gravel. Mixes high in crushed rock or gravel are common in commercial concrete, but for pouring stepping stones, excessive amounts of gravel can mar the detailed finish on a stone. High cement content mixes create a smooth, consistent surface finish, but are slightly more expensive. For a very high-detail, smooth finish, mortar and stucco mixes are ideal. These contain no rock or gravel, just sand and cement.

Mixes also harden at different rates, depending upon temperature and the percentages of cement in the mix. The more cement, the faster the cure. The warmer the ambient air temperature, and/or the warmer the water added to the dry concrete, the quicker the set time. To produce strong, durable stepping stones aim for a slow, cool, damp cure. Concrete curing is a chemical process, not a drying process.

The percentage of water added to a concrete mix is the number one factor affecting the strength and quality of your finished stepping stone. The less water, the stronger the concrete. But for the purposes of creating stepping stones with high-definition detail, you'll have difficulty getting an overly-stiff mixture to settle into the nooks and crannies of a mold. So try striking a balance between a thick and thin mix- muffin batter or thick pancake batter is good. Start with a little less water, blend well with the concrete or mortar mix, then add more water a little at a time until you reach the desired consistency.