Stone Master Molds small keystone mold creates 4 separate keystones with a chiseled stone texture on the front and smooth sides. Each keystone is 5.75" long, 4" wide at the top, 2" wide at the bottom, and 3" thick. You can pour them thinner, as desired. Save money and create your own custom color using our professional quality rubber keystone mold that can be used for hundreds of pours. No need for a release agent. Manufactured Stone Basic Mixing Procedures Using A Pre-bagged Concrete Mix: This is one suggestion for mixing the concrete for manufactured stone. There are many other instructions available online, including videos. BE SURE TO USE A CONCRETE MIX THAT CONTAINS PORTLAND CEMENT. We recommend Sakrete Maximizer, as it has lightweight aggregate, is high strength, and yields more product, but there are many kinds you can use. Follow the manufacturer’s instructions for mixing. If using pigment, add desired iron oxide pigment to mixer (100% pure, no additives). These can easily be found on Amazon, etc. A plasticizer can be added to reduce the amount of water in the mix. Pour into the molds which may already have coloring additives… NO RELEASE AGENT NECESSARY. Vibrate molds to release air bubble. Cure in the molds for approximately 24 hours at the minimum of 70 degrees Fahrenheit before demolding. Higher humidity is desired. Molds can be covered with a tarp to retain more heat and humidity. Continue to cure demolded stones at 70 degrees or greater until ready.