How to Make Your Own Molds for Stone

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If you have ever wanted to build a flagstone patio or make a stepping stone path, but live in an area with little natural stone, you probably know that buying it is expensive. You could turn to brick or cement pavers, but somehow they do not have the warmth and texture you want. There is a solution though --- if you do not mind a small compromise. Make molds and cast your own "stones" in concrete.

Things You'll Need

  • Stone(s)
  • Scrap plywood or heavy cardboard
  • Liquid latex rubber
  • 1- or 2- inch paintbrush
  • Cheesecloth
  • Foam runner scraps
  • Cardboard
  • Hot glue gun and glue
  • Plastic or rubber bowl
  • Wooden spoon
  • Rasp or sandpaper
  • Talc
  • Find a flat stone of the size and shape you would like to use. (You can borrow from friends or neighbors --- the molding process does no harm.) Brush away all dirt and debris.

  • Lay stone on a flat scrap of plywood or thick cardboard --- turn the best side up.

  • Brush on a thick coat of liquid latex over the entire surface --- including sides (but not the bottom) using a soft, 1- or 2-inch wide paintbrush. Let dry; repeat until you have a rubber coat about ¼ inch thick.

  • Give your mold extra strength. Cut a piece of cheesecloth the size and approximate shape of the stone plus extra to cover the sides. Place on the stone and brush latex over the entire surface, working it into the fibers with paintbrush --- gluing it to the previous layers. Dry; coat with one or two more layers of latex, drying between coats.

  • Examine rubber-covered stone for undercuts on its sides --- places where the mold will catch during casting. Ideally, your stone will have the shape of a very low, truncated pyramid in cross section (when viewed from the side). That is, it will be wider at the base and smaller toward the top. This shape allows the "mother mold" (the backing for the flexible rubber) to be pulled off without breaking the cast inside. If it has the described shape, skip the following step. If it has undercuts, proceed to the next step.

  • Fill all undercuts by cutting scraps of foam rubber and gluing them with latex to the areas of undercut; dry. Coat the foam completely with liquid latex and place strips of cheesecloth over them --- feathering them out across the mold as smoothly as possible. Dry; re-coat until the entire mold is smooth and no undercuts are visible.

  • Build a dam around the stone using strips of heavy cardboard cut about 2 inches taller than the stone --- tape them together as necessary, following the outline of the stone approximately 1.5 inches from the sides. Glue the cardboard to the base,with hot glue, making sure there are no gaps for plaster to seep beneath the walls.

  • Follow manufacturer's directions on package to mix a large batch of plaster of Paris in a plastic or rubber bowl with a large wooden spoon (or your hands). Pour over the rubber-coated stone and fill to within ½ inch of the top edge of cardboard strips. Let harden.

  • Pull away cardboard dam to expose the plaster. Trim away excess plaster and smooth rough edges with a rasp or rough sandpaper.

  • Turn mold over. Remove rubber-coated stone from plaster mother mold. Peel away rubber from stone.

  • Wash rubber mold in soapy water; rinse; dry. It is ready to be filled with cement for casting your own "stones". Dust with talc to store.

Tips & Warnings

  • Mold several stones of varied shapes and alternate their positions to create a more natural look.
  • Mix dry pigment into cement, or sprinkle into the molds prior to pouring cement to give "stones" natural color.
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