How to make cement molds

Written by emily patterson
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Cement moulds create cement stones in unique sizes, shapes and textures. They may be as simple as squares, circles or other geometric shape for stepping stones, or detailed to resemble slate or other natural rocks. The variety is limited only by the imagination of the person who makes the mould. In addition to the variety of shapes, sizes and textures, there are many different mould-making products available, from cardboard or wood for geometric shapes, to silicone or clay for more detailed surfaces on the finished casting.

Skill level:

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Things you need

  • Heavy cardboard (such as a packing box)
  • Wood (fir strips or 2-by-4's)
  • Packing tape
  • Plywood
  • Silicone caulk (squeeze tube or for caulk gun)
  • Caulk gun (optional)
  • Screws
  • Screwdriver (or drill with screwdriver bit)
  • Silicone mould putty (available online and in many craft stores)
  • Cling film
  • Mold release agent (available at most home improvement stores)
  • Spoon or kitchen knife (optional)

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    Simple Geometric Shapes

  1. 1

    Create the edges of the form for the mould using cardboard or wood. Choose cardboard for moulds with rounded edges, irregular dimensions or simple straight-sided geometric shapes. Use wood only for straight-sided shapes such as squares, rectangles or triangles. Wood is the best choice for moulds that will be reused many times.

  2. 2

    Cut the cardboard into widths approximately 4 inches wide. If a more solid and reusable mould foundation is desired, instead of cardboard, use wood cut to the shape needed, provided the desired mould is a simple square, rectangle or other straight-sided shape.

  3. 3

    Tape the cardboard into place in the desired shape on the plywood by placing one edge of the cardboard against the plywood to create a 4-inch deep form. Tape from the outside of the cardboard so the tape does not create indentations in the concrete when it is poured into the form. If using wood, screw the wood to the base from the underside of the base. Apply a bead of silicone caulk around the entire inside of the mould (cardboard or wood) to prevent concrete from seeping out the edges.

  4. 4

    Spray the entire surface well with a mould release agent before pouring the concrete into the mould.

    Detailed Surfaces

  1. 1

    Create the outline of the mould as in the previous steps.

  2. 2

    Soften the silicone mould putty by kneading it and then pressing it into the mould to cover its entire bottom.

  3. 3

    Lay a thin sheet of cling film over the silicone putty.

  4. 4

    Press the desired textured object -- slate pieces, bricks or whatever you want the finished surface to resemble -- onto the cling film. Remove the pieces and the cling film. Use a knife, spoon or other appropriate instrument to etch additional details into the mould.

  5. 5

    Allow the silicone putty to dry according to the manufacturer's directions before spraying it with mould release agent and filling with concrete.

Tips and warnings

  • Pour the concrete into the mould slowly and steadily for an even finish. Tap the sides of the mould gently after filling to help air bubbles rise to the top.
  • Apply the spray release agent in a well-ventilated area to avoid inhalation of fumes.

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