A.A. Houghton's definitive 1910 treatise "Concrete From Sand Molds" describes how to use a sand mould as a "means for the reproduction in concrete of any work without limit to the size, shape or the degree of ornamentation upon its surface." If you need to make a custom concrete shape for a bit of free-form landscaping or a plant or water feature, sand moulds work well. Sand moulds have been used for concrete shaping for almost as long as people have used concrete.
- Skill level:
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Things you need
- Brick or beach sand
- Water hose
- Concrete trowel
- Small aggregate concrete mix
- Concrete shape you want to copy
- Plastic sand castle mould (toy)
Make a large pile of sand in your working area. Wet the sand with a hose till the sand holds its shapes when you press it between your hands. Test it with a child's sand castle toy mould. If the sand holds its shape when removed from the mould, it's the right consistency.
Dig out room in your sand pile to place whatever shape you are creating. For a bird bath bowl, for instance, dig a shallow depression. Turn the bowl upside down and press it firmly into the wet sand. Tamp the sand firmly around the model and then remove it carefully from the sand.
Mix enough concrete mix in the wheelbarrow. Make it wetter than you would for a sidewalk or slab. The sand will absorb water from the concrete, allowing it to set more slowly and making it stronger. You want it to pour into the sand mould without disturbing the impressions in the sand itself.
Spoon the wet concrete into the bottom of sand impression in even layers. Keep adding concrete, spreading it out till you can pour it without distorting the sand cast. Gently pat the surface of the mixture periodically with the trowel to remove air bubbles and prevent cracks.
Lay a plastic sheet over the sand cast and allow the concrete to cure for 48 hours.
Lift the concrete from the sand cast and brush away the sand from the surface. A light once-over with medium sandpaper will remove any stubborn bits from the outside of the concrete shape.
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