How to Make Fake Rocks Using Expandable Spray Foam
Although its intended use is as an insulating building product, expandable spray foam can also be used to create craft projects such as fake rocks. The rocks make lightweight but realistic additions to model railways, garden landscaping and as special effects for Halloween displays. The foam rapidly expands to twice its size or more, so a single can will make a good-sized boulder or a pile of smaller stones.
Things You'll Need
- Flat work surface
- Cardboard or newspaper
- Disposable gloves
- Disposable shaping tool
- Knife (optional)
- Rasp (optional)
- Latex paint
Instructions
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Choose a flat work surface in a well-ventilated area. Place newspapers or a piece of cardboard on the work surface as a base for the fake rocks.
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Put on disposable gloves. Shake the can of foam for one minute. Attach the spray tube included with the foam. Touch the tip of the nozzle to the cardboard and press the trigger on the spray can to dispense the foam.
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Lift the dispensing nozzle up and away from the cardboard base as the foam is dispensed. Dispense the amount of foam necessary to make the desired rock size, keeping in mind that the foam doubles in volume.
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Shape the foam before it sets using a disposable tool such as a paint stir stick or plastic utensil. Keep the shape as random as possible to emulate real rocks. Add more foam to fill any unnatural voids or change the shape of the rocks. Leave some areas of foam untouched to create a difference in surface texture.
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Allow the foam to cure according to the package directions. Use a knife and hand rasp to shape the foam rock after it has fully cured if desired. Paint the rock to give it a realistic appearance. Use latex or water-based paint since some solvents may dissolve the foam.
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Tips & Warnings
The spray nozzle will seal shut as the foam cures, so you must use all of a can of expandable foam at once.
Construct larger rocks using scrap wood or expanded polystyrene foam blocks as a framework to support the foam. Cover any gaps or open holes in the framework with plastic wrap to reduce the amount of foam necessary.
Expandable spray foam is very sticky. Assume that the foam will stick permanently to anything it touches, including skin.
Most spray foams are flammable as they are being dispensed and remain combustible after they cure. Follow the safety instructions on the can of foam.
References
Resources
- Photo Credit Photos.com/Photos.com/Getty Images
