How to Make Fake Rocks Using Expandable Spray Foam

- Dry sand.

- Expanding spray foam.

- Old newspapers.

- Old rags.

- Disposable gloves.

- Goggles.

- Dust mask.

- A couple of paintbrushes - one for the initial coating, another one for the final touch.

- Acrylic paint in various colours (shades of grey, dark green, brown).

Steps

1. Prepare the Workspace

- Choose an area outside to work because the process can be messy.

- Prepare the area for spraying the foam. You can do this by spreading old newspapers and rags on the working surface. Wear your protective gear (gloves, goggles, dust mask) especially when handling the foam.

2. Build a Solid Foundation

- Take handfuls of dry sand and start piling it according to the size and the design of your rock. The piled-up sand should not be too small; otherwise, it will be unstable. Use your hands or a small spade to shape and smoothen the sand into the desired rock form.

3. Spray the Expanding Foam

- Shake the spray foam can well and start covering your rock shape, from the top down, with a layer of spray foam. This is the ‘first foam coat’.

- Be sure to follow the instructions on the spray foam can for proper use and application. Don't spray too little because the foam will then stick to the sand and not to itself, and the entire rock will be too crumbly.

- Don’t go overboard while spraying the first layer either, as the more foam you spray on, the smaller/squashed your rock will become. Just spray on a thin layer.

- Let the foam expand - it will double its volume.

- While the sprayed foam is expanding, gently spray it with water to keep expanding even further.

4. Create Texture and Cracks

- Spray the top of the foam with water so that it won’t get too hot when you touch it.

- Start cracking the foam by hand. Use your fingers to make fissures and cracks in the wet foam.

- For a more rugged, rougher look, start ripping strips of foam.

- Don't forget about the sides of your foam rock: keep shaping it and creating cracks with your hands. Feel free to use some of the old newspaper to gently rip the foam in various places.

5. Apply the Second Layer of Foam

- Once you are satisfied with the cracked foam’s texture, wait for it to dry.

- Spray a second layer of foam over the entire rock. Don't use too much foam. The aim is to fill any gaps in the first layer.

6. Carve your Rocks (Optional)

- Once the second layer is dry, you can start carving the foam with a sharp craft knife or a box cutter to give your rock a more natural and irregular shape.

7. Paint and Finish Your Rocks (Optional)

- Once the rock is completely dry (after 24-48 hours), paint them or finish them according to your preference.

- Paint to resemble the stones you would like them to look like. Don’t feel you have to limit yourself to greys and browns. Feel free to experiment by adding some darker or brighter shades.

- Paint some spots that will resemble moss patches.

- Let the paint dry completely.

- To give your rocks a ‘wet’ look, you can spray them with a semi-gloss clear coat spray paint.

- Your faux rocks are ready to be used in your garden or inside the house.