There are lots of reasons to make fake rocks out of plastic. Many people have big rocks in their garden. These look great, but are very heavy and can be difficult to move. If you’re the set designer for a play set outdoors, you need rocks that look realistic, but can be moved by stagehands between scenes. Making these fake rocks can be a fun weekend project and can be a way for you to flex your artistic muscles.
Decide what kind of rock you will make out of plastic. As you’ll remember from elementary school, there are three kinds of rocks: igneous, metamorphic and sedimentary. Sandstone (sedimentary) is a powdery, brown/red colored rock, while obsidian (igneous) is a shiny black rock. Rocks can also cleave in standard patterns or have jagged, waved edges. If you’re putting your fake plastic rock into your garden, think of what kinds of rocks can be found around where you live.
Use pre-formed pieces of plastic to serve as the basis for your rock. A gallon milk jug, for example, can be made into a rock without having to melt anything. Use a utility knife to remove the handle from the milk jug. (Rocks, you see, don’t have handles.) Use super glue or caulk or another waterproof adhesive to plug all of the holes in the jug. A crushed cottage cheese container can be recycled in the same way. Crush the container to obliterate the artificial shape and make the top part your plastic rock.
Make your rock from scratch. Craft stores have beads of easy-to-melt plastic that you can shape into a rock. Just find a rock whose shape you like and put it on something that won’t melt or burn. Pour the plastic onto the rock, carefully coating the whole thing. Once the plastic dries, you can use a utility knife to cut the plastic from the rock. Just glue the pieces together, and you have a plastic version of the real thing.
Paint your rock to look like a real one. (You are, of course, free to make your rock look unnatural, if that’s what you want.) Acrylic paints will do well and look realistic. Some rocks have pieces of shiny minerals in them. Mimic this effect by adding some well-placed pieces of glitter. If you’re making sandstone, sprinkle some fine sand onto your plastic rock before the paint tries to make it look genuine.
Seal your rock if you’re going to leave it outside for a long time. You can get shellac in a spray can that adds a fine layer of protection to your plastic rock. Shiny rocks, such as obsidian, could use a coat of clear nail polish to reflect the light.