Use fake rocks in a garden for decoration or to conceal spare house or shed keys. Use fake rocks made from plastic latex in planters or indoor plant pots as well. You can make fake rocks easily from a clay mould and liquid latex casting compound. After you master the latex moulding technique, you can make a variety of fake rocks and experiment with different sizes. Choose a palm-size rock with lots of definition to make a mould from which to make your first fake rock.
Measure the rock's height. Locate a box that is at least 1 inch wider, 1 inch longer and 1 inch deeper than the rock. Press oil-based, sulphur-free modelling clay into the box until the clay is 1 inch deeper than the rock. Sulphur reacts chemically with the latex moulding plastic. Wet your fingers and evenly smooth the clay's surface.
Press the rock into the clay until just the very bottom of the rock protrudes from the clay. Because the rock will rest on the ground or in soil, you can make a one-part, press mould that is easy to make and use. Wiggle the rock slightly to lift the rock out of the clay.
Pour 1 cup of latex moulding compound, also called liquid latex casting compound, mask latex or slush latex, into a container. Purchase latex at craft, hobby and mask supply stores.
Pour 1/4 cup of dark brown or dark grey latex-based paint into the latex. The Costumer's Manifesto website maintains that mixing the colourant, or latex-based paint, directly into the liquid latex is the only way to eliminate paint from eventually flaking off or drying and cracking. Mix the paint and latex well with a plastic spoon.
Add more paint, 1/4 cup at a time, until you reach the colour desired for your fake rock. If you add more than 1/4 cup of paint, also add 1/8 cup latex compound per additional amounts of paint. Too much paint will compromise the latex.
Pour latex moulding compound into the clay mould, filling the mould completely. Monster Makers website explains that latex casting compound is a room temperature setting latex that transforms into a solid product without the application of a heat source.
Allow the latex compound to congeal within the mould for about an hour. Turn the mould over and pour the excess latex into the latex container. An outer, hollow shell or skin remains within the mould. Allow this latex to dry for about 48 hours. You can make a solid fake rock by leaving the latex in the mould instead of pouring off the slush, but this can take a week to dry completely.
Remove the latex plastic rock from the clay mould by carefully peeling the clay away and lifting the fake rock out. Turn the fake rock over with the hollow core resting on a flat surface. Allow the fake rock to air dry until completely dry to the touch.
Dip a sea sponge into black latex-based paint. Dab the sponge onto the fake latex plastic rock to create textured surface colour. Allow the paint to dry.
Always use latex in a ventilated area.