Real rock walls can be expensive and difficult to install in your home, but often all you want is the appearance of rock on your wall for your home decor. A faux rock wall gives you all the appearance of real rocks without the weight, difficulty, and expense of an actual rock wall. You can install the faux rock wherever you want, since it doesn't require a wall that can support the weight of natural rocks; and you can install it quickly since you don't have to transport and install actual stone.
Measure the area where you wish to install your faux stone wall. Cut plywood to fit your area, and then paint it grey. Once the paint has dried, screw the plywood to the wall into the wall studs (use the stud finder to locate them).
Create forms for your rocks out of bowls, boxes, or whatever disposable containers you want. Use several different sizes and shapes to get a variety of "stones" for your wall. Line the inside of the forms with plastic wrap.
Mix a small test batch of the foam producing liquid, and put them in your smallest mold. Note that the liquid can expand many times as it transforms from liquid to foam. Check the foam instructions to ensure that the foam fills the mold completely, but not too much. Once the foam has cured (consult your manufacturer's specifications), remove the foam from the mold. Make sure the plastic releases from the foam, and that the faux stone has the texture you want.
Adjust the appearance of your forms by loosening or tightening the plastic wrap in the forms. Secure the plastic with duct tape when it is where you want it to be. Line up all your molds where you can easily reach them. Calculate the amount of liquid you will need to mix to fill all your molds with foam.
Mix only enough liquid to fill your molds. Quickly fill the forms with the liquid. Wait for the foam to cure, then remove the faux stones from the molds. Repeat this process until you have enough stones for your wall.
Paint the stones with textured spray paint. Use different shades of textured spray paint to create the appearance of different types of stone. Allow the paint to dry completely.
Glue the faux stones to the plywood with hot glue. Leave about 1/2-inch space between the stones to give the appearance of mortar between them (The gray paint on the plywood will mimic the color of mortar.) Vary the order and location of your different types of stones to give a more natural appearance.