Make a Fake Rock Wall

In the following article, you will learn how to make a large-scale, temporary, fake rock wall. This type of wall can be especially useful for special event decorations, or as a prop for plays and other programs. This is only a guide, so let your creativity flow. This is how one particular wall was made, but you can adjust this to create your own special project.

Steps

  1. Hang sturdy paper on wall using a staple gun. Staple every 4-6" along the edges to ensure that the paper will hold the weight of the foam and portland. Overlap paper about 6" and seal off edges with packaging tape. Be sure paper is cut to about 1" larger than the area you want to cover. It will be trimmed at the end.
  2. Put on gloves and lay down a tarp. This foam is very difficult to remove from skin and other surfaces (tile, carpet, walls, etc). If you don't want foam on it, cover it up.
  3. Apply foam to wall, leaving about 1" around the edges to allow the foam to expand (again, we will trim this later). Shake the can thoroughly and hold it upside down when you spray the foam (as per instructions on can). Spray foam directly into gloved hand and smear a thin layer (1/4" or so) onto paper. Don't worry about spreading the foam into an even layer. Uneven layers will add texture and shape to your wall. As round bubbles appear, smooth over them with your gloved hand to shape the texture. Add any details now (like crags, shelves, etc) with the foam. Change gloves as needed (you may find that you need to change gloves after each can). Foam will expand for about 30 minutes. Cover entire area and let dry for approximately 2-4 hours, depending on how thick you applied the foam.
  4. Once foam is dry, mix the portland in a five-gallon bucket with enough water to create a paint-like texture. Using a large brush, "paint" the portland mixture onto the wall. It helps if you only mix a little at a time (make about 2 gallons, use it, then make more). Let portland dry on the wall overnight (or approximately 8 hours). Portland will dry a light grey color, but you can add cement dyes or stains in if you wish. These can be picked up at your local hardware store.
  5. Once Portland mixture is dry, use textured spray paint to create shadows and details on your wall. Pick colors that are natural and would look good with your other decorations (e.g. a spray paint with a thick, large-grained texture).
  6. Trim paper around edges (remember the 1" we left?) with an exacto-knife or razor blade.
  7. Add other props and embellishments to suit your needs.

Tips

  • A thick, sturdy, grocery bag paper stapled to the wall was used for this project. You can use other backings if you wish, just be sure they're sturdy and won't tear with the weight of the foam and portland. Consider plywood for this project if it fits your needs. If you want something portable and durable, plywood or OSB are options.
  • Be very cautious about using roofing tar paper, as it's extremely flammable.

Warnings

  • Spray foam WILL STICK to anything. Please be careful. Lay down tarps, cover walls near your project and wear gloves. This can be a messy project- be prepared!

Things You'll Need

  • Expanding foam in an aerosol can (I like "Touch & Foam Max Fill")
  • Latex or rubber gloves
  • Portland (Cement mixture without the rocks)
  • Water
  • Some sort of backing- we used heavy duty paper (grocery bag thickness), stapled to the wall.
  • Packaging tape
  • Staple gun
  • Tarp
  • Large paintbrush
  • {{safesubst:#invoke:convert|convert}} bucket
  • Paint Stir Stick
  • textured spray paint

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