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Building Artificial Rock Forms

How to build an artificial rock form?

There are a number of different methods to build a form for your artificial rock. For the purposes of this instructional guide we will be building a "non-structural" form since the finished product is not intended to be load bearing. A rock climbing wall or similar structure which absolutely must have structural integrity to avoid liability and safety issues should not be attempted by anyone but professionals.

Structural form design would involve a complex grid work of custom bent steel reinforcement making a basic skeleton of massive strength. This would be then subject to approval by building inspectors and structural engineers. For non-structural we will be using Styrofoam to create our basic void which is designed not to provide long term support, but short term support until the concrete has cured. It can be left in place as added strength, or removed to create a hollow artificial rock commonly used for landscaping. Either way the overall strength is derived from the concrete and is not suitable for load bearing purposes.

Styrofoam is a good choice because it is cheap, readily available and easy to work with. You can leave it in after the concrete has cured and won"t biodegrade or rot like wood would rot with time. For this reason foam also makes the artificial rocks suitable for indoor use.

Materials required for building an artificial rock form

-2 inch thick styrofoam (most commonly sold in 4x8 sheets)
-Tin snips
-Tie wire or copper wire
-Razor knife
-2 inch diamonds chicken wire
-2 inch squares steel mesh

A good artificial rock form will make the sculpting process MUCH easier

You will start by cutting pieces of styrofoam to make the bulk of your form. You will be layering pieces of foam on top of one another to create the basic size and shape of your rock. The layers are attached by bending pieces of wire with a 90 degree hook at one end and piercing through multiple layers as per the pictures below. The friction will cause the wire pins to grasp and hold together the pieces of foam

NOTE: If you plan to remove the foam after the rock is completed to have a hollow artificial rock you should use a styrofoam adhesive instead of wire pins to hold the bulk of the form structure together. This will minimize the danger of having sharp steel protruding through the styrofoam that you will be removing later BUT involves a much slower and messy form building process since you will need to allow time for the adhesive layers to cure before proceeding to the next step.

Next you will want to create slopes on the sides of your form. You will do this by adding layers of custom cut pieces of foam that gradually build up the sides of the artificial rock form. You can also carve off from the existing rectangular form to create an overall rock like appearance.

Remember that you will be applying concrete over the form so you will want to undersize your artificial rock form to ensure that the finished product is the size you want. Once you have you the styrofoam form the shape and size that you want you can proceed to one of the most commonly asked question in artificial rock making - how will the concrete stick to the sides of the form?