How to Make a Cast of a Wall

Measure the surface area of the wall to determine the amount of material you’ll need for coverage. Take the length of the wall and multiply it by the height to get the area. Purchase enough rubber mold mix, fumed silica, sealing agent and mold release spray to cover the area plus an additional 10 percent to account for spillage.

Place drop cloths along the base of the wall to catch any falling molding materials.

Cover the wall with a brush-on sealing agent to seal any pores in the wall’s surface. The rubber mold mix acts as an adhesive and without adequate protection to the wall will stick in place. Allow the sealant to dry in place for the time recommended by the sealant manufacturer.

Split the wall into sections using a piece of chalk to draw each section onto the wall face. By working in sections, you can create a series of molds that cover the entire surface of the wall. Keep the sections easily manageable, with each about 3 to 4 square feet in size.

Spray the surface of the wall with a mold release spray to create a protective coating that prevents the rubber from adhering to the wall’s surface.

Put on a pair of rubber gloves. Mix the silicone rubber mold mix in a large bucket. Add the two components of the mix into the bucket, using the mixing ratio recommended by the manufacturer. Stir the mixture with a wooden stir stick until there are no streaks from the separate components remaining in the mix. Add a blue tint to the mixture to color the rubber. This will help you determine precisely where the rubber is applied to the wall when brushing it in place to avoid missing any sections.

Apply the mix to the wall using a stippling motion. Tap the rubber in a light layer with the brush. You should have full coverage with this layer but should still be able to see the detailed shapes in the wall surface through the rubber coating. This will capture the detail of the wall without adding air bubbles to the surface of the mold. Cover a full section of the wall with the light rubber layer, working from the top of the section downward. Wait for the rubber to cure to a tacky state in which it remains sticky but doesn’t come off if touched with a gloved finger.

Apply a second layer of rubber using an untinted batch to see where the rubber is applied. Brush the rubber in place with the paintbrush, creating a layer that’s about 1/8 inch thick. Wait for the second layer to become tacky.

Put on a dust mask, then mix a bucket-full of a batch of the fumed silica in unsaturated resin. The fumed silica will thicken the rubber covering once applied. Mix the fumed silica until it’s the consistency of bread dough. Add a bit of red tint so you can distinguish the fumed silica mix from the rubber beneath. Spread the fumed silica over the rubber with a wooden stir stick, building it up to a 1/4-inch layer on top of the rubber surface. Use the fumed silica mix to fill in any undercuts in the wall's surface, creating a flat covering over the wall.

Brush on a layer of the rubber sealant, covering the mold. Allow the mold to cure overnight, then peel it from the surface of the wall.

Repeat the mold making process for the remainder of the wall. Number the molds with chalk and mark down the location of each section so you can reassemble the wall once it's cast.

Create a frame for each of the mold sections large enough to contain the mold and a 1/2-inch piece of veneer placed on top of the mold. Use 1/2-inch plywood sheets cut with a table saw to fit around the mold as the base and walls of the frame. Screw the frame together using wood screws driven in place by an electric drill with a screw bit. The mold should be a box shape with a flat bottom and four sides. The interior of the box should be large enough to fit the entire rubber mold laying horizontally on the bottom of the box, with sides that rise 2 inches higher than the surface of the rubber mold. Place each mold into its frame, numbering the frame to avoid mixing the mold sections.

Mix a batch of concrete in a wheelbarrow, using a hoe, until the mixture is the consistency of thick cake batter.

Spray each mold with the mold release spray, including the frame sides. Fill the frame with the concrete to the frame’s rim. Tap the sides of the frame with a mallet to settle the concrete within the frame and force any air bubbles to the surface. Allow the concrete to cure for about five days until it's firm. Remove the concrete from the frame and allow it to cure a further 16 days. With all of the sections fully cured, you'll have a complete cast of the wall.