THREE: SPRAYING AND BACKING

Step 2 – Spraying

• For full instructions on spraying, check out the Spraying GFRC Guide.
• Begin spraying the face coat in the edges.
• Be sure to blow out any loose material before spraying over it. This can trap unmixed sand and will result in a poor finish. Practice spraying before attempting a large project like this.
• Continue spraying the base and then the walls, working in a circular motion, until a uniform layer about 1/8″ thick covers the inside of the form.
• Take care spraying the vertical surfaces, especially on a tall form like this. Spraying the concrete on too thick will cause it to sag, which will be visible in the finished piece.

Step 3 – Cutting the Casting Blend with Basalt Fiber to Create the Structural Backer

• Basalt Fiber can be added to the remaining Casting Blend to create fibrous mix that will be laid up over the face coat.

Step 4 – Backing

• After the face coat has dried slightly, the structural backer can be applied.
• Pack the backer mix into the form by hand. Build up the thickness of the walls to 1″.
• Smooth the backer mix over the edges of the form walls to get it to hang.
• Be careful not to press the backer through the face coat, and work gradually on the vertical surfaces to limit slumping.
• Do not spray or cover the 1″ thick disc knockout. Build up a uniform thickness around the knockout, and smooth the top so the edge of the knockout is still visible.
• Let the vacuum run for a few hours until the concrete has cured enough that it doesn’t change shape when the vacuum is turned off.