How To Make Custom Foam Hollow Rocks for Outdoor Speakers


Ez-Spray® expandable rigid foam is often used to create large, lightweight elements used in landscaping. It also increases productivity by reducing production time. In the following example, the goal is to create custom, hollow, rocks for the purpose of concealing and housing outdoor speakers that blend in with exterior landscapes.

Using a Rebound® 25 mold previously used to create decorative rocks cast in concrete, the landscaper quickly uses the EZ-Spray® system to quickly produce durable, lightweight castings. Outdoor speakers are then mounted inside. The rock speakers add concealed audio ambiance to any environment.   

Materials Used in this Tutorial

  • EZ-Spray Foam
  • Knife
  • Mixing Sticks
  • Mixing Containers
  • Rebound® 25
  • Niosh Mask
  • Taupe Color Spray Enamel
  • Polyurethane Stain

Step 1: Preparing Your EZ-Spray Foam

Open an Ez-Spray® foam cartridge by prying off the tip of the cartridge. Install a flow regulator (included) before adding the static mixing tube. Install a static mixer (included) on the cartidges. Then, tighten the collar over mixer tube and load the cartridge with the mixer into the EZ-Spray® gun and attach the air line hose.

Note: gloves are recommended when working with any materials.

Step 2: Spraying Ez-Spray™ Foam Into Your Mold.

To start the gun, eject a small amount of material into a waste bucket. This is done to ensure a good mix and to put only the well mixed material into the mold. Position the Rebound® 25 brush-on mold to complete the support shell for spraying. Wear a Niosh approved mask.

Be sure to deliver an even coat across the surface of the mold. The foam will quickly begin to expand and form the hollow shell. Add another quick coat to ensure a strong, even piece.

Step 3: Demold Your Foam Rock

Allow the foam to fully cure before demolding. The Rebound® 25 silicone glove mold will easily peel from the casting. The finished casting displays excellent detail. Extra material can carefully be cut away with a utility knife.

Step 4: Finishing Your Speaker

Spray taupe color enamel to the surface and allow it to dry. Then, brush a polyurethane stain over the surface to add variation and depth.

The faux rock speaker blends in to the surrounding landscape while delivering audio ambiance. The manufacturer offers several sizes and finishes. Several custom speaker rocks were installed around the property to deliver balanced audio without being offensive to the natural landscape.