Making a Concrete Sink from Design to Production



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A nautilus shell was used as the basis for the sink design. Using the latest CAD software, the concept was converted to a 3-D rendering. Instructions for creating the 3-D pattern are transferred to a CNC router.

Foam-iT! 8 rigid foam is cast into blocks and used as the carving medium. The CNC router is used to carve the nautilus design out of the Foam-iT! 8 block. Additional segments are carved on the CNC router. Spray adhesive is used to adhere these foam segments together. Assembled segments are post-finished and prepared for making the mold.

Making a Mold Using the Cavity Pour Technique

Plastic strips are attached around perimeter of the model to extend the working mold surface. 1/2 inch (1.3 cm) non-sulfur based modeling clay is used to cover the model’s surface. Modeling clay will roughly conform to the model’s shape. Acorn nuts are placed on flange to create registration keys between support shell halves. Apply Sonite Wax to plastic flange to help release support shell.

Plasti-Paste II is mixed 1A:2B by volume, dispensed into clean mixing container and mixed thoroughly for 2-3 minutes. Spread Plasti-Paste II over entire surface to a thickness of 3/8 inch (1 cm). Plasti-Paste II is allowed to cure for 90 minutes at room temperature (73°F/23°C).

Remove the plastic strips from the model. Remove acorn nuts with a screwdriver. Remove clay from the cured support shell. Create vent holes in the support shell to allow the air to escape when the cavity is being filled with mold rubber. Drill three 1/2 inch (1.3 cm) holes in the support shell. The holes allow liquid rubber to enter the cavity.

Plastic is placed over sink drain and sealed with hot-melt glue to prevent liquid rubber from passing through. Support shell is placed over sink model. Glue is applied on the edge of the support shell to prevent liquid rubber from leaking. Clay is used to create a containment ring around the vent holes. Rings will contain excess mold rubber that may leak through vents. The clay is centered around the vent holes. Hot-melt glue is applied to modified drinking cup to create a funnel. The cup funnel is placed over the center of the pour holes.

Mold Star 30 platinum silicone rubber is dispensed 1A:1B by volume. Material is dispensed into clean mixing container and mixed thoroughly until there are no color streaks. Mold Star 30 is dispensed into the three pour holes. Liquid rubber is filling the cavity between the mold and the support shell. Let Mold Star 30 cure for 6 hours at room temperature.

Remove clay rings, plastic cup funnels, and plastic strips. Modeling clay is again used to cover the model’s surface, and plastic wrap is applied to help minimize cleanup. Clay is used to form an opening at the top of support shell where rubber will be poured, and will also function as a registration key. Acorn nuts are again used to create keys to register the rubber mold with the support shell.

Plasti-Paste II is dispensed, mixed and applied to second half, then allowed to cure for 90 minutes at room temperature. Support shell is demolded, and clay and acorn nuts are removed. Sonite wax is used as a release agent between new liquid rubber and cured rubber. Vent holes are drilled and highlighted with a green marker for easy identification. Both halves of the support shell are assembled. The mold structure is placed into a sturdy box for leveling. Hot-melt glue is used to seal the two halves of the support shell. Straps are used to secure support shell halves.

Mold Star 30 is dispensed, mixed, and poured into cavity. Even distribution of mold rubber inside the mold cavity will be indicated as the liquid rubber reaches the vent holes. Clay is used to stop the flow of the rubber at each vent hole. Liquid rubber will progressively seek higher levels within the cavity as lower vents are capped. Let Mold Star 30 cure for 6 hours at room temperature.

To demold, clay and straps are removed. Mold halves are carefully separated. Sink model is removed from rubber mold. A pour hole is created in the mold rubber using a razor knife.

Casting the Concrete Sink

Mold is secured to ensure a leak-proof seal between mold halves. White cement and additives are prepared. Concrete batch is mixed. Concrete is poured into the mold cavity and allowed to cure for 4 hours. Concrete sink casting is removed from rubber mold by removing the straps and carefully separating mold halves with a screwdriver. Perfect detail captured from the sink rubber mold in the concrete casting.

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Post time: 12-11-2016