In this tutorial the model is a concrete sink basin. To begin, measure the sink basin for dimensions. Use acrylic coated boards to construct the mold box walls, spacer board, and two baseboards. Center the basin on the acrylic coated board, and draw a pencil outline around the perimeter of the basin.
Use a jigsaw to cut out the circular pattern and then remove the plug. This will be used as a spacer. Place the sink on the baseboard and then place the spacer on top. Mark the alignment on the baseboard and spacer board. Use modeling clay (sulfur free) to create a gasket around the perimeter of the basin to prevent rubber from going underneth the model.
Place the spacer down over the basin and use modeling clay to fill in negative space caused by the spacer. Glue down acron nuts in the corners for the registration keys and place one extra acron to help with alignment. Assemble the mold box with drywall screws and seal the seams with hot melt glue. Release all surfaces with Universal Mold Release.