Concrete sinks can be small or large, elegant or rustic in style. They are used both indoors and outdoors. The mold for a sink has two pieces--an inner mold and an outer mold. The sink is formed in the space between the two pieces.
Instructions
Prepare the Mold
1. Carve a block of insulation foam into a plug for the drain hole. Screw it firmly into the hole in the inner mold. Work from the outside of the mold, so that the plug sticks down below the base of the mold.
2. Bend a length of the metal rod to form a shape that is one inch larger in all directions than the inner mold. Lash the overlapping ends together with wire. This will be the upper rim of the reinforcing mesh basket that will be in the center of the concrete.
3. Cut a section of the hardware cloth and fold it to make a basket. The base should be 2 inches smaller than the outer mold all around. When the sides are folded into place, they should be 2 to 3 inches shorter than the sides of the inner mold. Stitch the overlapped corners together with wire.
4. Mark a line all around the mesh basket at a height that is 4 inches shorter than the side of the inner mold. Place the rim at that height, and fold the edges of the mesh basket over the rim. Stitch the rim in place with wire.
5. Cut a hole in the bottom of the mesh basket to make room for the sink strainer.
6. Screw the sink strainer into the hole provided for it in the outer mold. The rim of the strainer should be about 2 inches above the bottom of the mold. Be sure the strainer is level.
7. Spread a thin band of non-hardening plasticine clay around the rim of the sink strainer. This will leave space for the plumber's putty when you install the sink. Make the clay as even as possible. Trim the edge with a knife.
8. Coat the exterior of the strainer with wax. Cover the top edge with plastic wrap. If you have a top of a yogurt container or a similar cover, place that over the plastic wrap.
9. Spray the interior of the outer mold and the exterior of the inner mold with nonstick cooking oil. This will make it easier to remove the sink from the mold when you are finished.
Mix the Concrete and Pour the Base
10. Mix the concrete according to bag directions, but replace half the water with concrete bonding adhesive. If you are using a coloring pigment, follow package directions to add it to the concrete mix.
11. Spread about 1/2 inch of the concrete mix in the bottom of the outer mold. Jiggle the mold and tap the sides and bottom to work out air bubbles. Repeat with another 1/2 inch of concrete mix.
12. Put the wire mesh basket into the outer mold on top of the concrete layer. The hole in the bottom fits over the sink strainer. Center the basket so that there is an equal amount of space between the basket and the outer mold on all sides.
13. Add 1 inch of the concrete mix over the bottom of the wire basket. Jiggle the mold and tap the sides and bottom to work out air bubbles.
14. Add more concrete mix, until the concrete reaches just to the edge of the sink strainer. Smooth the concrete with a trowel.
Pour the Sides of the Sink
15. Remove the plastic covers from the top of the sink strainer. Lower the inner mold into place. The foam plug on the bottom of the mold will fit into the sink strainer. If there is a gap, fill it with non-hardening plasticine clay. Clamp the molds firmly into place.
16. Fill the spaces between the molds with wet concrete. Pour about 1 inch or so of concrete at a time. Stop to jiggle the mold and tap the sides and bottom to work out air bubbles. Tamp the concrete mix down firmly with a dowel. Continue until the spaces are completely filled.
17.Smooth the top edges with a putty knife. In a few hours, when the concrete mix has stiffened, remove the clamps. Use a putty knife to clean up any rough spots.
Cure the Concrete
18. Cover the sink with a polyurethane sheet. Leave it in a warm, dry place for at least 3 days, while the concrete cures.
19. Remove the inner mold. If necessary, use a box knife to cut it away from the concrete. You can also use a small pry bar, but be careful not to pry against the sink itself.
20. Determine if there are any small holes or gaps in the interior of the sink. If so, fill them with a paste of cement and water tinted to match the concrete sink. Rub off any excess and let the patch dry completely.
21. Remove the outer mold. Patch any small holes or gaps in the exterior of the sink.
22. Apply a concrete sealer to the sink. Follow the manufacturer's directions. Even with the help of a sealer, the concrete will take 28 days to reach its maximum strength. You can put the sink in place without waiting that long, but protect it until it is completely cured.
