Using Cardboard Tubes for Concrete

In the building industry, water-resistant cardboard tubes are used to make concrete posts. They can also be used as molds to make simple columns.
Using these standard cardboard tubes as part of the armature really increases the range of forms you can make.

Difficulty: Moderate

Instructions

Things You'll Need:

• 36-inch-long cardboard tube with 6-inch diameter Metal mesh such as hardware cloth Wire cutters 20-gauge galvanized wire Pliers Sand premixed concrete Water Mixing bucket Trowel Polyurethane sheet Concrete bonding adhesive Rubber gloves Mother-of-pearl fragments (optional)

Assemble the Armature

1. Cut a semicircle along one edge the metal mesh.

2. Cut a second semicircle parallel to the first and 27 1/2 inches away. You will now have a long, curved piece of mesh that is 27 1/2 inches wide.

3. Fold the curved mesh piece into a cone. Slip the cone over the cardboard tube. The tube should stand upright, so that the cone forms a wort of skirt around the base

4. Stitch the overlapping edges of the cone together with wire.

5. Cut a second piece of mesh to 24 by 24 inches. Fold it into a tube.

6. Slide the mesh tube over the top of the cardboard tube. Let its bottom rest against the mesh cone, and pull it snugly over the cardboard tube.

7. Stitch the overlapped sections of the mesh tube together with the wire. Lace the bottom of the mesh tube to the mesh cone with wire. The mesh tube will be taller than the cardboard tube.

8. Snip tabs into the extra mesh at the top. Fold the tabs over the cardboard and down into the cardboard tube.

Cover the Armature with Concrete

9. Prepare the concrete mix using a little less water than required by the manufacturer's directions. You want the mix to be quite stiff.

10. Scoop small amounts of the mix onto a trowel, and gently press the mix into the mesh. Cover the entire form. Don't try to smooth the surface.

11. Cover the form with a polyurethane sheet. Wait until the concrete stiffens.
    Seal the bucket containing the wet concrete mix, so it will remain wet enough to use later.

12. Paint the surface with concrete bonding adhesive.

13. Apply a second coat of concrete to the form. Pat the second coat to smooth the surface, or trowel it smooth.

14. If you want the finished pedestal to sparkle, press fragments of mother-of-pearl into the top layer when the concrete is stiff but still pliable. Dampen the shells first, so that they do not pull moisture from the concrete mix.

Cure the Concrete

15. Place a polyurethane sheet over the pedestal to hold in moisture.

16. Leave the concrete in a warm, dry spot for at least 3 days. Then you can remove the plastic.

17. Let the concrete continue to cure and become stronger for 28 days. Handle the pedestal gently during this period.

Tips & Warnings

• Wear rubber gloves when working with concrete. Rinse your hands with vinegar when you are done working to neutralize the alkalinity of the concrete.
• If you get wet concrete on your skin, wash it off promptly.

Resources

• The Portland Cement Association