Rock-solid planter

  • Image credit: Reed Young
  • Illustration by George Retseck
  • Image credit: Reed Young
  • Image credit: Reed Young
  • Image credit: Reed Young
Date:1 August 2012 Tags:, ,

Concrete is just as useful and versatile today as it was when the Romans discovered how to make it 2 000 years ago. Early masons used the humble mix of cement, sand, stone and water to build impressive structures such as the Pantheon (AD 126), which is still in use as a house of worship. With its stout granite columns and massive concrete dome, the Pantheon gives new meaning to “built to last”.

Today, we use concrete for everything from home foundations to kitchen counters. It’s also a great material for making smaller items, such as the planter shown here. Super-sturdy but simple to build, it requires the construction of inner and outer wood forms to mould the finished product. Basic carpentry tools, a wheelbarrow and a 40 kg bag of concrete mix are all you need to do a job that would make a Roman proud.

For planter plans, see image 2.

1 Form and cast
Screw together the inner and outer forms. Coat the exterior of the inner form with glue, and cover the surface with aluminium foil. Do the same for the inside face of the outer form. Spray cooking oil on the foil surfaces.

Place the inner form, top-down, on the mounting board. Screw through the bottom of the board into the form’s cross supports. Place the outer form over the inner one, and use angle brackets to secure the outer form to the mounting board.

Empty a 40 kg bag of pre-mixed concrete (ask for the kind made with river sand) into a wheelbarrow. Add about 150 g of buff (a sort of yellowish-brown) liquid cement colour to 4 litres of water in a bucket. Add the tinted water to the powdered concrete a couple of cups at a time until the mixture is malleable but not runny.

Pour the concrete into the form (left, top). Repeatedly plunge a scrap-wood stick into the concrete to consolidate it. Over-fill the form, then run an oscillating sander (without sandpaper) over the entire form to vibrate out voids. Strike off excess concrete. Form drain holes by pushing two dowels coated with petroleum jelly through the concrete.

2 Strip the outer form
After letting the concrete set for at least 18 hours, unscrew and disassemble the outer form (left, centre). Grab and twist out the dowels with pliers.

3 Pull the inner form
Remove the screws driven through the bottom of the mounting board and into the inner form. Tip the planter over and pull out the inner form (left, bottom). After the concrete has cured for 24 hours, apply a liberal coat of clear masonry sealer to the entire planter. Once the sealer cures, you’re ready to plant!

Glossary: Oculus
In architecture, the Latin word for “eye” describes circular windows, skylights and other openings, such as the hole in the top of the dome of the Pantheon in Rome. Specific to 17th-century Baroque architecture, oculus and oeil-de-boeuf (French for “bull’s-eye”) are used interchangeably.