After Octavian conquered Egypt in 30 B.C.E., he brought back the towering obelisks of the pharaohs as trophies and displayed them in the streets of Rome. Although it may be beyond your means to cast a 40-foot obelisk, you can make a miniature version for your home or garden that will be just as impressive to your neighbors'. You can even decorate your concrete obelisk with Egyptian hieroglyphs.
Prepping the Mold
Mark the vertical center line on opposite sides of your solid plaster block. Measure and mark the width of your base with a pencil and ruler. Use a compass and pencil to trace converging lines -- from each side of the base -- at 35-degree angles. Make identical lines on both sides of the block.
Saw along the lines with your handsaw, starting from the top of the plaster block. Ensure that your blade follows the line on both sides of the plaster block. Wear a dust mask and safety goggles while sawing the plaster. Discard the excess plaster. Repeat the last step on the remaining sides.
Measure and mark a horizontal line near the top that is one-tenth of the vertical length of the block. Draw lines from this point that converge on the vertical center of the obelisk. Cut the excess with your handsaw. This will form the top, or pyramidion of the obelisk.
Carve Egyptian hieroglyphs into the plaster, if desired, with your Dremel tool. Pencil these designs onto the plaster obelisk and carve shallow grooves with your Dremel tool.
Brush latex mold compound onto the plaster obelisk, covering all parts but the base. Use a heat gun to speed the process. Apply a total of six layers of latex mold compound to the obelisk. Add another layer of latex compound and wrap the obelisk with gauze. Apply a final layer of latex and allow the object to dry overnight.
Remove the plaster obelisk from the mold and discard. You may need to peel down the first few centimeters of the mold and grab the base of the plaster obelisk. Attempt to shake it free of the mold. This may require a few attempts.
Spray the inside of the latex mold with WD-40. This will act as a release agent, allowing the cured concrete to free itself from the mold.
Concrete Mix and Pour
Mix one part Portland concrete mix with three parts dampened sand in a large bucket. The amount of concrete will vary, depending on the size of your obelisk, but ensure that the ratios of the mixture are exact. Add water until the mixture is thick but not runny. Wear your dust mask, safety goggles and gloves during this process.
Pour the concrete mixture into your latex mold. You may have to prop the mold to remain upright as the concrete cures.
Pack the top of the mold with your hands to remove air bubbles from the concrete.
Allow the concrete to harden before freeing it from the latex mold.
Spray or soak the concrete obelisk for three consecutive to allow the concrete to bond properly. Cover the concrete obelisk with a plastic tarp each night. Allow the concrete obelisk to dry for two days before displaying it.