Concrete Planter

Length of Project:
Project theme:
Suitable for grades:
Tools & Materials
Material List
  • found objects for molds (plastic, aluminum, or tetrapak are best)
  • dry concrete mix, Quickrete or similar
  • water
  • vegetable oil (also, spray-on cooking oil works well for this)
  • sandpaper 100 grit
  • Optional

  • acrylic paint
Tool list
  • safety glasses
  • work gloves
  • dust mask
  • measuring tape
  • felt pen
  • cup measure
  • mixing spoon
  • 15mL Tablespoon measure
  • ~3 cups of small pebbles or similar
  • bucket to mix concrete in
  • Optional

  • utility knife or scissors
  • paint brush
Procedure

    SAFETY NOTES:

  1. Be sure to wear safety glasses, gloves, and a dust mask while working with concrete, as both the dust and the wet concrete can be irritating to your eyes, skin, and lungs. This is an ideal project to do outside if you can.
  2. GETTING STARTED

  3. Choose two drink or food containers to use to make your mold: the larger one will be the outside, and the smaller one will fit inside to make the space for the soil. Make sure that there is at least 1" of space between the two containers all around so the concrete layer will be thick and strong enough. Look for containers that don't have bulges or flares that will make them difficult to remove from the concrete once it's hardened.
  4. Calculate how much concrete you will need to mix:

  5. Hold your containers in place (small inside big) while a helper pours water into the space between them until the water takes the shape you want your planter to be. Draw a line with felt pen on the outside of the small container where the water line was when you were happy with the shape.
  6. Pour this water off slowly, using your measuring cup to count how many cups of water you pour out of the big container. Round UP to the nearest cup, then write this number down beside the words "cups of dry concrete".
  7. Multiply the number from the last step by 3, then write your answer down beside the words "tablespoons of water".
  8. Mix your concrete

  9. Right before you begin your concrete mixing, spray or wipe the inside of your big container, and the outside of your little container, with cooking oil. This will help you loosen them off when the concrete has set.
  10. Put on your safety glasses, gloves, and dust mask.
  11. Scoop your dry concrete mix into your mixing bucket according to the amount you noted in step 4.
  12. Use a mixing spoon to make a little well in the middle of the dry concrete, then add the amount of water you calculated in step 5 using a tablespoon measure.
  13. Gently stir the concrete with the mixing spoon, making sure you scoop the bottom thoroughly until there are no more pockets of dry concrete. It should be the consistency of thick oatmeal.
  14. Pour the concrete from the mixing bucket into your big container.
  15. Tap out any trapped bubbles by dropping your container (right side up) from about 1cm repeatedly for a minute or so. You can also tap the sides of your container with your spoon or your hand.
  16. Push your smaller container into the surface of the concrete up to the line. Fill it with some pebbles so it stays in place.
  17. Let your concrete set in a cool, damp place, out of direct sun, for at least 24 hours.
  18. Wearing gloves, gently remove the containers from the concrete. If they don't peel away easily, ask an adult to help you cut them away with a utility knife or scissors.
  19. Put on your safety glasses, gloves, and dust mask again, and sand your planter with sandpaper to remove any rough edges.
  20. Decorate your planter by adding acrylic paints, if you choose.
  21. Add some soil and a plant, and place it on a sunny window ledge where you can admire your work!
Extension Challenges
  1. Add liquid cement colour to your water before mixing your concrete.
  2. Does your final product have small air holes, or "honeycombing" on the sides? On the jobsite, concrete finishers fill these holes with grout to make a smooth finish. You may choose to leave the holes in your planter because you like the texture, or you could use pre-mixed tile grout to fill them before painting.
  3. Build a form using wood and duplex nails, and spray the inside with cooking oil. Mix your concrete in a bucket, then place it in your wood form. Push a container in the top to make the interior space for your soil.
  4. Design and build a form using Lego blocks, making sure any of the blocks that will touch the concrete are flat (not the nubbly surface). Spray the inside of your mold with cooking oil to help it separate from the concrete.
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