◆ Concrete

Tapered square concrete planter mold

A tapered square planter, 95 mm at the rim and 88 mm tall, to cast in concrete. A silicone mold kit from printed parts.

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3D render of the tapered square planter master fused on its printed charcoal base, between the orange and blue shell halves, with the charcoal clamps behind
Concrete ~365 g Pro early access

A tapered square planter 95 mm across at the rim and 72 mm at the foot, 88 mm tall, with corners rounded to 9 mm and a small chamfer round the rim: the plain modern pot that suits any shelf. The well follows the square with an even 8 mm wall over a 12 mm floor, and a 10 mm drainage hole runs through the middle.

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Made with the hugging-shell mode of our silicone mold maker, which the tool itself suggests for this standing pot: the silicone follows the square about 10 mm out instead of filling a box, so the mold takes about 1060 ml. Print the base with the planter fused onto it, the two shell halves and the six clamps, and pour into the open top. The silicone fills the well as it rises and becomes the core, with a pin that forms the drainage hole.

Cast it in grey concrete, white Jesmonite or a charcoal-tinted cement, and seal it before it meets wet soil. The zip carries every printed part, the planter master as its own STL, the tool's own print-settings sheet and a recipe file for the generator.

Shown as a 3D render of the printed mold parts pulled apart around the master, not a photo.

What you need

4
  • About 1130 ml of silicone (mix it in one batch)
  • Concrete, Jesmonite or a fine cement mix: each cast is 223 ml, about 491 g in concrete
  • Tape or a hot glue gun for the shell seams
  • Fine sandpaper, a concrete sealer and felt pads

How to cast it

7

  1. Print the base, which has the master already fused onto it, the two shell halves and the six clamps (all six are in clamps.stl). No supports.

  2. Stand the base plate on the table, set each shell half down a few centimetres out from it and slide it in until the ridge round the plate sits in the groove at its foot. Push the six clamps over the seams: the shells cannot lift after that, and the ridge seals the bottom.

  3. Tape the outside seams or run a bead of hot glue along them, because silicone finds every gap.

  4. Mix 1130 ml of silicone in one batch, pour it into the open top in a thin stream, and fill level with the rim. It fills the well as it rises and becomes the core.

  5. Once it has cured, take the clamps off, slide each shell half straight out and peel the silicone off the master the way the last step describes. That silicone is your mold: a skin with the core standing inside it.

  6. Turn the silicone over and set it back in the shell to keep its shape: the opening is the foot of the planter, with the drainage pin on the tip of the core. Pour a fluid concrete or Jesmonite slowly down one side, tap the shell for a minute to raise the air, and strike the foot flat, wiping the pin tip clean.

  7. Demold after a day: peel the silicone skin back off the sides from the open foot. The pot is wider at the rim, so the skin has to stretch; a slit down one corner makes it easy, and the printed shell holds it shut again. Then lift the planter off the core. Sand the foot flat and seal it.

Print details

12 h 10 minPrint time
~365 gFilament
9Printed parts
141 × 140 × 105 mmSize (W x D x H)
All print details
Print details
Cast materialConcrete
Printed parts9
Size (W x D x H)141 x 140 x 105 mm
Print bed needed140 x 113 mm, 105 mm tall
Filament~365 g
Layer height0.2 mm
Infill15%
SupportsNot needed
DownloadZIP: 9 printed parts in 4 STL files + planter master (STL) + print sheet + recipe
Added2026-09-26

Pro early access until October 26, 2026, then free with any account.

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Made with the free Silicone mold maker generator. Upload your own model and get the same kind of mold built around it, in your browser.

Free for personal use. Selling the pieces you cast needs a commercial licence (Pro or Founder); passing on the file itself is not permitted on any plan. Full terms.

New to casting? Read the silicone mold maker guide.

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Questions about this design

What size plant fits the tapered square concrete planter?

The well is 79 mm square at the rim and about 60 mm at the floor, 76 mm deep, so a plant from a 7 cm nursery pot goes straight in, or the nursery pot itself drops inside as a cover pot. Put a layer of grit over the drainage hole before the soil.

Why is the tapered square concrete planter made in a hugging shell?

Because it stands taller than it is wide, and the tool itself suggests the shell for that: the silicone follows the square about 10 mm out instead of filling a whole box, so the mold takes about 1060 ml. The flexible skin also peels off the tapered sides, where a thick block would have to be cut open.

How do I keep the corners of the tapered square concrete planter from chipping?

They are already rounded to 9 mm, which is what stops most chips. Demold after a full day rather than a few hours, lift the pot by its body rather than the rim, and let it cure for a week before it takes a heavy plant. A coat of concrete sealer hardens the surface too.

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