Small reusable rounded bottom planter mold

I wanted a small, simple shaped concrete planter and I was inspired by some great 3d printed planter mold designs out there.

This was modeled from scratch and prints without supports. I've reused the same mold multiple times without problems using a concrete patching mix. The finished product is about 3" wide by 3.25" tall (~75x80mm).

What you need
-The 3d printed parts; 1 inside, 2 bottoms, 2 sides.
-Some tape, I used electrical because it has some flex
-A balloon
-Your concrete mix. I used a concrete for patching so the aggregate was small. I'm sure a plaster would work as well. I would suggest avoiding typical concrete with large chunks of aggregate.

How to
-Stretch the balloon over the inside plug and work any air bubbles out.
-Assemble the 3d printed parts and tightly wrap with tape
-Mix your concrete according to the manufacturer. Be sure to use all suggested safety equipment.
-Add the concrete to the mold and tap the mold on a scrap work surface to vibrate bubbles loose.
-Wait for it to cure according to the manufacturer. I waited about 24 hours.
-Very carefully remove the mold - it will still be very brittle at this point. Cut away the balloon and the plug should slide out. If it feels stuck you can apply a little bit of force using the square hole on the inside plug.
-Wait for it to fully cure for a few more days and sand to the desired finish.
-Apply any cement sealer or paints you would like.