This is my first try at creating a mold for a concrete pot. It is almost the largest mold you can make with the Prusa I3.

You need to use a mold release. You can get special concrete mold release, or you can use most of a can of non-stick cooking spray. Also, read the Print instructions!

Print instructions

For where the screws hold together, you will need extra perimeters for strength.

I used M3 screw inserts to hold the two parts together.

Also, print this slowly. It is a large print, and layers separation will happen. The slower you print, the more time the layers can melt together.

When preparing the mold for concrete, get some sandpaper and smooth out the inside of the print.  Right before pouring in the concrete spray the inside with non-stick cooking spray so it will come apart when it is done.

When you have poured the concrete, shake the mold for about 10-15 minutes this will help remove air bubbles.

I designed this object. Feel free to use it however you want.