Introduction: Triangular Geometric Plant Holder

The following instructable will teach how to create a mould and core with high impact polystyrene, for a small plaster succulent or sprout plant holder.



- high impact polystyrene (HIPS)

- ruler

- pen

- scissors

- cutting blade

- tape


- plaster (water + plaster powder)

- bucket

- spatula


- sanding board

- cork block

- sandpaper of different roughnesses

Step 1: Drawing the Mould/Core

Using a black pen and ruler, draw the mould and cores for the holder on a sheet of high impact polystyrene. (Usage of other alternative materials such as polypropylene may change parts of the process and outcome.)


For the mould, I used 8cm equilateral triangle faces, drawing one first as a template to trace the others. I traced it to create seven total faces, four connected as one pyramid shape, and three separately. (You will see later how to arrange them when creating the 3D mould.)


For the core, I drew a triangle pyramid (three on the bottom, one on top of the centre) shape using 5cm equilateral triangles. (The net for the core is all one piece.)

Step 2: Cutting/Preparing the Mould/Core

Using scissors, cut out the shapes of both the mould and core, making sure to keep the main triangular sections as single pieces. Score the edges of these sections (as shown) using a cutting blade to make them easier to fold up.

Make sure to do this to both mould and core nets, making sure not to press too hard otherwise snapping may occur. In this case, simply tape the edges back together.

Step 3: Assembling the Mould/Core

After cutting and scoring the nets, tape the faces together (layout for mould shown in previous step) using tape to produce the shapes shown in the photo.

For the mould, it is recommended that the shiny side of the high impact polystyrene is on the inside (to make plaster smoother and easier to remove), while the tape remains mostly on the outside (to reduce marks on the plaster). Vice versa for the core, where the shiny side should be on the outside and tape on the inside.

However the most important thing is that all edges are sealed tightly to avoid any plaster leakage.

Step 4: Preparing the Plaster

Prepare the plaster to be used based on the specific instructions from your brand.

For my pot, I used a 2:3 ratio of water to plaster, using 135ml yoghurt cups to measure. The most important thing is the consistency of the plaster - it should not be stiff and clumpy, but should not be too liquidy as well. A nice thick plaster is ideal, as this will dry the best and produce the best texture.

Make sure to mix the plaster thoroughly with a spatula in its container (I used an old paint bucket) before pouring, for a smoother texture.

Step 5: Pouring the Plaster

Once the plaster is prepared, pour it into the mould. Leave a few centimetres of space at the top (don't pour too much or it will overflow).

Insert the core into the centre of the mould and leave for a few minutes to let the plaster harden a bit. Then secure into place with tape - add enough tape until it can hold its place by itself, but make sure not to add too much tape or tape too aggressively, as this can alter the shape of the mould.

Leave the mould to dry for an hour at minimum, although a longer period of time would be a safer option.

Step 6: Sanding the Holder

Remove the mould and core by hand, using scissors or a blade. (Be careful not to cut/chip the plaster).

After that, sand the plaster with the sanding block before moving to the sandpaper, from roughest to smoothest.

This should remove any roughness and bubbles within the plaster and give a smoother effect. (However if the plaster is already smooth, sanding may be unnecessary as this can take away how shiny/polished it looks.)

Step 7: Done!

And you're done! You can use this holder for small succulents and sprouts and customise it however you like with paint or other designs - after all, you made it all yourself!