Large Holey Concrete Voronoi Orb

Voronoi shapes are quite interesting and lend themselves well to the use of concrete. Why not combine Voronoi shapes into the structure of a sphere; a large Holey Concrete Voronoi Orb! Let me enlighten you…

What is Voronoi?

‘A Voronoi diagram is a special kind of decomposition of a metric space, determined by distances to a specified family of objects (subsets) in the space’ as explained by J Smallwood. Look closely as you will see many small odd shapes that come together to create the leaf cell pattern. You know how much I love taking inspiration from nature; and Voronoi in nature is amazing! It’s quite complicated to figure out the geometry but my design is quite simple.

The Shaping:

Before you get ahead of yourself you need to get the shape ready. I’d rather use a deflatable beach ball as balloons can burst and not be so round. When making concrete orbs often covering a ball is difficult since the concrete slides off so here we use a wrapping of poly-twine in ‘Voronoi’ random shapes as an aid for reinforcement. Also add some drywall mess to help to adhere to the ball since it has slight stickiness. Tie and twist as you wrap so that the string does not slide off.

The Concrete Mix

I get many questions about which concrete to use and this mix is my favourite (no affiliation with company) It works easily and cures/hardens fast enough to allow continuous working. Do be aware of temperature and other factors that may dry the mix too fast and always be safe with gloves and dust mask. If you are new to concrete crafting then you may want to check here for some tips.

This mix acts somewhat differently than other mixes but also hardens to a stronger finish. The amount of water needed tends to be less than other mixes as it’s absorbed quickly to make a more ‘plastic-like’ mix. The company recommends adding mix to water; and after using it many times I understand why now; who reads instructions?!

This very part is important; as the consistency of the mix makes all the difference when molding by hand. If you allow the mix to sit for about 30 seconds it will thicken already and become more like a moldable clay. Adjust of it’s too stiff or too runny and only mix small quantities as it will harden before you can use it; I mix about 300ml or so.

Let’s go!

Here’s the fun part… getting a bit messy! As the ball is very stable on a bucket start at the top to keep the weight distributed or it will roll (don’t ask…) Work over a ‘string line’ and across others… Shape the concrete into rolls in your hand and apply, smoothing with your fingers. Since this is a plastic ball the concrete does not stick to it so I do not use any release agent.

Maybe I’m secretly wanting to be a ceramic artist again without the kiln?! This is much like working with clay but a tad quicker. Shape & smooth, add a line, shape and smooth… Slightly rotate the ball as you work downwards. The lacework is about 1/2″ thick

An old brush and water will help take away any lumps and curve the shapes. There are no rules here; and no perfection expected; only that it has enough structure to NOT fall apart. Divide up the larger ‘holes’ into smaller ‘cells’. Once the finished areas are cured/hardened the sphere may be turned to work on the other half

Doodling is very similar; just add as you feel like & keep turning and looking… Use you intuition where it needs more shapes. When adding to areas that are somewhat dry/cured makes sure to spray with water so no cracks happen. Additional concrete can be added later to the concrete orbs if the first layer is well wetted so it does not ‘steal’ the moisture from the new layer.


Concrete likes to be damp when curing. Spray it with water often to build it’s strength and have even curing. This mix will cure to a very strong finish in about 1 hour but you can always give it a bit longer.

Why waste when you can reuse? Deflate the beach ball and pull out of the largest hole of the concrete orb.

Winters in Canada can be crazy but this concrete orb does not have any places to catch water so it fairs really well all year long outside. Ivy will grow through the concrete orbs and it will accent the natural shapes of garden much nicer than the artificial manmade shapes. My theory is that a garden should be about the the natural elements and anything else should follow suit…

Thanks for joining me in my garden and my crazy concrete addiction… IF you want to make more concrete like the large face or other orbs or eggs … concrete on.

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  1. Dear Barb,
    Thank you very much for the inspiration and instructions on how to make this wonderful orbs!
    We bought the concrete mix you recommended and tried to follow all your steps. The concrete started cracking in some places, while drying. We did mist it in the process of drying. The thickness of the concrete layer was a bit less than 1/2 inch.
    Could this be the problem?
    Any other ideas what did we do wrong to cause these cracks?
    Thank you so much.

    1. That rapidset cementall can be really strong. Cracking can mean that it is shrinking and pulling apart. It may be from drying too quickly or too much moisture. If it is only in a few places you can well wet those sections and add a bit more. It adheres well as long as the older concrete does not ‘steal’ the moisture from the new. I ‘added when I made the chair. There is some trouble-shooting here Don’t despair, it’s a bit of a magical mix and therefore it takes a bit of practice with it…

  2. Concrete creates heat and may inflate you beach ball as you work on it. This can be fun or frustrating. It may want to float away or spin on it’s own.

    1. Yes, you are right; it does generate heat. I have used inflatables for many years and have not seen any evidence of extra inflation. I do work in the shade and the amount of concrete (thickness) is often not that much, so perhaps it dissipates quite quickly. This voronoi version is especially not very solid to hold the heat. I have sometimes noticed some deflation when it gets a bit colder at night. I also wonder if the fast-setting mixes have a somewhat accelerated heat-up and cool cycle… I did change from using balloons as I was not that happy when one would fail/pop but it wasn’t from inflating.