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When I get an idea in my head I am so determined to make it work that I sometimes wonder if it will ‘kill’ me first! This was one of those ideas… I was on a mission to create another orb design; but not just a typical one, I have to be super unique! With the help of a volcano and ingenious thinking see how I managed to make these DIY Rock and Concrete Orbs work.

The Spherical Mold:

I wanted to create a casting from the inside of a mold, a sphere of course. Well, if you have ever tried to find a perfect sphere it’s not easy! I bought ball after ball and cut them open. Nope, not smooth enough. Basket balls have wierd seam lines inside. Other balls shrink to a limp skin. Plastic orbs are next to impossible to find… Soooo, I had to do what I usually do; make one.

My ‘Go-To’ method of making a mold always seems to save me.

What you need to make DIY Rock and Concrete Orbs

  • One box of corn starch
  • One tube of 100% Silicone Caulking
  • Old bowl
  • Gloves and good ventilation (super smelly stuff!)
  • Caulking gun, knife to cut it open
  • A smooth well inflated ball (cheap kids play-ball)

Have your ‘master’ ball ready by sitting on a bowl for stability.

Squeeze the entire tube into the bottom of the bowl that is well filled with the corn starch. The intention is to keep it suspended in the starch so that it does not start to stick on the sides. Keep it in one mass, tossing and working in more starch  so to get less and less sticky.

Try to keep a layer of starch between it and your fingers as well.

Turn and toss carefully incorporating more starch  and it will become less sticky.

After it absorbs more and more starch it will start to become moldable as it won’t stick to the fingers as much. This is so much like making a dough (I guess my years working at a bakery helped!).

Roll in your hands to make a ball of even consistency.

Flatten the ‘dough’ on a flat surface that has a dusting of corn starch to about 1/4″ thick.

The mix starts to set pretty quickly so immediately place it over your form ball and smooth it out. Do not worry about the edges or excess. I was aiming to have a good 1/2 of the ball or bit more covered.

It will usually set with in 30 minutes I find. When you you poke it and it feels like rubber then it is set. It popped off easily and I finally had my sphere mold. It is flexible but also keeps it’s shape well – perfect!

The Rock:

As you know by now, I love rock! It has to have some character, I’ve always marvelled at the way that lava rock is made, cooled lava from a real volcano. It is available as the internal rock for BBQ’s and also as a landscape type mulch. I used both types, but the bagged lava rock was larger and more colourful.

Which Concrete Mix to use:

I am always trying to get so much done (life of a blogger & maker) so I am happiest if I can use one of my quickset concrete mixes. I used the Quikrete Fastset Allcrete on this project but the Rapidset Cementall will also work here (it ends up lighter colour)

Both these mixes can work at various consistencies. I did try a few variations and the results were all great.

If you would rather not see the any of the stones in the final form you can mix a very fluid mix and let it run between the rocks that line the mold. If you want to see more of the rocks you can use it more as a thicker mortar and just have it between the rocks.

You should experiment… I did realize that it is strong and holds the rocks together even if there are some empty voids.

The Method:

This is not a perfection type of orb, it has a lot of character and will be quite unique. There is somewhat of an element of magic here as to how it turns out; but that is what makes it so refreshingly different.

The ingenious thing about a sphere is that you can work in partial portions. Gravity is something that will work against you so working in smaller sections is better.

Once one section is set (about 1 hour if it’s warm) you can move it up the side to then work another bottom section next to it.

Place that set section on one side and then add more in the bottom. Slightly mist the existing set concrete to have better adhesion.

Add rocks by letting the mix run in between or ‘mortar’ the individual rocks where you’d like them. You are in charge here.

You can continually adjust position to ‘fill’ as much of the form as you like after each addition is set. My vision in my mind was to resemble some type of ‘carved-out-of-rock’ orb. The hollow void will be great for the other ideas I have!

I love the flexibility of this mold! It does tend to stick but can be worked lose with a bit of manipulation. I do not really like the gunk that builds up when using a spray release like ‘Pam’.

The Reveal:

Once you pull it out of the mold you will be amazed… Isn’t that so interesting?! So many elements of design, form, texture, shape and colour! Yes, colour! You can add some concrete colour to the mix to have some variations of colour.

Ta-Da! So unique and a perfect accent to the natural landscape of a garden.

Each one will turn out with it’s own unique pattern.

The motto here; don’t give up, there will be some way of achieving what you want if you persevere!

Place these DIY Rock and Concrete Orbs in the garden or anywhere that needs a bit of natural interest. ‘But just wait to see what these will become… another vision has popped into my head! See part 2 here:

Happy concreting!

I'm an artist & I make things... all kinds of things.

This Post Has 45 Comments

  1. I have been trying to figure out how to achieve this effect and you nailed it! Thank you Thank you Thank you;-) Now off to try this piece of art.

  2. I have collected glass globes for a one time use.. just make sure you can get your hand inside to put in the cement/ rock. I love all the things that you do , especially the geode lamp.. haven’t gotten to do any of your ideas yet. We are building a new shop on the property so I can do projects…. Can’t wait to get some made …. I”ll share pictures We have been doing pendants… Mostly using combination of resin/ jewelry/ driftwood .I”ll send pictures another time.

  3. Love your concrete ideas. Living on a social security check but would love to try some concrete art while I can. I missed saving the one for trellises.

  4. I saw the comment by Rose Marie about the trellis and thought of the orb you made with fleece. You could use that like a trellis and grow ivy on it ! I have made an orb but not the fleece one yet. Love your work. I have several smiling rocks.

  5. Hi Barb this orbs look absolutely stunning. Impressive! Dont you perhaps have pictures of the process? Maybe I will manage better to try make them please.
    I will also have to search for the lava as I have never seen it in my country.

    1. I am not sure why you don’t see the umpteen pictures? See here and here. If you can’t find lava rock you could use other nicely textured rock, just dampen it so it does not suck all the moisture from the concrete. They sell lava rock to put in the bottom of gas BBQ’s here. Happy concreting!

  6. Hi Barb , just discovered your site . Love your work , love rocks, plants etc. I used to make plaster molds decades ago for several years. Eventually , I gave up the ceramic thing and moved on to something else. Im always interested in new ideas . I always garden in good weather and in cold weather I sew. We have a group of ladies at my church and we work all year to make lap robes for local nursing homes who care for folks with low incomes and give them for Christmas gifts . We deliver them the first wk of Dec.
    So , have a great day and keep up the great work . I subbed to your site so I wont forget.
    Pauline way down in Okla USA. .Just above Texas.

    1. It sounds like you get much satisfaction from making and it’s great that you can contribute so much to the ones who can use it! I have had my hands in so many different crafts and arts over the years as well. It is beneficial for me to be able to make cross references between different art forms. I have no shortage of ideas… Greetings from up here above the border!

  7. A-freaking-mazing! I am new to your blog but am working my way through it bit by bit. Your ideas have spurred so many new ones of my own! Art in its truest form. Thank you for sharing your creativity!

    1. Thanks! Yes, I am an artist more than a blogger… So great to get feedback, something that doesn’t happen when you work alone in your studio. I’m like a pingpong ball bouncing from one art form to another… Happy making!

  8. These are genius…I’d bet you could put some moss in at the bottom before topping with cement too…too fun!

  9. I am having SUCH FUN making your geode garden orbs! I’ve made 2 so far and plan to do another 3 tomorrow!!! They are so beautiful! I love how they turned out!

  10. I just found you on Hometalk, and I’m impressed! I’ve been a rockhound most of my life, but never did much with them. You’ve got great ideas! I’m dying to try the geode orbs!

  11. Bonjour, et voilà, j’ai le virus. Toutes ces possibilités, tous ces ratages qui peuvent devenir des réussites. Il y a un truc que je n’ai pas compris, c’est le déplacement de section, j’ai pourtant lu et relu, mais niet, Merci pour ces belles réalisations et surtout les tutos qui m’offrent l’opportunité de rêver à des formes, des cristaux, des pierres etc… bonne journée Nicole

  12. Hi Barb. I made a cement plantar. Even though I didn’t purposely make a delicate fringed edge that is what turned out. I love it! But I need to find a way to harden the edge so it doesn’t break. Can you offer some ideas please?


    1. You could add a reinforcing layer. Dampen the concrete that you want to add to and use the extra strong mix (Rapidset Cementall) Make sure it does not ‘steal’ all the water from the new mix or it will fall off. You can use a brush or palette knife. Good luck

  13. Step by step pictures would be SO helpful on your blog posts. I’ve read over quite a few but it just creates so many more questions lol. Thanks for sharing none the less.

    1. I would think that over 18 pictures with steps would be sufficient. Maybe your settings are not loading the images? Check it out. All of my posts have so many pictures of all the steps. ‘Hope you will see them!

    1. I don’t seal my concrete as it is never really permanent. They let water through and don’t hold any so I have not had any issues with them. And we have pretty harsh winters here in Canada.

  14. Hi Barb, your ideas are so amazing and you inspiring! I tried making the silicone and corn starch ball mold this morning…but i think my box of corn starch was bigger than yours bc the dough cracked and crumbled. How many ounces was the box you used? Or hap many cups? TY!

    1. I do not measure, but rather work it until it becomes a good mix; like working with flour. Are you sure it was 100% silicone? It may have been acrylic caulking to crumble.

  15. Hi Barb,
    I started making a mold, completed the steps through forming the ‘dough” onto the ball and letting it sit overnight just to be sure it would have to complete cure. When I peeled it off, it was stiff soft and very sticky on the ball. What went wrong?

    1. I think you are making a silicone mold of the half sphere? If so, I think that you possibly did not use 100% silicone. An acrylic caulking will not work in this case. The silicone and corn starch mix actually almost sets/cures too fast.

  16. Adoro internet per cose come queste avere la possibilità di vedere e imparare a fare cose fantastiche come fai tu anche dal Italia ho frequentato l l’accademia di belle arti a Firenze ma certe cose così creative non si insegnano a scuola grazie di aver condiviso la tua conoscenza

    1. “I love the internet for things like this to have the opportunity to see and learn how to do fantastic things like you do even from Italy I attended the academy of fine arts in Florence but some such creative things are not taught in school thanks for sharing yours knowledge”

      Yes, I agree. I learn the best just by trying ideas in my head. Sometimes it takes a few tries but that’s the fun!

  17. Hi Barb, love your site, which I recently discovered. I made an attempt at your silicone mold, intent on trying the geode balls. Problem came when I draped the silicone and cornstarch dough over the ball. The weight of the dough pulled it apart, so I ended up with thin and torn sections.. I definitely used 100% silicone. Should I have added more cornstarch? I had a 300ml tube of silicone and used most of a 500g pack of cornstarch. There is no indication of it firming up, even after a couple of hours. Thanks for your advice.

    1. That is strange. I have read some issues about the silicone II (2) not getting stiff. I work the mix until it gets to the stage where it doesn’t stick to my hands anymore it’s pretty dense (stiffer than play dough) and it stays where I put it. It is also well mixed at that point. I have to work fast to get it over the form. Was it still sticky? The corn starch lets the mixture cure throughout, so maybe it needed more. If your’s eventually cures you could add a layer. Whenever I am in doubt I try small test mixes. I was ‘fighting’ with some plaster the other day… I think it was just too humid… 🤷🏻‍♀️

      1. Hi Barb. Thanks for your reply. It did set overnight, but because I had to fight with it to keep it on the ball and ended up pressing it all into a bowl, it’s not the shape I was looking for. I’ll try again and work it a bit more next time.

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