Fabulous Fake Concrete Geodes




About: Welcome! Pleased to meet you, I am Barb; a Maker. I have been making things AND explaining how to make things for as long as I can remember. I was all about DIY before it was a popular term. I absolutely lov...

Remember collecting those shiny stones as a child?! They just seemed so precious. Well, now as a grownup you can challenge ‘Mother Nature’ by making your own with this Fabulous Fake Concrete Geode tutorial. No wimpy stuff here, the feel of real stone with this unique use of concrete. Check out my way of using easily found materials to get some super ‘bling’ in your life… Make them as big as you like!

Step 1:

During all my ‘concreting’ I have discovered some great characteristics of this RapidSet Cementall. That will be perfect in this tutorial. It's a quick setting mix that yields very strong results in a very short time.

Materials for the Casting:

  • RapidSet Cementall & Dust Mask
  • Reinforcing Fibres
  • Water
  • Container to mix in and mixing utensils (tongue depressors or like)
  • Smooth Plastic (plexiglass, CD case, or any flat shiny surface)
  • plastic bags/wrap/tape

Step 2:

These geodes can be made in 2 versions. As a ‘Slice’ or as a ‘Hollow’ Geode.

To Make the Geode Slices:

To make the slices you will need to ‘sandwich the concrete between some sheets of shiny plastic. I discovered that this concrete yields a super smooth shiny finish if it is poured on a smooth surface. Be creative, even CD covers could work. I used some old floor protector mat pieces as plexiglass is expensive. Do not use glass as when you put pressure on it you will break it (ask me how I know)
To give it a bit of extra reinforcement, I added a bit of fibres (but it could work without it). I have been impressed at the strength of this concrete, even as thin as 1/8″. RapidSet also mixes slightly different as it absorbs the water quite quickly and I usually need to add more mix. It acts differently than Quikcrete. RapidSet Cementall has a plasticity to it and sets really quickly with only a few minutes (less than 10 minutes) of working time so be prepared.

Mix a slightly thicker; less runny version of this mix. You want to make a rough ‘ring’ of concrete on the plastic. Push it to keep the shape.

To facilitate the attachment later of a stand; add a straw into the top and bottom. Make sure it is hidden in the concrete.

Once you have the ring about the size you like (make it random shaped as nature is not perfect) place another sheet of plastic on top and wriggle it to flatten. Do not flatten too much! It should be 3/16″ or a bit thicker. If it is very large; thicker is better. Mine are about 8″ or so. The edges SHOULD be quite rough, like stone. Another great thing; this concrete sets in 1 hour!

To Make the Hollow Geodes:

Make a ‘lump’ out of some plastic bags or wet paper towels and wrap in plastic. Add tape to keep it secure. Place the lump on the on the plastic and cover with concrete. Mound it and keep it rough to look like stone. You can sprinkle some sand if you like to add texture. There you go, the ‘hard’ work is done. I love how they look like a slice of stone!

Step 3:

To Add the Finishing touches:

You will need:

The Layers:

If there are any fibres sticking out, you can singe them off with a lighter. Take some inspiration from some images of geodes. Keep it simple; it’s all about the layers. Some are ‘curvy’, some are ‘squiggly’, there are no rules. Nature is quiet random, so have fun with it. I liken it to doodling, quite relaxing…

Work light to dark or back and forth. Add some metallics for fun; you are in charge here. The outer edge should look like stone so a thin layer of antiquing will do that. The reason I prefer acrylic inks is that they are highly pigmented. Inks provide a lot of colour without the ‘thickness’ that comes with cheap paint and they are permanent when dry so sealing isn’t a problem. Being a bit more expensive is worth it in the long run.

Once you get the hang of the painting ‘layers’ you will be amazed! Add a few in gold or silver… Squiggle away… The metallics catch the light so nicely!

Step 4:

Making The Crystals:

So, before you think I am crazy there is a reason for this! I had been thinking for so long about how to make ‘crystals’. Growing crystals is not easy and they don’t always last. Soooo, I did what I usually do, make them!
I threw a bunch of these flat glass beads in a cast iron pan (lid on just in case) and heated for a few minutes.

My idea is to shatter these. So slide them from the pan into some ice water and they will internally crack. Cool! Baked glass; who knew?!

I like the way that the glass breaks with a bit of a tap of a hammer. Just don’t do it on the table or on the new kitchen counter! No, I didn’t… btw. If you broke normal glass it would be too sharp and pointy. So there you have the crystals that you will need to finish the DIY Giant Concrete Geodes and since they are glass, they will not dissolve…

Step 5:

Attaching The Crystals:

The whole attraction to geodes is the crystal interiors!

To adhere the crystals I tried a few different methods.
The most permanent way is to use epoxy (a 2-part glue that can cure in 5 minutes) but it will flow to places that you may not want. If you use epoxy you can put a piece of plastic that has been greased with vaseline on the back to allow removal once the epoxy has set.

Clear silicone will adhere the glass in a more rubbery way. It is supposed to be clear but is still a bit cloudy once dry. It is quoted as being waterproof however.

The quickest and easiest method is with hot glue. It allows you to set the stones where you like and build up quickly. Ask your self how permanent or much wear it will get. I intend to use them as decor so that will be adequate for me.

Build up the ‘crystals’ and add stones to make it look authentic. Blue glass with a bit of clear mixed in. Layer and fill but keep within the shape. The colour options are endless… To give them some shine you can add a layer of gloss medium. The metallics will catch the light so I like the shimmer of matt against shine. The concrete has quite a shiny finish on it’s own. That is one huge geode!

Step 6:

Insert a piece of wire (coat hanger) into the slice and base (check here to see how to build the base), adhere with glue. Baffle your friends! Make a collection!

Check out my site for more unique DIY projects that you won't find anywhere else. if you are new to concrete crafting check my tips.

So many great concrete projects... so little time!

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    14 Discussions


    4 months ago

    Recently saw this on Instagram. And was a thinking that I for sure want to make this one up glad to see u on indtructables:)


    Question 4 months ago on Step 2

    Your items are impressive. I wonder if automobile broken glass would work for the geode? Windshields break up into tiny pieces. I need my windshield replaced because it is cracked. Maybe I should save it and crack it up, store the pieces in a jar for later ART projects?

    1 answer

    Reply 4 months ago

    Since making these and even making more designs I have been on the hunt for the glass. You can use the windshield glass. I love the way it has little shapes and is not so sharp. I have a windshield 'guy' saving glass for me too. Did you know that windshields are 2 layers of glass with plastic in the middle?! There is also glass stones sold for fireplaces called fire glass. They are very pretty in different colours but can be quite pricey. The bus shelters here are a very thick glass and sometimes get broken so I keep my eye for those too... I can never have enough... make planters too!


    4 months ago

    Excellent. Plan to copy your idea. Howevr error when downlading the instructable.


    4 months ago on Step 6

    I just LOVE these! So Clever too. You would sell many of these at a craft show. Seriously. Well Done.

    1 reply

    Reply 4 months ago

    Thanks! Funny you should say that; I did go to a show about gems and there was a woman who was selling MY GEODES! When I nonchalantly made conversation about how she learnt it she figured out I was the one that designed them and she recognized me from my site. She has made many and some very huge ones. My only comment was that they looked somewhat 'fake' since the colors were so strong and saturated.


    4 months ago

    These are quite authentic looking...nice work! I voted for you! These would make a tremendously cool "feature wall" somewhere if one was inclined to put in that much work...or perhaps a resin sealed counter top...lots of possible applications waiting to be discovered!

    1 reply

    Reply 4 months ago

    Oh yes, my mind runs rampant as I make things and dream up more possibilities! The problem I get so many projects on the go that I don't have time to make a post...


    5 months ago

    Another great tutorial, I've always loved 'shiny shuttered concrete' !


    Reply 5 months ago

    That could be quite amazing! I am sure there are some challenges to having a strong finish for wear and the crystal edges...


    Reply 5 months ago

    Resin! :)
    I’ve been planning on resin flooring as is, and working on design ideas to go underneath. This is perfect!