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DIY Giant Concrete Geode

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 DIY Giant Concrete Geode tutorial. No wimpy stuff here, 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…

During all my ‘concreting’ I have discovered some great characteristics of this RapidSet Cementall that will aid in this tutorial.

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
  • cocktail straws
  • Vinyl tiles (xacto knife, straight edge/ruler)

Step 1: The Concrete Forms:

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

To make the ‘Slice’ Geodes:

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 one 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 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.

All set to be great DIY Giant Concrete Geodes! 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!

To make the square bases:

If you want to make a stand for your ‘slice’ you will need a base. My favourite material for shape making is the vinyl tile as it cuts easily and holds up to multiple uses. I made my blocks 3.5″ wide but you can use what size you like

A simple block shape is folded up and tape on 2 corners.

The other 2 corners will be opened so I made tabs to secure with clips (less taping)

Mix up some and insert a straw (end taped shut) into the middle and secure.

Awesome simple square bases (sponged with a bit of paint)

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!

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…

Marbles will also break, and you will have larger and smaller pieces.

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…

That is one huge geode!

The back side gets a bit of antiquing.

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.

For my ‘blue’ room with a stand made of copper wire.

Insert a piece of wire (coat hanger) into the slice and base, adhere with glue. Baffle your friends!

So many options.

They go great with the rustic concrete bowls! Don’t blame me if you catch yourself staring at them for too long… Bravo!

barbmaker

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

This Post Has 69 Comments
  1. These are VERY creative! Love the broken marbles and gems, possibilities are endless! Got my creative juices flowing! BTW! I was wondering if liquid resin would work in placing the glass “crystals” inside the “geode”. It dries super clear and probably adds more sparkle! Just a thought!

    1. Funny you should mention that! The first center I made was with clear resin. The problem was I had to make the shape first. The glass that was inside the resin lost most of it’s sparkle. If you had intended on just using it to adhere, you would have to use a quick set one or it would be hard to work with. Essentially the 5 minute epoxy is similar. Perhaps a combination is best. Spot glue with hot glue to hold in place and then drizzle with epoxy for a strong hold. I’ve got some more uses up my sleeve so I ill try that…

      1. I too am an artist but maybe a bit of a perfectionist lol!! I am definitely gonna try to attempt this DIY geode because it looks absolutely gorgeous!! My only thing is, I would like to have had pictures of each step during the process, to have the visual of what shape/look I’m trying to achieve. Otherwise, it’s definitely worth trying!!

        1. I am not sure what the problem is as there are a ‘gazillion’ pictures of all the steps on my post. Maybe you did not wait to let them all to load. Yes, there are ads (need some support for the work) but many many steps. Maybe a computer is better to view on as well.

          1. Hi Barb,

            I love your project and want to make one as well, but like Paul expetienced, there are no pictures of your work on the pin. At first it was other ads (didn’t change) and now it’s just a picture of clouds in each space. Not sure if it’s something the site has done or what. Hoping to see the steps as it does help me when I do a project.
            Thanks again for sharing such beautiful work, this exactly what I had in mind when wanting to make a geode 🙂

          2. That is exactly what I was going to say. You have tons of step by step photos. You are sharing a gift with us. You should be commended! You are a gifted artist and you have just “given away” a beautiful technique. Thank you my lady

          3. That is very kind. I do wonder about this endeavour often. I ‘do’ and then figure out how to do it better next time… Otherwise I’d be taking courses forever… Happy ‘Making’!

  2. Your work is so very inspiring. Thank you so very much for being generous in your sharing. You have moved me from the “I wonder” stage to the supply gathering, doing stage. Thank you so very , very much. Such beautiful work you do.

    1. Wow, thanks for the nice words. I’m glad that the countless hours are making an impression on someone. I’d say one of the biggest challenges I see people have is the lack of believing in themselves…

      Whenever I try a new media for the first time I try tiny tests to see how it works before I use up a large supply… walk before running…

  3. This is exactly what I have been looking for! I love the Amethyst geode bookends but the prices have gone way out of my budget. This may be my new DIY Christmas gift for those hard-to-buy-for people as well as myself. You are just amazing and thank you for sharing this step by step!

    1. Thanks, It’s been a quite a process to get there! I am sure you’d also like the lamp! With different colours and glass the possibilities are endless! I have some more versions of it as well…

    1. I am not quite sure what you are referring to, but I used some gold acrylic paint, and also some ochre colour glass, and some small gold colour gravel. Really, whatever matches your intent can work. I do stay away from plastics though. Some aquariu stores have great stones, I even saw some large chunks of glass at “Michaels”. They are pretty forgiving at nature is not perfect either!

  4. I love this idea! I bet you could use broken safety glass too! Since it breaks in squares, it would be convincing crystals! Thanks for sharing!

    1. I had that idea at the beginning but was having a hard time finding some. I remember as a kid there were huge glass ‘stones’ in the faux fireplaces. I used to marvel at how they bounced the light. However they are not easy to come by… I keep my eye out for great terrarium/aquarium stones as well. It’s amazing what crafters amass…

  5. I love this so much! I made a big, purple geode! I would vote for you for President because YOU are a genius! Thank you for sharing this great idea instead of just keeping it to yourself.

  6. Do you have any pictures of the process. I’m a more visual person. Love the pics of finished product but all I see are ads and no pics of your steps in the article. Thanks.

        1. I’m not sure why that is? I have checked the site and it is fine. Maybe you need to wait til it loads? There are a lot of pictures so it may take a bit of time. Maybe try on a different device. Link here

  7. Wow Barb these are amazing. Because I was going through Pinterest to view this there were ads instead of your pictures. I went directly to your website and was able to view them there! Thanks. I am a rockaholic and so is my mother-in-law. Guess what she is getting for Christmas!! All your stuff is awesome. Thanks for sharing!

    1. I really don’t know how that idea popped into my head… I think I had some leftover concrete from a project and I try to experiment. Plopped it on some plastic and was amazed at the smoothness – ta-da! An idea is born!

  8. You are one creative gal!! loving this idea. I am moving soon and will have the opportunity to decorate our new home. Naturally, I have a beer budget but champagne tastes–which is why I love your DIY projects as they all look beautiful but don’t cost a fortune! Thank you so much for generously sharing your ideas!!

  9. Hi there
    I saw your link tothe geodes through a diply article. Just beautiful. The pics were onthe article but when I go to your website the are no pics. One simply wouldn’t load but i got it through the error code. But the were no other places evenfor the pics. For me this isa very difficult craft as I’m not very versed in working with these mediums so being able to see step by step photo is very important. I was wondering do i have to donate to for blog to see them as it seems the adds are in place of the photos.

  10. I love this. Do you have a video of this process. I’m very visual and it’s much easier for me to do after seeing it done.

  11. This is just so fantastic! Thanks for the step by step!
    Question: is there a reason you can’t set the crystals directly into the concrete? I know you still need to glue other layers in, but I was curious if there’s a good reason to wait and use glue?

    Thanks again!!

    1. Well, that could possibly work but it might be a problem when some are too thick compared to others and then you van’t fiddle with their placement. I’ve yet to combine glass directly with concrete but it’s on my to do list… Let me know if you try it! Geode on!

  12. I am thinking of doing an acrylic pour on mine do get the geode look. Yours are beautiful. Love the cracked glass idea.

  13. I am not crafty at all. I love these. They are so gorgeous. Is there anyway I could buy geode slices from you?

    1. I’m sorry but the last concrete thing someone insisted on buying ended up getting smashed in the mail, so it was a double loss for me. Maybe someone will make you one…

  14. Barb
    I like your big fantasy, make delicious things and your instructions are really well done and precious!
    Thanks
    Simona (Italy)

  15. I’m in absolute awe…. These are beyond wonderful! I need to get some of that cement ASAP! Is the final piece heavy? Have you tried using a cut wood base to make something sturdy like a table? I was thinking of mixing hypertufa and then adding crystals before it dried, but then I found this amazing, spectacular tutorial. I’ve been following crafts tutorials for a loooong time, and yours is hands down the best I’ve seen! I cannot wait to start playing with it! I will now be a grateful fan of your site!

    1. Oh Thanks so much! No the final piece is about the weight of rock. This concrete can be string at a thin thickness. I made the coasters with it as well. I have not done a table but have seen people pour resin on a wood shape to mimic the geode. I am always scouting out good glass for crystals! There is no shortage of ideas with my vivd imagination… only time to make them all!

  16. the first post I seen didn’t have pictures so I kept looking and found this post with the pictures. I am anxious to get started. Your work is so creative and so beautiful Thanks for sharing

  17. Oh wow Barb, your work is so inspiring. So glad it’s Friday, I have the whole weekend ahead of me too create. Thank you so much for your inspiration

  18. I am SO excited to find your site!!! Your talent is endless!! Thank you for sharing your amazing work. I have a brain injury, so I’m a little hesitant to try something like this, but you later out the steps so nicely. May I contact you if I get into this and am having problems? (I’m out of town for a bit, so it won’t be for a while).
    Thank you, again, for sharing your imagination with us!

    1. When ever I sense when someone is unsure I suggest to take the pressure off and do a small test. I do many little tests before my final projects. Also be aware of the correct concrete mix, as they are all NOT the same. There is a post here Also to keep things neat and easy for clean up see here

      Good luck, and yes I answer questions…

  19. Thank you so much for the amazing tutorial! I was blown away by the beauty of your creations. I’ve always been a huge geode fan, but they are so expensive and now thanks to you I can go “rock wild”! Several people in my family are getting these for Christmas, LoL.
    I think it’s very kind of you to post your wonderful tutorials….I checked out the lamp one also! Thank you, thank you!
    You are such a talented artist and an amazing lady!😀

  20. I just made the crystals from a bag of green glass beads I got at a yard sale for $1. Followed your procedure and it really worked!! What an awesome idea! Thanks for sharing!

    1. Yup, I felt a bit odd when I was ‘frying’ them. I do also hook up with a ‘glass guy’ who saves me his broken safety glass pieces as they are also very square-like. You just need to creative!

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