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Make your own Mold for Concrete

If you like gardening as much as I do, you may enjoy having some little concrete critters to add some extra interest. I’ll show you how to make your own mold to cast concrete forms. Perhaps you’d like some sweet little concrete birds perched on a rock. ‘And they last winter and summer, look great with aging and moss growth as well. Here’s a way to cast your own! This easy mold material works great and is quite inexpensive!.

Making-a-mold-for-Concrete---1a

You will need:

  • pure silicone caulking like this (make sure it isn’t latex)
  • 1 box of corn starch
  • rubber/latex gloves
  • a ‘non-precious’ bowl
  • vaseline (as a mold release)
  • a ‘critter’ to use as the master form (or make your own)

Making-a-mold-for-Concrete---1b

Since I have a weakness for birds, I was happy to find this fellow at a dollar store, not too large or too small. Also take a look at the shape, as it needs to be simple. In order for molds to release the form there have to be minimal ‘undercuts’. This means no areas that are very deep or complicated like holes or legs. A simple shape with surface details is best. This little guy has minimal details, short beak, and a rough texture which makes it forgiving in concrete.

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Yes, he’s shiny, as he(she?) needs a coating of vaseline as a mold release. Smear him up good!

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Now to make the molding compound. In a bowl that is not too precious (as this may not come off) put a pile of cornstarch at the bottom. It’s sort of like making pasta dough… Put the silicone in a caulking gun, cut the end AND poke a hole in the tube, then squirt it into the bowl (I used about half a tube).

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I put more cornstarch on top and started to stir with a paint stick ( disposable)

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Once it starts to come together and become more like a pliable dough, you can get your fingers in there, trying to keep them covered in cornstarch

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Work it til it feels like a modelling clay.

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Knead it to have even texture and start to apply onto shape. You will need to flatten it and force it to wrap around the shape. You should try to get an even layer around all of the form. I find that about >1/8″ & <1/4″ is best. If it is too thick it will not allow flexibility to take out the master form. I planned that the bottom would be the opening for pouring (usually the case) so I left it empty

Making-a-mold-for-Concrete---11-madebybarb

I brought the ‘dough’ around to completely envelope the shape. Make sure you press against the form to capture all the details. This mixture dries and stiffens quite quickly. Let set for a day once you have covered all.

Making-a-mold-for-Concrete---12-madebybarb

Once it’s set it’s obvious you won’t be able to pull the form out of this shape as it is. You will need to make seams that allow opening and closing, I cut up the middle and also up the bottom under tail. Sometimes you can see the evidence of where the original seams were in the original manufacture of it.

Making-a-mold-for-Concrete---10-madebybarb

This allows the form to be pulled out. The silicone/cornstarch mix becomes quite stiff but still has some flexibility of silicone. I find it holds shape more that just pure silicone.

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Here he comes out quite easily due to the vaseline.

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You have now created your mold! Congrats! You may have some favourite trinkets that you can now mold.

See Part 2 for Casting your Own Critter out of concrete.

Be proud, you made it yourself!

I have many other concrete projects that are quite easy…

 

 

barbmaker

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

This Post Has 55 Comments
  1. Haha – well now I’m going to need to buy a house with a back yard to accommodate all these garden creatures. Great project! I am envisaging some little frogs on the roof deck now though …

    1. Yes, do! More garden opportunity! Funny you should say frog… which I also made a mold. Problem was, each time I’d take him out of the mold, the foot would break off. ‘Need to perfect it!

  2. So creative! I have been working with different medium and love working with concrete premix
    This is so cool love to do more molds . Thank you for sharing ,Linda

    1. Glad you share the feeling! It gets addicting! And I’m happy to see how concrete is starting to be an acceptable indoor material as well. I’m hoping to try some 2 part molds for more complicated things. Endless options!

    2. You are welcome! I have more ideas for some molding but Canada is too cold now for more. Subscribe and you won’t miss when I do more cool projects…

  3. Very nice! I made a birdbath using Vinyl Patch & it’s wonderful. Now I’m ready to use silicone caulk to make a mold from the birdbath so I can make many more for friends. I can’t grow the Elephant Ears perfect or big enough. Have you ever done this?

    1. Thanks for sharing! I am not familiar with the elephant ear plants here in Canada. I use the rhubarb leaves. If I am short on them, I use the big leaves from the thistle plant, usually many at the sides of the road. I find that silicone caulk/cornstarch mix can vary, higher on the silicone side to be more rubbery and stiffer with more cornstarch. It all depends on the shape of your original piece.

      1. Hi barbmaker I’m real interested in all manner of garden projects could you be so kind to send to my email step by step instructions to make these moulds as well any other projects you would not mind sharing thank you so much

        1. I have so many garden projects (under HOME > CONCRETE) here I am in the process of making an ebook that will be available soon. In the mean time you will just need to use each of the posts as they have much info and instructions on each. Happy making!

  4. Hello! I just would like to give an enormous thumbs up for the good info you may have here on this post. I will be coming back to your weblog for additional soon.

    1. Oh, I do hope you return. I don’t post too many tutorials but I strive to make them thorough and give the encouragement to try it. Thanks kindly

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  8. My brother suggested I might like this blog. He was totally right.
    This post actually made my day. You cann’t imagine just how much time I had spent for this information! Thanks!

  9. This tutorial is awesome! You really inspired me into trying to make a school of fish floating over my hosta garden. I was wondering, how many critters can you make with the same mold? Is it really resistant? – thanks! Jen

    1. Hi Jennifer
      I have used the bird mold probably a dozen times and it doesn’t seem to change at all. The only problem I could forsee is that if one part of the mold is too thin and you stress it too much to rip. I have made a few more lately and a quite complex one that is not posted yet. I keep marvelling how wonderful this end material turns out. The only challenge is to figure out where the openings and seams will be. Areas that will need more bending to release the concrete can be thinned (shaved off with a knife) if the mold is too thick. I always figure if it doesn’t work, I can make another since it’s so inexpensive. Before you know it… you’ll be looking at things all over the place in a different ‘can-I-mold-it’ way! That’s creativity! You can check out the sculpting tutorial to see how to make your own master form… Good Luck!

  10. Could you please advice me on what kind of paint I can use on my cement products
    spesialy the foutains

    Friendly regards

    Johanna

    1. Johanna: I like to keep things simple so most of the time I keep my concrete natural. My love for concrete is the longevity it has so adding a lot of paint will change that. Paint and water tend to not like each other very well. A surface paint will not withstand the fact that there is water in the fountain. For that purpose I would look into the professional grade concrete pool paint. (but even those need regular maintenance) I would suggest a good quality sealer (if you really want to paint it), one that is safe for birds as well. As you can imagine, that may be difficult to find. There are countertop sealers that are meant to be food safe. Depending on your location, there are different manufacturers.

      Over my many years of painting around the house I have found that paints that are in contact with water tend to fail, even though there are warranties etc. For colour you could also look into an acid stain as it penetrates the surface since it is a chemical reaction. I know I am not being very specific, but each region varies and I am still on the hunt for a good sealer (as Canada has even less choices)

      When in doubt contact the manufacturer… Good luck

    1. Petra: The mold is fairly sturdy and the elastic bands around it hold the cut closed. I have also discovered in my other molds that pinning through the seams also helps keep them aligned. It has worked quite well. If it is a nice clean cut and well wrapped with elastics it will be fine. If there is any small amount of leaking, it can be cleaned off afterward. Also see: the bunnies and hands.

  11. Hi Barb!
    I make papermache sculptures that are pretty simple in terms of detail. Do you think paper mache would be strong enough to make a mold? Can the mold be reused for multiple “editions”?

    1. Well, There are a few things to consider here. Papermache is not waterproof so you would need some way of keeping it dry (plastic layer or a good waterproof coating) If it is very stiff and there are ‘undercuts’ it may be really hard to get the concrete out. Even when I made the concrete bowls I used plastic that had some flex to it. Having said that, the Rapidset Cementall sets so quickly that it may be done before the papermache would deteriorate. Maybe there is a way to do a small test on a scrap of papermache. That’s how I learn most, by trying… good luck and let me know how its goes.

  12. Wow! So glad I found your blog. You are so creative! Have you considered using talcum powder instead of cornstarch? I wonder if the cornstarch will decay or mold. Probably not LOL it’s hardly real food. I am really enjoying exploring your blog. Thank you for taking the time to post all this!!

    1. Talcum is quite bad to breath in. I have some molds that were in the shed over the winter and they are still perfect. I am amazed how they don’t change or yellow etc. There are other starches like arrow root and tapioca that would probably act the same.

  13. I tried your concrete mold idea on an 6 inch figurine. I ruined an entire package of 100 percent silicone caulking. The mixture, when mixed with the cornstarch, never formed into a ball and stuck to my rubber gloves during application. Without any measurements in your video, it’s very difficult to get the consistency to work. I love your video, but it didn’t work for me and was just a big mess.

    1. Gee, that’s odd as I don’t have a video of that. That’s a shame. As I had stated in the tutorial the silicone is squirted into the bowl of cornstarch and I toss it carefully keeping the cornstarch between my fingers and the silicone as yes(!) it’s very sticky. It’s like working with dough keeping the fingers dry. The recipe depends on humidity etc so keep tossing and incorporating until mix becomes a homogenous ball of dough. I’ve done it dozens of times and no problem, but then I don’t stick my hands into the silicone. When I am in doubt of a new media I often do a tiny test run. Good luck

      1. I read on another website that silicone will stick to latex gloves, I’m going to give this one more try using different blue nitrile medical gloves.

        1. I am pretty sure silicone will stick to anything! Make a nice bowl of cornstarch and then carefully keep turning it IN the starch (thats what dough makers do with flour) and it will get less and less sticky as it absorbs the silicone. Keep gloved hands well coated with the cornstarch as well. Perhaps you can search youtube as well.

    1. I don’t have a recipe as it would depend on humidity etc. Just keep mixing in the cornstarch until it makes the right workable consistency. I gauge it to the silicone and estimate how much I will need to cover. Having more is better than not enough.

      As I have explained, keeping the silicone in a mass in the bowl of cornstarch (like eggs in flour) will make for less sticking to fingers. When in doubt do a tiny test. Good luck

  14. How do you get the mixture to be so smoothe? I have tried this, found it through you, and every time there are imperfections in the cast because the silicone and cornstarch mix wasn’t smoothe on the thing i was casting.

    1. Do you mean the mix did not thoroughly mix or the mix did not get into the details? I know it sets pretty quickly and becomes stiff. Do push/force it onto the shape quite well and try for even thickness. It’s not a time to get interrupted… If the mold is too thick it can be cut quite easily to thin out I found too. I have not had a problem getting in the details as you see here I did have one person mention that they found that the clear silicone worked differently than the white, but I think it was a difference in setting time.

  15. For some reason I cannot get the pictures to load. This is something I really want to try this summer. I have it pinned but really need visual aids. Thanks in advance!

  16. I want to mold some large pieces of bark to later use as a texture for some outside garden pieces, in mixing a larger amount do you recommend mixing and applying the finished molding material in smaller amounts? Like a building up process? Will it bond with itself as I add or does it cure quickly? I am thinking about the time it will take to mix a batch and the time ir will take to apply and if it can be done this way.
    Thank you for the great blog!

    1. When I made the big Garden Face I had miscalculated and had to run out and get more after I used the first part. I found that the second addition did attach quite well (apply good pressure) There was a small section where it lifted so I used a bit of the pure silicone like a glue there. It worked nicely. The mix does cure quiet quickly once you have the amount of cornstarch incorporated when it’s no longer sticky. If it’s the first time, maybe get a ‘feel’ by doing a small test piece. I have had some people not realize the importance of mixing, keeping the cornstarch between your fingers and the silicone and getting enough mixed in. Happy casting!

  17. I tried your corn starch and silicone caulk molding putty and the overwhelming chemical smell was extremely irritating to my respiratory system…so much, in fact, that I seriously considered a trip to the ER! It was almost as if I was inhaling pure ammonia fumes….outside, too! What happened?!

    1. I’m not sure if they are all formulated the same but it is not odour-proof. You may be more sensitive than others. I do try to direct the fumes away with a fan or work outdoors. Which brand did you use? The amount used will also play into the amount of fumes. I have researched a bit and what you smell is the citric acid that is being released as it cures. Perhaps your sensitivity and the amount/location was just too much.

  18. I made a clay head that has some good detail for making a cement sculpture. The clay is just sculpting clay so it doesn’t harden (although it might if I left it out) I’m wondering how hard I need to push to put the silicone and starch on it? I’m concerned it might “smash” the detail of the eye brows, mouth, eye brows etc.

    1. Oh yes, the silicone needs to be forced into the details. That’s a tough one. I don’t even think the fluid pour one would like the moisture content in the clay. Is it air dry clay or the plastercine type? I have used the polymer clay to cast from but it can be baked. Tin foil can bulk up the inside to use less clay.

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