Make a Mold Support & Cast your Concrete

Apparently bunnies multiply like crazy! Well, I can surely agree. After making a Latex Mold of my sculpted bunny the next step has assured some great castings. It is quite simple to make a latex mold support

After the Latex mold:

The latex mold seemed to be so great that I used it right away and cast a bunny. It looked somewhat ok but I soon realized that he was much fatter and wider than the original. The problem is the concrete (or plaster) will push the soft flexible latex wherever it can and make a distorted version of the mold; almost like inflated.

To use a latex mold you should have some way of properly supporting it when pouring. I have used wet sand when the mold has been more flat but in this case I did not want the repeated fussing

The Plaster Mold Support:

I decided to make a simple & quick plaster mold support. Using some flannel fabric cut into squares that were wider than needed I dipped them in a slurry of regular plaster of Paris. The original sculpt/object must be in the latex mold while making the mold support.

This is much like the concrete draping since it impregnates a fabric wth something that will solidify it. I was not too fussy about perfection here.

The concept is that it just needs to prevent the soft latex mold from bulging from the inside weight of concrete (or whatever you pour in it) It also needs to be able to be dismantled to take the latex off the casting. In my case a centre opening would suffice.

The plaster sheets were fashioned over half of the form somewhat loosely. I did not want the plaster to get caught in any undercuts; just to hold the basic outside shape.

My ‘impatience’ decided to make both halves at once. To assure that the second half did not adhere t the first half and then no allow me to take them apart I used a plastic barrier.

If you’d rather watch:

The ‘cling film’ over the first half let me layer the second over the edge. The usual practice is to but the edges and have some sort of ‘registration’ of the parts. Registration means that the parts fit together a certain way like puzzle pieces. The over lap is my version of having a specific fit. Once dry/cured the pieces are quite hard and can put pulled apart but then reassembled to cast the form.

This is the finished 2 part mold support. (notice it sitting on the latex mold outside flange) The bunny there is the distorted wide one made without the mold support.

Take the support apart to be able to take out the master sculpture.

Pull the elastic Latex mold off the master sculpted piece.

Using the Mold Support

To be able to now use the latex mold inside the mold support it needs to be kept together. Some strong elastics do a great job.

Pouring Your Casting:

The mold needs to be supported in a vertical and level place while being filled. In my case a container held it quite well. You could use some rags in a bucket, whatever will not move.

The Concrete Casting:

The concrete that I prefer is a commercial mix; (so I do not have to mix myself) Rapidset Cementall. It is a very strong mix compared to regular concrete and also has the fine sand to pick up every detail. The bonus is that in 1 hour I can take it out of the mold.

Take apart the 2 halves of the support. Let me tell you; I like this assurance of form…

It is also so gratifying to pull the latex mold off the casting like a glove! See the difference on the 2 bunnies back there? Right one – no support, left cast with mold support.

From left to right; concrete casting, original sculpture, latex mold, Plaster mold Support. Works great!

Finishing the Concrete Bunnies:

One of the challenges of painting concrete is not losing the charm of the characteristics of the concrete. I HATE brightly painted concrete since it looks like awful plastic.

To keep the grey texture I sparingly use a wash of dark acrylic to seep into the crevices and give some definition of details & texture. Concrete’s porosity sucks the paint right away… so be sparing.

Bunnies have sweet colouring around the eyes I keep the dark away from it and accented wit some light acrylic. If you keep these outside they will eventually need redo or you will let them ‘weather’. If it is transparent paint then any failing parts will not be obvious.

Concrete likes to breathe. If it can’t it will ‘push’ the finish off as we see on those driveways that need resealing every year. The sidewalks seem to be fine without… So I do not use a sealer (call me a rebel)

If you want even a bit more accent to the texture of the fur a bit of dry-brush technique will make the texture stand out. It’s my secret technique for anything that is relief.

So Many Bunnies:

Since casting is so simple (I have been making them indoors) I kept making more… One bunny is never enough.

They are hiding under the allium that are sprouting (Canada is still cold) but look quite natural.

Happy Easter (or whatever holiday celebrate) with family and friends. Maybe you’ll join me in making bunnies & Smiles.

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11 Comments

  1. bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies, bunnies! Love bunnies – even have a soft spot for the big brother that looks like he needs to be introduced to Weight Watchers.. Thanks, Barb.

    1. Oh that’s funny! The BIG brother! I’m feeling like him lately! I remember seeing some statuary sometimes that looked a bit odd and now I know why. Mold making can take on much complication or not…

  2. Hi 🙂
    I just want to thank you so much for the effort and skill that you share with us. I’m a big fan of yours and I’m totally inspired to get molding. I’ve been putting off concrete things for along time because I’m a bit scared to fail but my concrete skulls are not going to make themselves 🙂 I love the Green Man too. He shall be an addition for sure.
    Long story short, I just wanted to say thanks xo

    1. That is so appreciated! It has been a labour of love (stress labour). If you are apprehensive it might be worth it to just do a couple small tests before diving in big time. Simple bowls are quite easy to cast in some plastic containers. Once you see how it cures, etc you’ll feel less nervous. Make sure to be aware of any safety concerns as well. Good luck!

  3. Barbara,

    Thank you so much for your informative article! I am trying to learn how to make large concrete pots for gardening, and I have been struggling immensely with the mold form on the outside. Can you tell me what you specifically used for your ingredients?

    1. As I have shown on the video and post I used a plaster form to help keep the latex mold in shape when filled. If you are making large pots then the form would have to be extra strong. The shape needs to be considered when making a backer mold. It may need a few pieces to be able to pull them off afterward. Fibreglass can also be used to make the backer molds and be bolted to hold together. As you see, it is quite a procedure. Concrete gets heavy quickly which is another challenge. I am mostly an artist and therefore prefer methods that afford me more creativity. I like the use of fabric (concrete draping) which also allows some easier making of containers. I hope that helps… this has some ideas about mixes as well…

  4. Hi Barb,
    Love your bunnies, beautiful detail! I want to paint a star gazing concrete hare I made from a mold. Do you suggest Liquitex paint if it is going to be kept outside? what do you think about Patio Paint for outside. Thanks for your reply.

    1. Thanks! I had made some painted rocks with my daughter using Patio Paint many years ago, (could be over 15 years) and I would still come across them in the garden and be surprised at how they held up. I’m in canada so that is quite something! My main observation is that if you paint concrete it’s best not to try to make a thick covering that covers the whole thing. Then it is more likely to peel as concrete tends to breathe and moisture may ‘push’ off the layer. If you paint only some areas, not to thick, then it tends to stay better. Plus, if it fails it is not as unsightly/noticeable. I have an old metal bucket and rusty shovel that I painted over 15 years ago with that paint and looks great. These items are in areas where they sit in water either. Good luck!

  5. Thanks Barb for your quick reply. I will use the Patio Paint but thin with water and do one light layer. Good luck with your felting projects. I love that you are curious and not afraid to try something new. Good luck with your next projects.