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!.
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)
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.
Yes, he’s shiny, as he(she?) needs a coating of vaseline as a mold release. Smear him up good!
Making the Molding Compound:
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).
I put more cornstarch on top and started to stir with a paint stick ( disposable)
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
Work it til it feels like a modelling clay.
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
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.
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.
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.
Here he comes out quite easily due to the vaseline.
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…
If you have a complex original sculpture you may also consider making a latex mold as it will be very very stretchy compared to this silicone mold.