Disclaimer: I am not a professional skull maker. I dabble in a lot of things and sometimes I luck out. In fact I am reminded daily how lucky I am by my wife. This is likely not the ideal mould making tutorial, just something I pulled together at the end of the concrete contest because I am a perpetual procrastinator.
So vote for me or your skull may be the next on the pyre.
Just kidding, I read the contest rules and your votes are meaningless…
ON TO THE INSTRUCTABLE!
“So you’re making a concrete skull? And you already had a skull to mould from, and you know how to do this? Wait… other people want to know how to do this? Who are you?”
This from the beloved peanut gallery holding my camera. Anyhow, I thought it would be amusing to have a set of concrete/refractory cement skulls for my fire pit. You know, for when the inlaws come over, or when we are meeting new friends, pagan harvest festivals, whatever. I felt the house needed a little more... how do you say... Genghis Khan. Concrete skulls as bookends in my kids room? sure why not. Garden edging made of skulls, my neighbors will love it. What’s not to like.
I have a lot of extra stuff laying around. Concrete coloring, concrete additives, fiber reinforcing from previous projects, lots of stuff. So I used it. For my concrete skulls. Making a silicone or fiberglass mould would probably be more of an exact replica but I didn’t have any at hand last minute when i decided to start this and don’t know how to use it well. I’ve made a LOT of weird things from concrete.
You will need:
Skull – find one that is hollow inside and fairly thin walled
Mortar mix (or Portland and sand) - Refractory cement – if you want to make them for a fire pit, otherwise mortar mix is fine
Mixing container and trowel
Mould release – spray on wax, veggy oil, actual mould release…
Something to vibrate the concrete with – no not that. An orbital sander works though
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Step 1: Alas Poor Yorick!
Find a suitable skull. The way I make the mould gives a close copy of the skull I used but with less detail which i find acceptable. Not all skulls are made this way, this one is rotomoulded I think so the inside is pretty close to the outside. If you get a foam skull then you will have to make a fiberglass or silicone mould first
Step 2: The Mould Begins
Take a look at the skull.
A really good look. There will likely be mould lines that someone else thought out already. You’re going to use them. But ensure they will work for an unmoving unrelentingly exact mould material like concrete. If there are any undercuts that you cant get away from now is the time to fill them. I like epoxy putty. This particular one only needs its jaw removed, that’s why I chose it.
Step 3: Cut Cut Cut - NO NOT THAT!
Use a box cutter to cut along the existing mould lines. Carefully. Mostly because trips to the ER are expensive, but you don’t want to mess up the mould either. Separate it into pieces. In my case its 3. Cut a hole in the bottom, approx. 1.5’’ round where its not obvious, this is where you fill from. Any smaller and you’ll be spooning the mortar mix in… not fun.
Step 4: Humpty Dumpty Dance Is Your Chance
Reassemble skull. I used gorilla tape to "stitch it", its probably not the best but I had it handy. Run a line of elec tape or other semi waterproof sealant. Honestly I could have used gorilla tape all around but I was afraid I couldn’t get it undone, its seriously sticky stuff.
Step 5: Vibration Is the Key
Set skull up to pour. Make sure its steady. Ideally put it in something you can support well. You’re going to be vibrating it and you don’t want it to come apart. I braced it in a small box and clamped the whole shebang.
You should spray the inside with a mould release, or prepare to cuss a lot later. I’ve heard PAM cooking spray works.
Combine mortar mix and water until its like a thick peanut butter. Add any coloring you want and remix (I used a little bit of black but didn’t mix it well and its not uniform, next time I’ll probably use more) If you are lucky enough to have a gallon of concrete superplastizer laying around like I did (told my wife it would come in handy!) use a teaspoon full. It makes the mortar flow so much better and end up looking nicer. Pour in half of the mortar and vibrate. Pour in the rest and vibrate a little more. Almost there…
Wait a day or two.
Step 6: No Clever Title, Its 11pm
Remove skull from concrete. Hopefully it removes, otherwise you either 1.) didn’t apply enough mould release 2.) didn’t ensure it was free of undercuts/form issues. Try to pry it out without damaging the concrete.
Compressed air between the skull and mould may help pop it out. Water may help. Freezing may help. Cursing definitely helps. Once you pop it free if its full of air bubbles or large voids you didn’t do it right in the vibrating phase. Try again. Small bubbles can be filled with cement slurry, large voids are harder. I’m not too picky. I mean if it looks a little battle damaged, it is in a fire pit. Pretend it’s your second worst enemy. ** Sips beer from skull of worst enemy **
Step 7: Lather, Pour, Repeat
Repeat until your neighbors hate you or you have a BBQ pit that makes Rob Zombie jealous
Runner Up in the
Stone Concrete and Cement Contest