Concrete / Refractory Cement Skulls

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Introduction: Concrete / Refractory Cement Skulls

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.

Supplies:

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

Water

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

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

Step 8:

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    31 Discussions

    0
    dvrnhll
    dvrnhll

    8 months ago

    These sit right in the firepit and have held up great since I made them
    for a Halloween party last year. I just poured the cement into the hole
    at the bottom and cut off the plastic skulls after letting them dry
    forever! Great project idea. Thanks for sharing.

    3
    allenswan
    allenswan

    1 year ago

    The skulls look great. Have you fired them up in the pit? Do they last? Please post after testing them.

    0
    eciton
    eciton

    Reply 1 year ago

    i have not yet. waiting on refractory cement to come in. the ones made from pure will not likely last long in a fire even after fully curing. but man refractory cement is expensive, i may try to cut it with mortar and see how it does.

    0
    allenswan
    allenswan

    Reply 8 months ago

    I have not used any refractory cement before. So I really don't have any suggestions.

    1
    berryjp
    berryjp

    Reply 1 year ago

    Skulls resting in flames is an arresting image, however I would strongly suggest researching refractory cement process and curing time before subjecting them to high heat. Heat + water = steam, a volume expansion of 1 to 1700 ! Not the best combination when encapsulated in a rigid material.
    Do not use standard concrete in a fire as it is porous and retains water.
    Moss covered skulls casually laying about the garden, much safer. Liked your casting process.

    0
    eciton
    eciton

    Reply 1 year ago

    As long as you follow castable refractory cement curing guidelines from the manufacturer you should be fine. You can't just cast them and chuck them in the fire. It would be like firing a newly made pizza oven full blast, expect failure.

    I think these mortar ones would likely be ok surrounding a fire pit, I definitely wouldn't just toss them into a raging fire. To be safe if it's near a significant heat source refractory is a better choice all around.

    0
    jsnow12
    jsnow12

    Reply 8 months ago

    Would you happen to know of a good refractory cement to use for these?

    1
    eciton
    eciton

    10 months ago

    just an update. even out of cheapo mortar they look good around a fire pit, they're protected from the majority of the heat. after a 4 hr fire they didn't even sizzle when we put it out.

    skull.jpg
    0
    Shep4u
    Shep4u

    Tip 11 months ago on Step 7

    Try washing up liquid as a plasticiser, also antifreeze in the water will help if you're leaving it to set outside in winter.

    0
    Dr Will 304
    Dr Will 304

    1 year ago

    I'm a physician who now works as an anatomist. I especially like the anatomy of the head including the skull of course.

    This would be cool to do with animal skulls too. Maybe a steer with horns.

    0
    oriojhell66
    oriojhell66

    Reply 1 year ago

    Yes, animal skulls!

    0
    ERALPD
    ERALPD

    1 year ago

    Great instructable :)
    this give me an idea too, that make this skull from coal:)
    Thanks...

    1
    eciton
    eciton

    Reply 1 year ago

    That's funny you say that, my initial idea was to make skull shaped fire logs using compressed sawdust and binder but it requires a much more durable mould and i just haven't had the time.

    1
    TeresaM7
    TeresaM7

    1 year ago

    Oh, I love these! Going to find some skulls for molds ASAP. :D

    0
    Dr Will 304
    Dr Will 304

    Reply 1 year ago

    I hope you mean the plastic kind.

    1
    TeresaM7
    TeresaM7

    Reply 1 year ago

    Of course. Hollowing out the real thing is WAAAAAY too much effort and ruins their value ;-)

    2
    eciton
    eciton

    Reply 1 year ago

    home depot has a bag of 3 for $9.99 that looked like good candidates for a nice 2 piece mould. i almost bought them but felt my wife rolling her eyes from 20 miles away

    0
    CraftAndu
    CraftAndu

    1 year ago

    Cool! Is there such thing as professional skull maker, though? :D

    0
    karlbamforth
    karlbamforth

    1 year ago

    Excellent idea and excellent project.

    How did they hold up in the fire pit?