Casting an Aluminum Anthill

Casting molten aluminum into anthills is definitely not an original idea, but I still wanted to try it. When you normally cast aluminum into sand with a foam mold, the most exciting moment is when you first pull it out and see if it worked or not. When doing this with anthills, it is even more exciting. If you use a foam mold, you know generally what the finished piece will look like, but with ants, you have absolutely no idea of what will come out of the ground. When I came across a large opening for an anthill in our driveway, I had to give it a go.

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Link to video: https://www.youtube.com/watch?v=PHZgTz-Egfg

Before you can even begin, you have to locate a large anthill. I have tried to cast the little tiny hills that pop up on sidewalks and roads, but have never had success in casting them. My guess is that the tiny hole fills up with sand before the aluminum can enter, or the surface tension of the metal is too high to allow it to flow. Don't get discouraged if you can find one right away. I just kept my eye out for a while, and eventually found one that was perfect.

After you have located the colony, it is a good idea to build up the sides a little bit. When you fill up the anthill, you need to have head pressure or the metal won't flow down as far as it should go. To achieve this pressure, a reservoir of aluminum needs to sit above and keep force on the molten metal. If the sides aren't built up to make a dam, it just spills out and you get a 1,221°F mess to clean up. To avoid this, I used sand taken from the Mississippi river and formed a bowl shape with the entrance hole in the center. Make sure to not spill any sand down into the hole.

That dam serves another purpose once the aluminum is cooled off. You can flip the entire structure over and you have a solid base to hold it on.

When your anthill is prepped, you can start on the forge. My "forge" isn't really a forge at all. It consists of a couple fire bricks arranged in a semi-circle with a furnace blower aimed at the opening. I have used normal bricks in the past, and they do work but all end up cracking from the heat.

The forge runs on scrap wood. It would be much better if I used charcoal or coal, but scrap wood is free, and works well enough with enough air supply.

For the aluminum supply, I find reusing old soda cans works very good. You can use scrap aluminum, but it is more difficult to melt, and the pop cans melt within seconds. You will need a decent amount, and they can be easily found at recycling centers or even picked up on the side of the road.

Importantly, don't forget the necessary safety equipment (fire extinguisher, welding gloves and apron, face shield, tongs, etc.)

Make sure to have everything you need to completely finish the process, because once you light the forge, things move along really fast, and you often don't have time to run inside and grab more supplies

After you light the forge, you can start to blow more air into the fire. The rate of which the air is supplied really determines how hot the fire is. You have to be careful though, you cannot move the fan too close or you could risk blowing coals out of the forge.

After the first couple of cans are melted, things move along faster. The aluminum that is already molten surrounds the new cans and heats them up much quicker. Keep melting more until you are sure you have twice as much as you need. When I pour the aluminum, I find that I always could have a little more, so it is better to be on the safe side. You don't really know how big the anthill is, so it is better to have too much instead of too little.

Be gentle when pouring. It is easy to knock a rock or a bunch of sand into the hole, clogging it up.

After you let the casting cool for a long while, the fun part can begin. I actually let mine sit for only an hour or so, and while digging it up, still felt the intense heat. The dirt surrounding the casting insulates the aluminum, causing it to stay hotter for a longer period of time. Be cautious when pulling it out of the ground, you can break off little chunks (I accidentally did).

After the casting is out, pour water on it to cool it down and clean out the dirt and rocks.

After the piece is removed from the ground, you could stop right there. I wanted a nicer base to sit on, so I decided to build a custom one. The casting came out with a longer oval shape, so I drew a suitable shape onto a piece of 1/2 inch red oak. You can easily draw ovals similar to mine by securing two nails a distance from each other, and using a loose loop of string strung in between them. Once the shape was drawn, I used my cheap not-very-good bandsaw to it out.

I knocked off the edges with a chamfering bit in the router. Also, I drilled a small hole and pounded in a little aluminum rod to help support the weight of the casting.

I finished the base with two coats of water-based varnish. After the first coat dries, I sanded it with fine steel wool and brushed on the second coat.

I attached the casting to the base with glue. The bottom of the base wasn't flat, so I needed a glue that would foam to fill the gaps. I really hate using it, but I resorted to Gorilla glue. When it foams, it fill gaps nicely, but also swells and covers everything that you didn't want covered. To prevent this, I applied only a small amount to the center of the base. For the support rod, I used 5 minute epoxy, which is definitely a more reliable friend.

After the glue was set, the project was completed. It was definitely a fun one, and I might revisit it again in the future. If you are interested in buying this piece I have made it available on Etsy here.

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