Helping Hands

For those that can use an extra hand around the house!

I like to ask my students to think of some small thing in their life that could use a little extra assistance around the house. It can be small, from a toothpaste holder to a coat rack or an extra fist bump them when they finish their work. Then we make that idea more concrete!

• What: Helping (Concrete) Hands
• Why: Fist bumps forever
• Concepts: Casting and Molding, Woodwork, Chemistry
• Price Per Hand: ~ $2.50
• Materials:
  • For casting:
    • Concrete (quick drying Rockite works great)
    • Alginate for the mold (I used this brand)
    • 2-liter bottle (or other large container for casting)
    • Mixing stick
    • A small piece of cardboard
  • For mounting:
    • Bolt
    • Threaded insert (that fits bolt)
    • Washer (that fits bolt)
    • Nut (that fits bolt, just for setting)
    • Wood
    • Screws
• Tools:
  • Drill
  • Scissors (optional)
  • Utility knife (optional)
  • Saw
  • Sandpaper of Sander

Ready, Get Set, Concrete!

Whether you just chugged 2 liters of Hawaiian Punch or scrounged from the company picnic, you've got to prep that bottle. Cut off the top with a utility knife or scissors, and then dry out the inside.

Put your hand in in the position you want your cast to make sure there's enough room so it doesn't hit any of the sides. If it does hit a side, you're going to need a bigger container. Time to chug 3 more liters of Hawaiian Punch! Or just use a box. :)

If your mouth has been filled up at the orthodontist, or if you've ever dreamed of a purple heaven, then you know alginate well. Alginate is just amazing stuff to cast from living things. It's also neat that it's actually from the cell walls of algae.

Scoop some into your bottle that you think can surround your hand (a little less than half by volume), add water and mix. I used a brand called "Dermagel" from Douglas and Sturgess, and they recommend adding 1 part alginate for 1.5 parts water by volume, but I find that I can get good results by just eye-balling it aiming for a semi-goopy milkshake mix.

Get your hand in there! Once you've started mixing, your alginate is setting. For me, my hand got tired after a bit, so I used the side of the bottle to prop it up. To see if the alginate is set, wait 5-10 minutes and poke it to see if it feels like spongy but solid. If it is, you can start wriggling your fingers free and take it out. You can make it go faster by using warm water and keeping a higher powder to water ratio.

Wriggle that hand out of there. If your alginate moves a bit when you take it out, that's okay! It's part of the magic. It'll return (ish) to its mold state.

It's bolt time! We're going to set a bolt into the back of the cast hand, but you're going to need a little support to do so. Make a hole in a piece of cardboard with some scissors (2). Then slide a wide washer on your bolt and poke it through the cardboard. Hold it in place with a nut (3), and make sure that the bolt will hand low enough into your mold to be deep in the concrete (4). Remember, the head of the bolt will be inside the concrete. You got it!

Scoop up some concrete powder (I like Rockite because it's quick), and add water. Again you're going for a milkshake-like consistency. Pour it into your mold, making sure to move your mold around, angling it to make sure any air can escape from overhangs (like where my pointer finger curled in this mold).

Pour it to the top, and then place the bolt in the top. If you find the bolt is too far out, cut down the sides of your bottle until it's just right.

This is truly the most fun part of any casting process. Is it a hand? Did it work? Will the fingers break off? Is there a live animal in there? It's just so much fun to go on the archeological dig of the most recent fossil on the planet.

After your concrete has set, remove the bolt and uncover your piece. (Look! The bolt is in there!) You can slide alginate out of most things, and then begin to peel it away with hands and scissors if you like.

And inside is.......YOUR HAND! AS A ROCK! IT'S A MIRACLE! (I really do feel this way)

After you have a "HOLY MOLY, THAT'S MY HAND" moment or hour or so, you can start to clean up your cast. There will probably be little flakes of alginate, a few drips of concrete you don't like, and maybe some rough edges around the base.

I started with a a little water and a brush to take off some of the concrete dust and alginate, and finished up with sanding the corners around the wrist to make them nice and smooth.

If there are holes from air bubbles, you can always mix a little more cement and dab them in there. Concrete hand surgery is pretty forgiving that way. :)

Your mount can be any shape you'd like, but I chose a circle. I used a roll of tape to trace around, and then cut it out on a bandsaw. I sanded down the edges, and then found the center of the circle for drilling.

My favorite method for finding the center of a circle is this one!

This is a great little piece of hardware called a "threaded insert." It's adorable. It looks like a stumpy brass worm. It also is going into our mount.

Check the size of your threaded insert, and drill a hole slightly smaller than it in the center of your wood (1). Screw the insert onto another bolt of the same size (2), add some glue (3), and then use a drill to drive it down into the wood (4).

Now you have a great threaded piece of metal that you can easily screw your hand on to (5)! And you can trade out hands whenever you want.

If you want a more permanent hold, you can always do a more standard nut and washer method to hold the bolt in. If you do, just make sure to countersink them so they're flush with the wood.

When you screw the hand all the way in, you may have some bolt sticking out the back. Saw it down so that you can mount it flat on the wall.

To remove the extra bolt, screw your hand all the way in and mark which thread you'd like to cut it off at. Put it in a vice, and hacksaw the bolt off, making sure to support the hand when it breaks free. Then you can either sand, grind, or file it down to flush, and soon you'll have a helping hand you can mount on the wall! Huzzah!

If you want to put your helping hand up, it's easy to do! Screw the hand all the way in, and mark where "up" should be on the wood. Take the hand off, and then pre-drill two holes and insert screws. Drill them into the wall, making sure your "up" mark is facing upward. Then screw back on the hand!

You did it! Your helpful concrete hand can be used for all sorts of purposes. Whether it's used as a coat rack or a high-five or a toilet paper holder or a guiding pointer, it's there!

I am excited to see what you all come up with, so do share below if you make one! Have fun and keep exploring.