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Picture of Cast Concrete Pendant Necklace
This is a little cast concrete pendant I made for my lovely girlfriends' birthday a little while back, paired it with hammered copper bracelet and a fancy little display stand.  

This whole project takes roughly 2 or so hours from start to finish, and the results are great, she has gotten a ton of compliments on the piece, and it only cost me about $3 worth of materials.
 
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Step 1: Tools and Materials

To make this concrete pendant, there are a few materials and tools that you will need to gather before you can begin.  

Materials
  • Plywood or solid wood-  2 pieces cut to the same size, these are going to end up being the form we cast the concrete in, mine were approx 4 1/2" x 6"
  • small piece of solid strand copper wire, I used the ground wire out of a small piece of 12-2 romex about 2" long
  • Kreg pocket screws or really any 1 1/4 screw ( I like the Kreg ones because they are self drilling and washer head)
  • Hydraulic cement
  • Mixing cups and a stirring implement-  I used a couple of small solo cups and a plastic spoon
  • Finish- concrete sealer or a lacquer
Tools
  • Router Table
  • Router
  • Core Box Bit- I used a 5/16
  • Dowel- same size at the core box bit, mine was a 5/16 again
  • Drill/Driver
  • Clamp
  • File
  • 220 and 400 grit sandpaper

Step 2: The Setup

Alight, now that you have all the tools and materials pulled together, its time to get to the fun stuff.  

First things first we need to set up the router table.  

Put the core box bit in the router and set it so that it comes up through the top of the table exactly half of the diameter of the router bit.  This is pretty important as you are joining the two boards together to create a cylindrical form to cast the concrete in.

Take a measurement of the width of the boards you have set aside for making your forms.  Mine are approx 4 1/2"w x 6"l.  Offset your router fence so that the bits hits in the center of the board, you don't have to, but it makes it easier to align the two parts of the form later.

Now clamp a stop block to your router fence,have the distance from the edge of the board to the center of the bit be slightly longer than what you want the finished length of your pendant (mine was roughly 2" )

Rout the grooves in each of your boards.  Feed the board all the way to the stop block then power down the router and wait for the bit to stop spinning and remove the board, repeat with the other side.

Step 3: Prepping the mold

Now that we have everything routed out we need to mate the forms.  Align the 2 halves of the form, and insert the dowel fully, then clamp the pieces in place.  

As long as your dowel is the same diameter as the hole you routed, you should have really good alignment on the form.  Once it is clamped, you need to screw it into place and remove the dowel.

Take your ground wire out of the romex, and cut about an inch and a half to 2 inches of it and fold it in half.    

Now get the hydraulic cement and your mixing cups out and measure out the cement based on the manufacturers suggestions.  The Quikrete I used needed to be mixed 4 1/2 parts concrete to 1 part water.

I measured 9 teaspoons of the cement into 1 cup and set aside 2 teaspoons of water.




Step 4: Making some concrete

Alrighty, we are ready to start casting.

get your dowel, hammer, concrete, water, and copper out and set them aside

Mix up your concrete and water, you need to work quickly as the hydraulic cement sets up incredibly quickly

Force the concrete into the mold, and pack it in with the dowel, gently tapping it in with the hammer.  Pull out the dowel and repeat the process until you have nearly filled the mold.

Quickly take your formed wire and force into the concrete, as close to center as possible.  

On this one i was slightly off, the concrete started to dry and as i was taking the pictures...

Now you just need to let this one sit for about 20-30 minutes, don't wait too much longer or else its tough to get out of the mold.


Step 5: Removing the pendant from the mold

So its been about 20-30 minutes since you cast the concrete and  clicked next on the bottom of the last page, so lets get to demolding that pendant!

Unscrew the two halves of the form, and use a screwdriver to pry them apart.  

The pendant sometimes sticks pretty well to one side, if you gently but firmly push from side to side on the pendant, it will pop out after a minute or two.  

Take a file or some sandpaper and square up the top of the piece, then sand the entire pendant with 220 grit sandpaper until its nice and smooth.

now that it is cleaned up all nice, hang the pendant from a string and start topcoating it with some lacquer or some concrete sealer.  I used lacquer on this, just because i always have a couple of cans hanging around.  

Build up a good amount of coats on the piece, letting them dry for a few minutes between each, and after about the 3rd or 4th coat, start sanding in between coats with some 400 grit sandpaper.  Repeat until you are left with a finish that you are happy with.  I did probably close to a dozen or so over the coarse of 2 hours, and got a great polished glossy look.

Step 6: Finished product

Picture of finished product
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And thats it, string a chain, or piece of string through the copper ring and you have a necklace.  

I ended up putting this on a rose gold chain for my girlfriend to more closely match the copper ring, and she was very happy with things.  I gave it to her at the same time as the Hammered Copper Bangle  I posted on here a little while back and made a little wooden display stand for the pieces.

Hope you enjoyed the instructable, Thanks for reading and let me know what you think!  
HBrown054 months ago
am I the only one who is thinking this looks like a tampon... I like the idea but.
Duplicity1 year ago
I have not made a necklace, but have made concrete weights before. An easier trick I have used has been pieces of copper water pipe or pieces of plastic PVC pipe. If you seal one end and lightly spray with silicone spray to act as a mold release you can just pour the concrete in, add you wire loop and when it hardens just tap it out from the bottom. You would then clean up if you were going to lacquer but the silicon spray actually leaves a really cool and durable finish. With something like pipe, it is super smooth when you pop it out. No sanding required.
jbeaton (author)  Duplicity1 year ago
thanks for the idea, sounds like that would work out pretty nicely. For this one i wanted the rounded bottom just for aesthetics, but to get a cleaner cylindrical look that would definitely work. I think I may give that a try the next time I am doing some casting. Thanks for taking the time to read through and post!

Using Duplicity's method, you can always shape the end of the cylinder after demolding to get the rounded end that you want.

Is it really completely cured enough to seal it that soon? Seems like you'd want this to set for a day at least before sealing it.

artworker1 year ago
How much does it weigh? Just asking as I am planning to make something complex and little larger than this.
jbeaton (author)  artworker1 year ago
just threw it on the scale and it weighs 22g or about .8oz. not very heavy at all
Cool! thx!