This is a simple lamp project consisting of a standard lightbulb socket cast into a concrete cube, with the optional addition of a 3D printed lampshade on top.
- Concrete powder: I used Shapecrete, which had clear instructions on the package for mixing and casting and turned out great. This material is really cool because it can have a claylike consistency then harden into concrete, but at the higher water ratio I used to get a pourable consistency, it acts a lot like regular concrete.
- Concrete mixing materials: Cover your workspace in something like a tarp or brown paper to take care of drips, and have a bowl, stirrer and measuring devices ready for mixing, as well as a water source handy.
- Mold making materials: I used foam board, a hot glue gun, a ruler, a triangle, a pen, double sided carpet tape, and a utility knife.
- Lightbulb socket with cord and switch: This is available in hardware stores - make sure you get the kind that has the cord on the switch, not the side of the socket, because the socket will be totally encased in concrete.
- 3D printer and FDM material
Step 1: Make a Mold
The lamp shown here is 3.5" x 3.5" x 2.5", so you'll need to build a rectangular mold with those inside dimensions. Sheets of foam are great for creating a casting mold, because they don't absorb water, demold easily and leave a smooth surface on the face of the concrete. They can be cut easily with a utility blade - use a triangle or measure carefully to make sure the pieces are square, and don't forget to account for material thickness in your dimensions. Stick the panels together with hot glue - it's okay if the joints aren't perfect, any extra concrete that gets in there can be broken off after demolding. I attempted to seal them with hot glue and it just created a melty mess, but if you want a super clean result you could try using silicone or some other sealant.
Step 2: Attach the Lightbulb Socket
Use a double sided tape, such as carpet tape, to attach the lightbulb socket to the bottom face of the mold (which will become the top face of the lamp). Remove the paper from one side of the tape and stick the socket down, then cut around it with a utility knife. Peel away the paper on the other side and stick the socket down in the middle of the mold. *Note - you can see here that I used pen to mark the exact center of the mold, but the marks translated exactly onto the concrete! So don't do this unless you want marks on your finished product.*
Step 3: Cut and Trim Lamp Cord (optional)
This step is useful for getting a clean detail where the cord leaves the concrete block and for adjusting the length of the lamp cord if necessary, but requires soldering and a bit of extra trouble so you can definitely skip it. If you'd prefer not to do this step, just cut a slot in the side of the mold to fit the cord into, then fill the gap with hot glue.
To cut and trim the lamp cord: remove the screws on the lamp switch and open it to show the cord inside. One side of the cord is continuous, and the other is broken with the two ends pierced by the switch - check this out so that you'll be able to put it back together later. Cut the continuous side so that the end of the socket cord is free, then drill a small hole in the side of the mold and pull the cord through. Trim the cord to length if you prefer, then cut and strip the ends so that the two longer ends can be soldered together. If you lose track of which strand is which, check for ridges - as long as you match the ridged strands together and the smooth sides together, it doesn't matter which side the switch is on. Solder the two longer ends together and wrap with electrical tape, then insert back into the bottom switch housing. Close the housing with the top half, making sure that the small metal teeth on the side penetrate the short strands of the cord, and secure it with the nut and screw you removed at the beginning.
Step 4: Pour Concrete
Follow the instructions on the side of the Shapecrete container to mix concrete of a pouring consistency. Note that the water should be added to the bowl first, then powder mixed in. Once the concrete is fully mixed, pour it slowly into the mold so that you don't disturb the socket. Leave the mold to cure on a level surface that won't be damaged by some water leaking out. Follow the curing time instructions on the package to know when it's safe to demold.
Step 5: Demold Lamp Base and Add Felt Pad
This step is simple - just rip the foam panels off of the concrete. They should come off easily and leave a smooth surface. If there are ragged edges on corners where the concrete seeped into the seams, you should be able to break them off with your fingers. To keep the lamp from scratching tables, trace the shape of the base onto a piece of sticky felt, then cut it out and stick it on the bottom of the lamp.
Step 6: 3D Print a Lampshade (optional)
This step is also optional - if you have a cool lightbulb and want an industrial look, leave the lamp as it is.
I used SolidWorks to create a lampshade that was slightly bigger than the base, with a shelf on the inside edge so that it sits nicely on the concrete base. The diagonal lines are for strength, since the walls need to be very thin (as thin as your printer can handle) to transmit light, but they also look cool when the lamp is lit.
Step 7: Assemble and Light!
Find a lightbulb you like, screw it in and stick the lampshade on top - done!