We needed a desk lamp and a DVD player stand; I had some remaining LEDs and wanted to make something stylish with concrete...

So I built this concrete desk lamp featuring:
- Retractable keyboard illumination
- Phone charger
- Pen holder
- DVD drive stand
- Clutter fence (more on this in the last step)

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Step 1: Designing It

A good project starts with a good design, and there are always enough unexpected issues requiring improvisation. I had relatively precise size constraints, and wanted to obtain a modern, minimalist appearance.

Functional considerations:
- Determine the overall desired final size.
- List the functionalities you want to bring in.
- Measure the DVD player dimensions.
- Think about all cable passages, and cavities (e.g. for the power supply).

Material constraints:
- Concrete walls should be at least 1 inch thick.
- Sharp edges are critical with concrete.
- Hinge anchoring is non-trivial, if near to surface.
- Concrete is damn heavy, so plan as many hollowings as possible.

Step 2: Building the Mold

1. Use a large enough plank for the base, and build the walls. Tighten with hot melt glue and nails.

2. Cut a vinyl sheet to cover the 3 largest sides. This is a leftover from vinyl flooring, and will bring a very even surface.

3. Fit the PVC sheet into the mold.

Step 3: Shaping the Bar

1. Cut out the aluminum bar to shape. Use a Dremel, files, metal saw, etc.

2-3. Fold the angle using a rubber hammer.

4. Repeat on the other end. Make the ends round, and drill the hinge holes.

5. Brush the surface with steel wool. This will bring a very even finish.

Step 4: Adding Inserts and Cavities

For the DVD player stand:

1. Cut a Styrofoam piece,
2. place it where needed, using much double-sided adhesive tape.

Sharp concrete edges are quite fragile, so we want slightly rounded edges (2-3mm radius is enough):

3. Using silicon sealant, create rounded edges.

4-5. Now, create all recessed areas and cavities, by adding their corresponding negative shapes, made of e.g. wood (or 3D printed):

- the plate (creating the top recessed area) shall have a well protected surface, the best would be use waterproof glossy paint; it shall be firmly glued/screwed to the mold;
- pieces to create cavities for the cable passages shall be firmly tightened, e.g. using small screws;
- brass tubes inserts for wire passages shall be well anchored, using hot glue;

The aluminum bar shall be screwed to its anchorage, covered with masking tape, and placed in order to create its future rest space into the concrete.

6. Oil all surfaces (except the brass inserts) to help later demolding.

7. Make sure the base is level.

Step 5: Preparing the Other Cavities

1. Cut Styrofoam shapes that will make the central cavities.

2. Tighten them on a wood bar, to be screwed to the mold. Remove and keep for later.

Step 6: Adding Concrete #1

1. Mix some concrete for a 3 cm-thick first layer.

2. Pour into mold.

3. Spread.

4. Add the prepared cavity shapes.

Then, proceed quickly to the next step, which must be completed while the concrete is still soft.

Step 7: Adding Iron Reinforcements

Add a liberal amount of iron reinforcement. I mean, literally stuff your concrete, with things like:
- Threaded rods,
- iron mesh.

Check that no iron touches the mold, else it will impact the final surface aspect.

Step 8: Adding Concrete #2, and Waiting...

Add more concrete to reach the desired overall thickness. Spread evenly with a spatula.

The concrete may be quite moist, so that the gravity can help getting an even surface.

Leave to dry for at least 10 days. Be patient, don't ruin your work!

Step 9: Demolding

Now is the time to demold!

1-3. Remove the Styrofoam.

4-6. Disassemble the outer planks.

7-8. Free the top recessed area and the cable passages.

Step 10: Finishing and Painting

1. Apply concrete sealer. This is an important step, as it will significantly harden the surface by gluing the grains together.

2. Optionally, fix the irregularities with primer and putty.

3. Sand. Re-apply sealer.

4. Spray paint, by multiple thin layers.

Step 11: Adding the LEDs to the Bar

1. Solder wires to male connectors.

2. Cut the LED strip to desired length (according to instructions specific to strip), and have a female connector at each end.

3. Test with appropriate voltage.

4. Stick strip to aluminum bar.

Step 12: Adding Power Supply, Switch, and USB Cable

I looked for power supply unit (PSU) delivering both 12V and 5V. The 12V will be used for the LEDs, and the 5V will be used as USB charger.

1. I found this PSU, delivering the two desired voltages.

Install the PSU:

2. Cut and strip the cable, and locate the GND, 12V, and 6V wires.
3. Connect the GND and the 12V to the wires going to the hinges.
4. Place the PSU into the central hole. In my case, the friction alone keeps it firmly in place.

Install the switch:

5. The 12V goes through the momentary switch. Circuit open when released, closed when pressed.

Cross the concrete:

6. Then, the 12V and GND go through the concrete, via the tube inserts, to their respective future hinge.

Install the USB powering cable:

7. Connect the GND and 5V to the USB cable, using a small piece of solder board. Check the polarity!

Step 13: Building the Hinge

1. The hinge is a critical part. It shall conduct in any hinge position, without making any contact with the aluminum bar.

2. A sheet of copper has been scavenged from a dead harddisk enclosure.

3. Glue the copper sheet on a 5mm-thick wood plate. The thickness must be sufficient so as to avoid any contact between the aluminum bar and the opposite contact. Cut the piece to shape. Make sure to have a good margin between the copper and all borders (including the hole).

4-5. Stick the plate onto the bar. Keep the holes well aligned and make sure that the screw will not contact the copper.

6-7. Take the previously prepared connectors and cut their wires to length: The connector side goes to the LEDs, and the wire end gets soldered to the copper.

8-9. Build the opposite contact plates, to be glued on the concrete side. Once again, avoid contact with the screw. Those contacts should not touch the aluminum bar either. Solder the contacts with the wires coming through the concrete.

With an ohmmeter, check for proper contact between the copper plates, and check that no contact is ever established (for any hinge position) between the copper and the aluminum.

Step 14: Final Step

We are now close to the final product!

We want to create a layer of silicon on the bottom side, in order to protect the tables from being damaged by the concrete, and also to avoid slipping.

2. Tape the bottom side so as to reveal the surface to be covered.
3. Add some silicon joint sealant,
4. spread it evenly,
5. and remove the tape.
6. Let it dry for half a week.

The final touch is the top mat, to protect objects against any shock on the concrete, and add a touch of friendly elegance.

7. Cut some fabric to the size of the top recessed area.

Step 15: Conclusion, Thoughts and Learnings

A few thoughts and learnings

- Adding some recessed ornaments (during the molding process) to the front side would be nice, and make it look less massive.

- Making a mold with even higher quality of surface could allow to not use any filler/putty, and leave the concrete surface in a more natural state.

- More functionalities, like card reader, USB hub, mini planter, mini speakers, etc. could be added. The technique of creating precise cavities shall be well mastered.

- The hinge anchorage was quite difficult to make. In fact, the concrete was too bristle, and I had to repair the place by creating a sand+epoxy paste.

- Concrete with epoxy/resin or fiberglass reinforcement, or foam concrete, are things I'd like to try.

Why taking up so much space on a desk?

Well, the actual intended use is for our computer-in-a-shelf, so that objects do not roll behind the drawer, and so that we can type at night. So, it is precisely intended to occupy space, to leave no room for the mess.

Conclusion

Concrete is a great material to work with, if you mind a few things:

- the quality of the mold's surface matters
- it's damn heavy; make cavities
- stuff it with a lot of iron reinforcement
- avoid small details and sharp edges
- it requires much time to dry
- concrete can be easily sanded and filed
- apply concrete sealer on the surface

Concrete, combined with other materials, and painted, can acquire unexpected aesthetic qualities.