This Instructable will show you how I made a concrete top that is able to emit light using optical fibers. Fiber optics will allow you to create a unique and original piece that emits light without the use of bulbs and electronics. The concrete surface will not show any sign of light display capabilities making it surprisingly cool for those unaware of this feature.

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Supplies

Light:

RGBW LED Fiber Optic Kit
- 450 pcs or fibers
- Fiber diameter = 0.75mm
- Length = 3m
Scraper blade
Torch

Mold:

Melamine
Pink Foam
Needle
Drill bit 0.8mm to 1mm
Drill
Wood screws
Silicone
Circular saw
AquaCon mold release

Concrete:

GFRC Concrete Mix
Glass Fibres
Scale
Various size container to measure and mix
Mortar mixer
Concrete Pigment
Concrete sealer
Hopper Spray Gun
Air compressor

Step 1: Design

When using pigment, you get to pick the colour loading which affects how lighter or darker your final piece will look depending how much you add. I did a some samples with 2.5%, 3%, 4%, and 5% colour loading relative to cement weight. The wife liked a 3% colour loading so that's what you see on the finished product.

Step 2: Mold Making

The mold is designed to cast the piece bottom up so that the surface of the concrete takes the smooth texture from the melamine and the foam. The melamine and foam pieces are cut to size and holes are perforated on all faces to allow the optical fibers to be threaded through. There is no hole pattern, just space them however you like.

The mold is then assembled with the foam piece at the bottom of the mold and the side pieces screw to the side acting as walls for the mold. I applied silicone caulk to all edges of the mold to seal all gaps between the joined pieces. I then inserted all optical fibers through the holes and hang them on a bar above the mold to facilitate handling the fibers.I decided to create 4 bundles to contain the fiber within the piece as much as possible.

Step 3: Concrete - Mix & Pour

Using the volume figures from Fusion 360 model, I followed the GFRC mix instructions to prepare the necessary quantity of product.

The face coat will have pigment and no glass fiber while the backer coat does have the glass fiber for reinforcement and no pigment is necessary. The natural colour of my mix is white so the bottom of my piece is white while the top display the desired colour. You could colour both mixes but I decided to save on pigment used.

The face coat is sprayed with the hopper gun to the walls and bottom of the mold while being careful not to pull out the fiber optics. I then let the face coat dry for about 15 mins before adding the backer coat.

I poured the backer coat and filled the mould about half way. At this point, I worked the the optical fibers into the concrete and positioned the bundles at the back. I highly recommend doing this step which is bending the fibers into the concrete to avoid having optical fibers sticking out all over the back of your piece. Managing the optical fibers to stick out of the concrete in controlled bundles will allow you to keep things organized and neat.

I lay my foam fillers in place and poured the rest of the mix. The last picture shows the pocket created by the filler foams. I covered the piece with a plastic sheet to trap some of the moisture while curing.

Note: I highly recommend using GFRC ready mix since all ingredients come exactly proportionate in the same bag leaving you with just a few additional ingredients to add. This route was not possible for me since the ready mix bags available in Canada are very expensive. I created my own mix sourcing as many materials locally as possible and therefore, reducing the cost exponentially. I started with a basic GFRC recipe and adjusted accordingly until hitting the desired composition.

I decided to use GFRC to get a smooth and refinished surface that otherwise is hard to get with regular concrete. Weight was also a limiting factor since I did not want to upgrade my TV stand to a bulky furniture that would support a heavy piece as result of using regular concrete. The weight reduction and aesthetics is perfect for the look I am going for. GFRC is more expensive and more tedious to work with but the results are incomparable.

Step 4: Demould, Prep & Seal

I let the concrete cured for about 2 days before releasing it off the mold. In all honesty, this is the hardest part of the process; waiting patiently and holding in the urged to demould and see your piece.

I ended up with a few white spots on the surface of the piece by not mixing the pigment long enough for the face coat. Chunks of white concrete made it through my final piece. I was going to stain those spots with gray concrete stain but the wife opposed; she want it just like that.

Use a scraper blade and trim the optical fibers flush to the surface. I had the fibers stick out about an inch or two to reduce the chance of pulling out while pouring the concrete.

There was also a void along the side of the concrete piece that I missed when doing the pour so I decided to use a drywall screw as reinforcement and add concrete around it to fill the void.

I used a 50 & 100 grid diamond pad on a wet polisher to knock off the hard edges on the back of the concrete then flip the piece and used a 200 and 300 grid pad on the sides and top surfaces. You could also use an air sander or hand pads while adding water manually.

Apply the concrete sealer following the manufacturer instructions and let it dry before continuing. This piece will not be exposed to heavy stains like a kitchen counter top so the sealer is optional if all you expect is dust to accumulate on your piece. Regardless of stain protection, you may apply a sealer to make the colour pop or make your piece glossy. I used a matte sealer.

Step 5: Lighting

I used cable ties to bundle the fiber optics and straps at the back of the concrete piece to hold and route all bundles to the center of the piece. Looking nice and neat at this point.

I combined all bundles into one at the centre and wrapped it with electrical tape. I measure the desire length to reach the bottom of my TV stand and used a hot blade to cut like butter the optical fibers so they are all the same length. I added the metal ring that came with the fiber optics kit.

The last image shows a close-up picture of a optical fiber without light. The blueish colour is produced by the flash of the camera

The changes in light and brightness emitted from the optical fibers made it really hard for me to capture a video that would truly do justice to the amazing light show.The light engine comes with a remote control that enables you to change the colour of the light, the pattern and brightness as well as creating your own set-up combining colours and motion type.