Introduction: Hanging Concrete Lamp

This is a semi failed but fun hanging concrete lamp. It was originally an attempt to slip cast concrete, which didn't work out so I ended up flicking and smoothing the concrete on. This gives it a rough interior and smooth sleek outer shell which is surprisingly strong but much thicker then the original slip cast that I wanted. 
I am new to concrete but am loving it so if anyone has ever done any slip casting with concrete I would love some tips. 

What you need:
Light fixture
ABS styrene 2.5mm
Hot glue
sand (fine grit) 
small piece of foam core

Step 1: Cutting the Mold

Print the two lamp guide templates onto A3 paper, and cut them out. 
Tape them down to your 2.5mm ABS styrene. 
Cut around each piece. You should have 5 pieces. 

Step 2: Making the Mold

Tape the pieces together. I found this easiest by taping on the straight edges first and bending and sticking them to fit with the curved edge. 
Because these pieces have just been blown up from a tiny test model and aren't from a CAD the top is not quite flush so I pushed it in to a small piece of foam core then hot glued around the top. This should create a flat top for the lamp.
Cut or drill a small hole in this foam core for the lamp's wire to thread through.
Cut a circle plug the same size as your light fixture out of the foam core and wedge into fixture
If your fixture has holes where the concrete can enter glue them up. Wire up the light fixture on the inside and pull to the top. (although I cast the entire fixture inside the concrete on second thoughts I should have only cast half of the fixture leaving the top of the fixture exposed to stop the build up of heat within the lamp and concrete.)

Step 3: Casting

What DIDN'T work: Slip casts
First I attempted a 1:2 concrete to sand mix which was on the runny side. So that I could pour it in to my mold and rotate the mold around, coating the walls with concrete. Unfortunately the concrete only left a very very thin layer on some areas of the walls which would never hold up, I thought that I could just do three or four layers to build up the strength but just from touching my mold the walls moved enough to crack the concrete. Again any ideas on how to achieve this would be great I really want to see if I can get the concrete so thin it glows with the light. 

What did work: Flinging and smoothing concrete.
With the slip cast lining the walls create a thicker concrete mix still 1:2 concrete to sand but less water than the slip mold.
With a trowel (piece of ABS) flicked the concrete on to the walls where it would stay nicely.
Using the same trowel(piece of ABS) smooth it out to the texture you are wanting for the interior. 
Leave to dry for 24hrs +.
Carefully demold and hang. 

Concrete and Casting Contest

Runner Up in the
Concrete and Casting Contest