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
Tape 
Hot glue
concrete
sand (fine grit) 
knife
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. 

Comments

author
perec3 (author)2017-01-17

Hi! Very nice lamp! I would like to try, but is it possible to download the template to print? Thanks!

author
cbehrendorff (author)2013-09-01

Use GFRC spray on coat. You should be able to achieve a rotomoulded effect. Just instead of spraying it, I obviously pour it in.

author
dneishtadt (author)cbehrendorff2014-11-22

Is that a specific type of gfrc? do you have any recommendations?

author
anjin12 (author)2014-06-10

What was the final weight?

author
hgriffin1 (author)2013-08-28

How about thinset tile mortar with some fiberglass fibers added? This mixture should be strong but have a little flexibility.... Just a thought... I haven't tried it.

author
HamishDudley (author)hgriffin12013-08-31

Hey that sounds like it could be a winning combination, I have so fiberglass fibers on order so now I need to go and find some thinset tile mortar.

author
poofrabbit (author)2013-08-31

Just wanted to say congratulations on being a finalists in the Concrete & Casting Contest! This was a fantastic instructable! Good luck!

author
HamishDudley (author)poofrabbit2013-08-31

Thanks.

author
debraderek (author)2013-08-30

i liked it

author
KemikalzAreFun (author)2013-08-25

It's concrete.. It's not meant to be thin. I mean you can try adding epoxy in after you have the concrete all mixed.. But idk how good it would work.. Idk.. Maybe that's a dumb idea :P

author

Yeah I know concrete isn't meant to be thin - but that is exactly why I want to make it thin. I hadn't thought about adding epoxy, do you know if the concrete still sets? I could even make a laminate with an epoxy coating . Thanks for the idea.

author
Labyrinth (author)HamishDudley2013-08-27

There are acrylic additives that should improve the surface finish and allow for thinner cross sections. I still don't think you'll get it translucent thin however.

Search "translucent concrete" for information on the "standard" approaches. I suspect but have not seen that replacing sand with very small glass or polymer beads might give you the effect you're looking for.

author
HamishDudley (author)Labyrinth2013-08-28

Wow that translucent concrete is pretty cool. I wasn't originally planning to get it that much translucency, aiming for more of a slight glow from a very thin layer. But it's pretty dam cool.

author

The concrete should still set, but I'm not entirely sure..
Even maybe the bondo brand resin mixed so that it dries really fast, and adding it in the concrete before the resin starts to harden. Then putting your thin layer on quite quickly. But That may be kinda tricky though.. Haha just brainstorming all the thoughts that come in x)

That's a very good idea.
woulda never thought of that one.

author

I think I got to head to the hardware store and pick up some resin to play with. I was also wanting to try adding fibers to strengthen the concrete but I think I have to order them.

author

Cool deal, let me know how it works! I enjoy to seeing the ideas come alive.
I guess I'm not exactly sure what kinda fibers your talking about..?

author
digitalia (author)2013-08-27

You might try adding clear acrylic gel to the concrete. Acrylic additives are also available in powdered form, and are used in mortars and grouts. This might increase the translucency of the concrete. As for fiber strengthening, scrim is also available in fiberglass and plastic (don't know whether it's PP or HDPE) which might have higher transparency.

author
Windsrock (author)2013-08-27

You could try jute scrim or something similar. It's used with plaster for reinforcing.

author
HamishDudley (author)Windsrock2013-08-27

Hey thanks for the idea, I have been looking into adding fiberglass fibers or plastic fibers into the mix to harden it. But the jute scrim could have some hidden light qualities which could be interesting.

author
HelmutHound (author)2013-08-26

Having it hang by the power cable is a very bad idea.
It reminds me of the Sword of Damocles.
If you had a stand or mounted some chain to it and an anchor in the ceiling it would be great!

author
HamishDudley (author)HelmutHound2013-08-26

Yeah your right I should have added a stand to the top. I also thought it would like cool wall mounted with a few metal rods.

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