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Picture of Bent Concrete Side Table from a Rubber Mold.
This Instructable will demonstrate how to make a rubber mold for casting a bent concrete table. It will cover making a cardboard mockup, producing the positive, casting a rubber mold, and finally casting the finished concrete piece using a fiber-reinforced mix and bending it to shape.

This project was completed during the 3 day Advanced Fiber Reinforced Concrete Training at CHENG Concrete in Berkeley, California with guest instructor Chris Franzen from Surecrete. The unique characteristics of a fiber-reinforced concrete mix make it possible to cast a flat piece, wait until it enters a "false-set," and then bend the piece. For this we need a flexible mold, and in this Instructable we'll outline the steps needed to create a polyurethane rubber mold that will work for this technique.

Even if you aren't using a fiber-reinforced concrete system and bending concrete, the rubber mold-making steps are general enough to apply to any casting project.

Be sure to enter the Concrete & Casting Contest for a chance to win some nice prizes!
 
General Materials and Supplies:
 

In addition to having a good idea for an item to make, you do a wonderful job documenting and explaining the process. The instruction to make a mold would be good to have as a separate Instructable.

It also makes we want to get some of your blue pigment.

wow! I have to make it!

Stone_UFO1 year ago

that's awesome

trippy

So cool...
wow...
wow...
splatman2 years ago
The nice part about the rubber mold, is you can bend it, say, to a lesser degree, so the piece would be shorter and wider, or to a higher degree, to make a taller, skinnier piece. Or have the legs slope out, like in Cheng's example below, or make the legs wavy. Making the top concave is another possibility. A concave top can be used to hold a round object.
j_mark22 years ago
Oчень красивое изделие, но трудоемкое в изготовлении. ))) А почему бы не сделать 3 ножки ?
CHENG Concrete (author)  j_mark22 years ago
3 legs would be more stable, but 4 legs are stronger for the first test piece. At the same time we also cast a low table with 3 legs. Cпасибо за комментарий!
green_table_mold1.jpg
hay_jumper2 years ago
Anyone wondering how to write an Instructable should read this; Well documented, well written, and smart. Thumbs up all around.
Totally agree with that. I'd still say it's some magic I just saw here. :)
mkadri2 years ago
Lots of time and if u drop it will break not cheap
CHENG Concrete (author)  mkadri2 years ago
The concrete material used for this retailed for about $58 USD. The most expensive component of this instructable was the casting rubber which is roughly $8 USD per pound, but the rubber mold can be used to make hundreds of copies.
artworker2 years ago
freaking genius!
Ninzerbean2 years ago
Amazing! What ever gave you the idea to bend concrete?
nicko02 years ago
what type of fibers are in this gfrc
CHENG Concrete (author)  nicko02 years ago
The mix contains Glass AR, PVA and Nano fibers. Heavier fibers can be added to the mix, providing extra strength for using it as a structural backer.
james.m.k2 years ago
Wow! I was concerned that concrete would snap easily, making it a hazard to children and elderly, (and goofing adults) but I guess you answered that with the reinforced concrete. I find the bending of the concrete especially awesome! Blew my mind!

My only other thought is that it's heavy for indoor use, but maybe you could add crumbled foam bits to lower the weight.

It should be very nice for outdoor furniture. Though if you don't have other nice outdoor furniture to go with it, it will look out of place. Goodness knows it probably will never need to support 400 lbs!

Should make a handsome pot holder!
Oops, I meant to put the "Goodness knows it probably will never need to support 400 lbs!", after I suggested adding foam crumbles to the mix. :-))
Greenehouse2 years ago
Cool project, thanks for sharing it!
jwmock2 years ago
great job, great pictures and explanation!
simply awesome
linda602 years ago
how much all this will cost ??
studleylee2 years ago
Wild and very cool. thanks!!!!
jbarziza2 years ago
Thank you for posting this. I'd never heard of Glass Fiber Reinforced Concrete before. Many new things to look at. This was very, very interesting.
CandyLV2 years ago
I really dig the fluid pieces made from material known more for its immobility!
jon3laze2 years ago
Great instructable,what is the weight of the finished table?
CHENG Concrete (author)  jon3laze2 years ago
Thanks, the finished weight is right around 35 lbs.
phoe2 years ago
Nice instructable ! - I didn't know products like this existed, but they probably cost a fortune in the UK (if available at all)
mbonet2 years ago
Great project . How about plans to make a small wall mount Urinal out of concrete ?
ac-dc mbonet2 years ago
Wrong material, porcelain that's glazed won't absorb moisture and will be easier to clean.
zap19982 years ago
Amazing.
Horef2 years ago
holy gremlin snaps batman! this is awesome!
marc.cryan2 years ago
insane!
vdvoort2 years ago
Wow... I.. just.. its beautiful!!! love it! great instructable, hope I find the time and money to try this in the future.
Gregbot2 years ago
sweet!