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:

Step 1: Full Size Mockup

Look for Inspiration:Constraints of this project:
  • Cut out from a single sheet of 4' x 8' melamine
  • Minimum of 2.5" width of legs (for strength)
  • Thickness of concrete will be 3/4" (same thickness as the melamine that the rubber mold is created from)
  • Shore hardness and thickness of mold rubber will determine the radius of the bends
After deciding on a direction, sketch out some ideas. Cut out small paper models to test ideas quickly. Then create a full scale mockup from something like paper, cardboard, or sheet plastic. Change proportions as you see necessary. The first mockup for this bent concrete side table didn't have enough usable area on the top, so the second version was made a few inches wider in the middle.

Take your time during this phase while it's still easy to make improvements.
<p>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. </p><p>It also makes we want to get some of your blue pigment.</p>
<p>wow! I have to make it!</p>
<p>that's awesome</p>
So cool...
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.
Oчень красивое изделие, но трудоемкое в изготовлении. ))) А почему бы не сделать 3 ножки ?
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!
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. :)
Lots of time and if u drop it will break not cheap
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.
freaking genius!
Amazing! What ever gave you the idea to bend concrete?
what type of fibers are in this gfrc
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.
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! <br> <br>My only other thought is that it's heavy for indoor use, but maybe you could add crumbled foam bits to lower the weight. <br> <br>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! <br> <br>Should make a handsome pot holder!
Oops, I meant to put the &quot;Goodness knows it probably will never need to support 400 lbs!&quot;, after I suggested adding foam crumbles to the mix. :-))
Cool project, thanks for sharing it! <br>
great job, great pictures and explanation!
simply awesome
how much all this will cost ??
Wild and very cool. thanks!!!!
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.
I really dig the fluid pieces made from material known more for its immobility!
Great instructable,what is the weight of the finished table?
Thanks, the finished weight is right around 35 lbs. <br>
Nice instructable ! - I didn't know products like this existed, but they probably cost a fortune in the UK (if available at all)
Great project . How about plans to make a small wall mount Urinal out of concrete ?
Wrong material, porcelain that's glazed won't absorb moisture and will be easier to clean.
holy gremlin snaps batman! this is awesome!
Wow... I.. just.. its beautiful!!! love it! great instructable, hope I find the time and money to try this in the future.
sweet! <br>

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