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Building small objects out of concrete Answered

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Hi all,

I was wondering if i could get any pointers on mixing concrete, I have gone through the concrete mixing instructables already and have not found anything suitable and hence I am asking her. I want to formulate an open recipe to make concrete objects like the ones in the following links,

http://fancycrave.com/concrete-desk-accessories/
http://www.ledindon.com/en/objets-design/9029-stylo-plume-beton-arme.php
http://www.designboom.com/design/concrete-rollerball-pen-by-22-design-studio-at-designboom-shop/

They are mostly small objects where the wall thicknesses are quite small (maybe a few mm). I think it will be interesting to see a DIY approach to making a concrete composition that is strong in small thicknesses, i think a lot of cool objects can be made from it .

I have tried the normal concrete mix with cement and sand but i am not able to get it strong enough at those small thicknesses. Can anyone please some suggestions or advice on how to go about this ? 

Thanks in advance, please see attached files for some images taken from around the web, i do not own any of them.

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CaseyG39 (author)2017-01-21

This is what I use! ShapeCrete, plays like clay works like concrete.

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user

I'll have to have a look at that stuff, looks interesting!

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varun2021 (author)2013-08-30

I am also looking to add powdered glass, and steel wool bits to the concrete mixture, would that be of any help ?

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Kiteman (author)varun20212013-08-30

Oh, that sounds promising. You'd have to seal the concrete to stop the iron rusting, but with enough glass in the fill, the concrete could become translucent...

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varun2021 (author)Kiteman2013-08-30

That sounds interesting, ill post an instructable with my findings, i am going to try out : glass powder, glass wool, steel wool, silica and nylon powder/fibers.

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MarkW11 (author)varun20212017-01-20

Hi, wondering if you came up with a solution since I'm exploring this at the moment.

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Kiteman (author)varun20212013-08-30

Cool.

Remember to take plenty of photos, and record how much of each substance you add.

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mikeasaurus (author)2013-08-30

There's a few GFRC (fiber-reinforced concrete ) that might be what you need, here's a project that was recently done with GFRC: https://www.instructables.com/id/Fabric-Formed-Tea-Table-in-GFRC/#step6

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varun2021 (author)mikeasaurus2013-08-30

Thanks for the link, but unfortunately I asked around and GFRC is not available to purchase where I live

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Kiteman (author)2013-08-30

Try changing the filler for something much finer, powdered rather than grains (talc? Ashes from a fire?), or fibrous, such as scraps of paper or shredded fabric.

You will also need to makes sure absolutely all the air is out of the mix - tiny bubbles that are fine in a concrete block will be fatal in a casting only a couple of millimetres thick.

Vibrate the mold, or put it in a vacuum chamber to draw the air out.

Hope that helps.

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varun2021 (author)Kiteman2013-08-30

Thank you for the suggestion, but i have tried just pure cement, there were not any air bubbles (as far as i could see) but still it was fragile...

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Kiteman (author)varun20212013-08-30

That may be the trouble - concrete needs the filler for strength.

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