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Building small objects out of concrete Answered

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.

Discussions

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

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

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...

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.

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

Cool.

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

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

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.

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...

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