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Harm Reduction Notes for the COVID-19 Pandemic

Concrete Formula for small/medium size objects

- Wed, 18 Mar 2015 16:48:17 EST 7JSxEYqU No.6665
File: 1426711697231.jpg -(984167B / 961.10KB, 2048x1536) Thumbnail displayed, click image for full size. Concrete Formula for small/medium size objects
I am looking for a good concrete formula to pour into molds.
Currently I am using this: 2 parts portland-composite cement (CEM II), 1 part Sand, 1 part water.
I'm ok with the consistency of the mixture, it flows enough to be poured into the molds and it represents details well enough.

The problem I have with it that the surface is dusty to the touch, I'm looking for something that you can wipe fingers over it and they stay clean.
It should also be able to be done using common hardware store ingredients, and not be in the price range of specialized mixtures sold for this purpose.

The final project should be to make viable speaker enclosures with the concrete poured cnc machined EPS foam molds.
Any additives are fine as long as they are non-toxic and not expensive.

I've read about steel wool for instance.
Caroline Crungerson - Sat, 21 Mar 2015 19:34:55 EST a5xmRWEe No.6667 Reply
could be the nature of concrete, I don't know. Maybe you could finish it?
Eugene Brookforth - Sat, 21 Mar 2015 20:40:53 EST 7JSxEYqU No.6668 Reply
Yes maybe. I'm thinking about trying these blue coatings normally used for swimming pools.
I also have tried adding silica, and will be trying different grains of sand next week. All this is supposed to increase the strength of the concrete and I'm hoping it has an effect on the surface structure as well.
Simon Gunderwell - Mon, 23 Mar 2015 01:10:20 EST a5xmRWEe No.6670 Reply
I suspect you'll have to finish it because the internal needs of the concrete are different from the finished surface. Something that you know will bond well; pretty doesn't matter if it doesn't stick around.

I'm just speculating really, I have no experience with this but your thread was lonely :(
Oliver Hocklestock - Sat, 25 Apr 2015 14:41:17 EST crpd18/b No.6686 Reply
Old thread, OP did you ever consider wax paper?
Oliver Candleswatch - Mon, 04 May 2015 13:45:43 EST BxGNplro No.6689 Reply
Sounds like the concrete hasn't properly cured. You should look up immersion curing, especially since your water to cement ratio is below .4 which will cause a tendency for it to dry out. Long story short, after the concrete sets, you need to immerse it in water for a period of time for the cement hydration to complete. The amount of time will vary greatly on temperature/etc., but that should help you out I hope?
Molly Perryman - Sun, 07 Jun 2015 04:16:45 EST juI5Twgu No.6712 Reply
powdery feel is dried out concrete. concrete can be finished with stains too which can look quite fantastic if done right. most are water based, perhaps hydrate in a stain?
Molly Perryman - Sun, 07 Jun 2015 04:18:58 EST juI5Twgu No.6713 Reply
omg OPEE pls do like a batik technique with red and maybe blue dye. then use a polishing from 60-200 grit. maybe dye after? IDK lol

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