Originally published at: http://boingboing.net/2016/10/18/how-to-make-tiny-cinderblocks.html
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I wonder if it is possible to get a slightly rougher texture…It just doesn’t feel like a ‘real’ cinderblock without the unpleasantly rough surface provided by whatever aggregate material happens to be cheapest. And the irregularities have to be deep enough that even several coats of institutional-off-white paint can’t smooth them over.
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Speaking from direct experience, the hard part of this is indeed getting the plaster (or cement) mix right, especially in small batches. It’s quite easy to mix a whole bucket of plaster with the consistency of milk and very few bubbles (using the “islands” method), but if you’re mixing a small cupful you have to mix it by weight and stir it, which means lots of bubbles and usually, in practice, a thicker mix than you need. If you don’t have casting experience or a vacuum chamber, this project is a formula for frustration, especially with such a ridiculously small mold. 9 blocks don’t make much of a wall even if they all come out well.
That said, making walls from scale bricks is super-fun and looks amazing.
You could totally add very fine sand to get different textures, but bearing in mind that the mixing is already tricky and fillers will make it trickier.
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not so bubble free from the example on the left.
but a bit of green stuff (plumbers epoxy) and some paint will fix that. modellers are an odd bunch.
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textured paint after assembly into the whatever structure it is going to be used in.
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That does seem likely to be much more pleasant than trying to get a casting slurry with the necessary amount of rough aggregate to work in a mold that size. Might be cheating; but the sensible approach.
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Since its so small a diy vacuum chamber from a reversed bike pump might work. The chamber would also be fairly small so should be simpler than the ones for degassing pouring resins.
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I’d make sugar cubes.
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Would be interesting making a bunch of these and then building a scale structure with mini rebar and grout. Might also be a really good way for someone looking to get into construction to get some practice without having to build a normal sized wall or building.
Arkalite™ is an alluvial clay dredged from the Mississippi basin.
that is all.
You get practice by working under experience builders, not by building tiny buildings…
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I understand this 
i just think that building a scaled down model but still applying real building techniques might be a good way to problem solve and get practice. Also building tiny buildings sounds like fun.
you can always start with these guys…
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Fine pumice gel gives a fine gritty surface, though it may be too coarse for something this small.
ETA: Seems to me that concrete blocks are layered so that you can’t see the two empty spaces. So would it be easier to have 2 molds, one like this for any showing the holes, and another that is just a hexahedron for ones where you can’t?
I’m not sure you’ll actually be able to, considering the scale is way too big even for O scale, and anything over HO scale is nonsense anyway.
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