My choice of material? Extruded styrofoam scraps, since I have a lot of them.
The "bricks" are approximately 4 by 8 inches, and will end up about an inch thick when poured. They're intended to be pavers that go on top of a concrete pour as the exposed surface. The concrete underpour provides the base strength, while the pavers are the more decorative surface element. I learned this trick from the construction happening at the apartment I lived in in the Gulag.
Last night was more of an experiment than anything. The scraps were going to be discarded anyway, so the only loss was time and a bit of propane. I was more looking for texture, since I've been researching rock texture pretty much every time I've been taking Sadie for walks-- the neighborhoods down lakeside are a bit more tony than my block, and many of them have stonework of various kinds. The nicest ones have a combination of real stone and stone veneer, though I've noticed more than a few real stone retaining walls that are suffering some real damage from freeze/thaw cycles, and it's the stone itself that's failing.
I've been able to recognize stamped concrete, even one installation of stamped concrete that was exceptional-- it took me three days to realize that it was stamped concrete and not granite pavers. The dead giveaway was the way that it cracked: had it been discrete pavers, it would have cracked on the seams; instead, it cracked through the body of the pavers.
There are basically three kinds of discrete pavers that I've seen. The first are formed concrete, which are the common ones you can pick up at 'Nards or pretty much any home improvement store. They're very regular, and look exactly like poured concrete, which isn't bad at all, and goes very well with a modern house design. They have a consistent color and shape that will even out and "newify" a space. On the downside, they have to be installed in such a way as to stay level, or they look really bad.
The second kind are clay-fired brick pavers, which although they look fairly regular have some differences in them, mostly color and a bit of texture. They can have an old-world feel to them, but tend to be very rigid in size and shape. And fired clay does tend to be more durable than concrete, but when it does break down, it goes to hell plenty fast.
The third kind is what I'll call recovered granite pavers. Most of what I've seen are scavenged from the road construction along Lake Street or various older city road construction, or they're recovered quartzite from old road cobblestones. They tend to be very irregular, roughly rectangular or square, larger than bricks. The best ones have been smoothed over from decades of road traffic on them. Tons of character, and they have a richness to them that brings a stability and solidity to the old neighborhood homes along the lakeside.
That's what I'm trying to reproduce in cast stone.
Why on earth would I do that instead of just getting granite pavers from somewhere?
Well, let's just say there is a reason that the granite pavers are really only prevalent in the neighborhoods of $500,000-and-up homes. And remember, I'm all about the illusion.
I'm also looking at reproducing slate tile for the inside of the porch. That may or may not happen; I had some pretty cool texture results last night, but I want to try some other textures before I make a final decision. I may just end up using it for more irregular fieldstone for the exterior walkways. The inside porch floor may need to be smoother than the textures I was playing with to fit the aesthetic that I have in mind.