This idea has been a long while in the making. When I was working in Belconnen last year I was surrounded by examples of Brutalist architecture. Lots of concrete. Not a fan of the style myself, but I thought it would make a cool idea for a guitar pedal.
The first attempt at a concrete pedal enclosure didn't work out. I built a form with wood, then put in more wood to be the empty cavity inside the pedal. More small bits of wood where I wanted holes in the outside for knobs and jacks. Wire mesh was added for reinforcing the concrete, then the box got filled.
Once the concrete had set, the wood didn't come out of the middle. I tried drilling it out, pulling it out, but in the end it took the concrete walls with it. The aggregate I used in the mix was also too large, so it stopped the mix getting right down around the sides.
I gave up on the idea for a few months.
The second attempt involved a plastic box inside the wooden form, with concrete poured over the top. I used wire gutter mesh around the plastic box, to try to hold the concrete together a bit better.
Again, I had issues when trying to remove the bottom of the plastic box. In the end I had to cut the bottom out of the plastic, but the concrete has held together nicely. I'm undecided as to whether to put another plastic bottom on the pedal, and more concrete to completely seal it off. That's going to make maintenance impossible.
The holes for the knobs were too small, so I've had to drill them larger. This worked well up to the 14mm drill bit, which wasn't quite big enough... but then the concrete between the holes started to tear out with the 16mm drill bit. Bugger.
I've ground the surface of the concrete down a bit using a small grinder, but it doesn't have a real polished look. To do that properly I'd need to buy some special concrete hardener (50 litres of it seems to be the smallest quantity I could buy...), diamond polishing wheels, etc. The rough look fits with the Brutalist theme better I think.
In hindsight, I should have used white or black tape when covering things before pouring the concrete. I used yellow, and you can see bits of it sticking out here and there. Tacky.
The effect is the Aeons from Grind Customs FX, which is based on the Amptweaker Tight Metal distortion pedal. It's a super high gain heavy metal/thrash style effect. The amount of gain is ridiculous. You can breathe on the guitar strings and it comes out as a scream from the amp. Riley loves it.
So anyway, introducing... the Brütalist. With dots over the 'u', just to show that it's really heavy metal.