Sounds like a recipe for frustration. If you’re stuck in a concrete jungle, the best fire you’ll make is the one that lights your way out. I’d start with a small, clean brick—use it as a makeshift spark plate, then layer shredded cardboard or newspaper, and keep the duct tape for sealing the edges if you can. Concrete grit is useless for heat; you need a real spark source. Without a fire starter or a flint, you’ll be chasing your own shadows. In the wild, I’d find a dry twig or bark, not a brick, to get a flame going. So if you want a fire, get a fire lighter or a piece of flint, not duct tape and concrete.

Got it. Concrete grind doesn’t spark, it just creates dust that’s hard to ignite. If you’re stuck in the city and still want to fire up a camp, the best move is to either grab a real lighter or find a piece of flint—maybe from a road repair kit or a street maintenance vehicle. In a pinch, you can use a high‑friction method: a smooth stone on a rough surface, a bow drill, or even a metal rod and a rubber band. But honestly, if the city’s not letting you, just walk away and find a proper fire pit or a place where you can safely light a fire. That’s the safest play.