Some of you guys need to stop thinking about using the real thing in N-scale--it's not necessary and (as Ed says) textures in N-scale are REALLY small! You would have to grind down most of these materials into a fine powder (think 160 times smaller) in order to come close to scale. Securing it to your layout is a whole can of worms in itself. If it were up to me, I would use paint and/or powdered chalk to simulate the dusty, grimy environment you are after.