A few nice grinding surface images I found:
Gray Wall Pattern
Image by shaire productions
By Sherrie Thai of ShaireProductions.com
Feel free to download and use these as a background for commercial or noncommercial projects. If you decide to use them, please let me know how it goes by sending a link or an image. Enjoy!
people
Image by Daniel Kulinski
Taken with Samsung NX10
The wall
Image by Daniel Kulinski
Taken with Samsung NX10