Senior Airman Omar Portillo, 28th Civil Engineer Squadron structural technician, applies grout to a bathroom tile floor in the 28th CES operations building on Ellsworth Air Force Base, S.D., Feb. 21, 2013. The grout must dry for 24 hours before the tile is cured to guarantee the floor is a flat, clean surface that will last years longer than the previous vinyl flooring. (U.S. Air Force photo by Airman 1st Class Kate Thornton-Maurer/Released)