The back sidewalk is constructed of Oklahoma Thin flagstones. While they are cemented in place, there is still a need for some form of grout between the stones. We have been using a tan polymeric sand. It has washed out of some places and aged substantially since it was last put in, so it seems time to redo this.
First step was to power wash the stones which washes out the sand and leaves us with a clean, dry, space to fill.
We bought 4 units (at $21.98 each) of Sakrete 40-lb Tan/Brown Paver Polymeric Sand from Lowe's ($95.18 total, including tax). We found the easiest way to install it was to just pour it on the sidewalk and sweep it over and in the joints using a push broom. Then wet it down with a hose-end spray.