I cut the faux stone out of paper mache drink carriers. I used a 1 inch foam brush. I put 4 doubs of paint in a large plastic lid: white, raw sienna, burnt umber and the foundation gray. I mixed up two colors at a time and painted the edge of the faux flagstone, then layed it on plastic and painted the top. After the stones dry, I sprayed them three times with Patricia Nimocks matte acrylic spray.
Then take one stone at a time and glue it from one corner to the other. If there is a large space showing, cut one of the stones to fit in the space. Put paint on the cut edge. Glue the stones down with Wellbond glue.