i have to give an estimate for a wall to be built. I have built 100 walls in my day, but never the slate style, chip and fit, if you know what i mean. i have to go about 1 1/2' high x 20' long. do you use cement caulking for added stability? and how do you estimate how many stones you will need? with the brick style, its a simple measurement, this i'm not sure, due to the randome lengths of stone. thanks.