I heated with a pit for several years, until I moved to New Braunfels. I prefered 2 to 3 inches of sand covering the pieces. Too little & pop. The heat will be too high. I found the speed in which I brought the rocks to temp was the greatest factor. Small flakes & spalls can be heated rather quickly, but larger chuncks need a lot more time to reach the desired temp. I will add I prefer the color changes in abo heating to roaster. Lots of luck. Tower