[Richard Weatherby]

I didn't use the black foam. I use the regular foam. Note that there are differing expansion rates. The rocks are stacked and fitted in place before any foam. Don't over do it. It will stick to the surface of the rocks and take a long time to wear off. After it oozes out and cures, dig it out with a grapefruit knife. Then grout with precision grout in a bag. This is not my wife's pastry bag; they do sell these in HD or Lowes. I tint the grout with the black mortar coloring.