In the summer of 2006 we insulated the unfinished crawl space under our entry way and living room floor. The walls were initially just brick and stucco. I used 1" R5 green board, and just nailed it to the wall. I tried one panel with liquid nails, but the wall surface was too uneven and dirty. The hardest part was digging some of the dust covered mounds of earth away from a couple of spots. I used a fan to provide air flow out of the crawl space while moving the extremely dry and dusty dirt. For the floor, rolling out 6 mil black plastic makes the job much more pleasant and provides a vapor barrier. Notice the tape 6" to 8" above the ground level. I plan to triple this insulation. The new smooth surface should allow gluing new insulation to the old.