Next week we'll pour a footing for the garage addition. Most of it is 12x18, except 1 18' section that has a 12x18 base with a 8x24 stem wall on top, making the addition about 22" above the existing slab. I'll have to fill in the void in the middle of the new foundation with dirt/debris. Should the dirt/debris be compacted? What is the process and how long should the foundation walls cure before I fill, then pour the slab within the foundation? This is the same project that started with a new slab section in an old garage. Drawings, permits, demolition of extensive termite damage. My wife's car is still in the driveway and there is no wall on the back of the garage. Give me about 2 more months . . . Appreciate the help!