There's A Hole In My Basement, Dear Liza

We've started ripping out part of the basement slab. It's a wopping 2" thick. It's so thin, I can break it with my 20oz masonry hammer. I drilled a bunch of holes 6" apart, and then used the masonry hammer, and a brick chisel (?) to make a straight line between them. Then I broke out the 16lb. sledge, although I didn't have to hit it hard at all. The part we're taking out is about 30'x6'. We knew the slab was in bad condition, the way it cracked when we were levelling the house. It would be nice to replace the whole slab, I don't think that's going to happen though, it's just too big of a job. If most of it has lasted this long, then it should be okay. We're adding a full bath, a powder room and a small kitchen, so there's lots of plumbing to do. I'm adding a step down at the back door as well, so we can have a full height door, right now it's only 5'-7", and I've hit my head many times.