Alright along with several other projects going on, I am going to concrete the garage floor, currently it is very hard packed dirt. I am going to have to do it a section at a time using 2x4 as frames probably about 4ft by 4ft squares. Question is --since I do plan on occasion to drive a car in there-how thick does it need to be? Does it have to be pure concrete or can I layer in some rock to cut costs of the concrete down? And if I lay the frame down level, does the ground inside the frame Have to be level, or can I just let the concrete fill in a little deeper in some areas (we're talking less then 1/2inch difference). Oh and since it will be done in sections, do I need to leave any space at all between the previous section and the next one being poured (for expansion/less cracking ect.) Any advice would be great I'm on my own for this one.