Garage Slab

I'm planning on pouring a 24 by 24 garage floor. should I pour it in 12 by 12 sections, or one pour as my local concrete plant says I should? how long should I wait before pouring each section and should I separate them with anything? If I do it in sections should I pour the footing first and how should I tie the footing to the slab? Can I use concrete blocks for the footing and should they be filled? The ground slopes about 8 inches in the 24 feet of the floor.  you have a great site. thanks for the help.
Lots of questions - some I can answer , but others require local engineering advise.
  • 24x24 is too large.  It will crack.
  • 12x12 should be OK if the slab is at least 4" thick and reinforced with wire-mesh (centered) or #3 rebars.
  • If you pour the sections on different days you probably do not need any separation - they will not stick together.  If you pour the whole thing in one day you will have to either cut joints (with diamond blade saw) the next day, or use "zip strips" to create the joints.  Your local Home Depot should have what you need.
  • Cut joints should be at least 1/3 of the slab thickness (1/2 is better)
  • The normal practice is to leave the garage slab as a 'floating' slab.  That means that it is poured after the foundations are done and is separated from the foundations with 'felt'.  You do not tie the slab to the footing.
  • I cannot answer the question about the concrete blocks.  That depends on the soil conditions, the weight of the garage, etc.  Normally I would use concrete footings poured in trenches in the ground and reinforced with #4 bar at top and bottom.
  • The garage slab needs to slope towards the door (for drainage).  You probably need at least 1-2 inches difference between the front and the back.
  • Some points:
    • Get the best concrete you can afford.  I would go with at least 3500 psi.
    • Check if the soil in your area is corrosive (includes sulfates).  You will need special sulfate resistant mix for that.
    • Wet curing is critical for good looking functional slab.  Start 'misting' the concrete soon after it hardens on the surface.  Cover it with plastic.  Keep watering it for at least a week - the longer the better.
I hope that helps.

Make sure you get local advise regarding the footing...