I need to pour a concrete slab for a hot tub. I am waiting for manufactures recommendations on the size and strength of the mix. My other alternative is to mix by the bag. My question is that of preparing the area to be poured. How much should I dig out and what should I put in for a good base.....3/4 stone or gravel or both and if so in what order? I live in Masssachusetts. Would this effect the way it's prepared?