We're putting in a screened porch--a slab on a foundation. The mason just poured the trench footing and laid the first course of block today. So, there's all this dirt from the excavation, and he suggested using that instead of stone under the pad. He said it's cheaper and will work fine. He said we should still tamp it down. The soil does have a very high rock content. But I was Googling this, and everyone says use stone or you'll have major cracking problems. And it's a big slab--18'x24'. Is my mason crazy??