I've applied Gypsum to my own lawn over the years (pellitized with sulfur) because of our heavy soils, also high in pH. Does it REALLY help to loosen up the soil and help water permiate better, or is it more myth than fact? Had a customer (HOA) call today and inquire about Gypsum for their lawns. They have ALL CLAY. It's nasty stuff, but the lawns seem to do well. I aerate every other year usually. I told her that one application is probably not going to give any sort of visiable improvements (and I don't believe that 2 years worth of applications would show either), but it's oe of those things that "wouldn't hurt to do". Of course the cost factor is there. At the recommended rate of 20 lbs per K. thats 1,400 pounds of gypsum I'd need for the one application.