Peter, clay loam soil already has sand in it, and it also has silt. Google "soil triangle". So you just have to add enough sand to turn it into loam or sandy loam soil. In my very dense clay loam, 1.5 inches is enough. If you are starting out with pure clay soil, such as subsoil clay, I don't recommend trying to amend it. Either pile good soil on top of it, or truck it off the property and replace it with good soil. If your native soil will grow a good crop of weeds, it's probably good enough to amend with coarse sand. I've gardened on the east and west coast, and I've never seen soil turn into concrete because of the addition of sand. If you are worried about adding sand, buy a bag or two of coarse sand at Home Depot, and mix it into a small area of two square feet or so of garden soil. You will notice several changes: the soil will dry out and warm up earlier in Spring; seeds will germinate that never germinated in the clay loam soil; it will be very easy to pull weeds; the soil will not crust and harden and crack when it gets dry. But the most important change is that just about everything will grow very well in the amended soil, and you will not have the losses during the winter that you have in heavy soil. After four decades of gardening, I've gotten to the point where I refuse to garden in heavy soil. I just do the soil improvement up front before anything gets planted. I believe heavy soil is one reason why a lot of people give up gardening after a couple of years. You can improve it somewhat with organic matter, but it is a slow and endless task. With sand, the improvement is immediate and permanent. If you are in the Longview, Washington area, drop by and see for yourself.