The more the better-from 3 to 4 inches up to 6 to 8 inches. A small amount of sand may do more harm than good. Enough coarse sand to make up 50 to 80 percent of the resulting mixture will improve the physical condition of a clay soil, if uniformly mixed with it. This is time-consuming and can be expensive. Calcined clay, the name given to clay granules fired at a high temperature, can be used the same as sand.
Calcined clay is more expensive than most homeowners are willing to pay.
This is one remedy for fine-textured soils high in clay content. The difficulty lies in doing it. Manure is out of the question, except on the farm where lawn soils are usually best. Compost can be used and is gaining acceptance as composting facilities are producing large quantities of high grade compost at reasonable prices. This will greatly improve its physical composition if you use enough peat.