Question 12: What type of material should be used to backfill?

Granular materials such as rock and sand are best if available. These types of materials compact fairly easy and won’t hold moisture that can increase the weight of the soil behind the wall. Keystone walls can be effectively built with silty material and lean clays, but these types of soils require more compaction and care should be taken not to place these materials when they are wet. High clay soils that shrink and swell rapidly as well as organic soils should be avoided.