One key to affordable natural building is to use low cost, locally available materials. Look especially for what others don’t want – things like ‘problem soils’, dredgings, ‘wastes’. This brick making video was the inspiration for this blog post. It explains how a company in the Philippines uses abundant, locally available materials to make brick. They use silt and clay that accumulates in rivers and reservoirs. Removing the silt and clay helps reduce flooding as well as provide low cost building materials for their bricks. The same material would work for earthbags, earthen plaster and tamped earth floors.
Other examples of low cost fill material for earthbags include: subsoil (also called fill dirt by excavators), clay, caliche, road base, crusher fines, crushed limestone, sand, scoria, pumice, gravel, dredgings (this includes silt and clay as explained above as well as crushed coral and sand from marinas).