
NPS
The building addition was created using a technique called "rammed earth." Building a rammed-earth wall involves compressing a damp mixture of earth that has suitable proportions of sand, gravel and clay with an added stabilizer into an externally supported frame, creating a solid wall of earth. Rammed Earth construction here consists of using native soils, quarried from near Casa Grande Ruins National Monument, amended with Portland cement, plasticizer and soil coloring. The mix is much drier than the "mud" that is used in adobe or in the caliche to build the Great House. The Rammed Earth construction method allows for the addition of new higher layers once the bottom layers are sufficiently packed. Damp material is poured in to a depth of approximately 10 to 12 inches and then compacted to around 50% of its original height. The material is compressed in batches, gradually building the wall up to the top of the frame. Tamping was historically done by hand with a long ramming pole, modern construction is more efficient employing pneumatically powered tampers.