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The authors characterized earthen wall materials and plasters in a mid-fourteenth-century Hohokam great house at Casa Grande Ruins National Monument (Arizona) and assessed the seismic susce...

Bandelier National Monument (BNM) was created to protect an extraordinary inventory of archaeological resources carved in the Tshirege Member of the Bandelier Tuff. These include more than one thousand excavated chambers, called cavates, used for dwelling, storage, and textile production. The glass-rich tuffs at the base of the Tshirege Member are poorly consolidated and susceptible to erosion by wind, rain, and mechanical abrasion, with resultant loss of cultural material. However, rock surfaces develop protective weathering rinds that are resistant to erosion. Using optical microscopy, SEM-EDS, XRD, and electron microprobe analysis, we determined that this rind consists of clay and silt sediments colonized by lichens and other surface biota, accompanied by the precipitation of secondary minerals in the near-surface pore space. Scoping experiments focused on glass-organic acid interactions indicate that oxalic acid excreted by microbial crust constituents catalyzes biogeochemical reactions that lead to the preferential dissolution of Si, Al, and Fe components of the volcanic glass; these cations become available for precipitation of opal, and smectite and sepiolite clays. Enzyme assays that quantify biological activity at outcrop surfaces indicate that microbial populations initially thrive as they derive nutrients from the dissolution reactions of the glass, but activity starts to decline as precipitation of secondary minerals limits access to new sources of nutrients, so that alteration processes are self-limiting. As case hardening progresses, imbibition rates at the surface decrease, and the erosion resistance of the altered surfaces is substantially improved. This article presents summary results of research conducted over a period of five years to characterize the roles of lichens and other microflora in rind formation, and the resulting contributions to tuff stability. The interaction of lichens and other microflora with rock surfaces in archaeological sites and monuments is usually explored in terms of biodeterioration and consequent damage. However, this study shows that, under some circumstances, lichens and microflora provide a level of erosion protection to relatively porous and unconsolidated rock strata that outweighs their biodeteriorative effects.

We have studied earthen plasters and wall materials from three ancient Native American sites in the American Southwest that include a twelfth-century, subterranean kiva used for textile production in Natural Bridges National Monument (Utah), a thirteenth-century, defensive, cliff dwelling at Montezuma Castle (Arizona), and a mid-fourteenth-century, puddled earth Great House at Casa Grande National Monument (Arizona). In each case, the data collected has been used to develop long-term preservation strategies and monitoring plans for each site. To understand the conservation issues, earthen materials were analyzed. Characterization included examination of BSE-SEM micrographs of polished thin sections prepared from a total of 36 samples from the three sites, and XRD of twelve samples. Research goals included: 1) determining the microstructure, micro-composition, porosity, mineralogy of aggregates and phases in the binding matrix for each sample; 2) reconstructing plaster technologies and their variation within and between sites, including material selection, preparation and application sequences, and; 3) identifying principal deterioration conditions and processes. Our findings support the idea that plaster materials were collected locally and manipulated to optimize their performance to suit the unique site conditions and needs of the ancient people using the structures.

Aztec Ruins National Monument is a World Heritage Site in northwestern New Mexico, USA. More than 50,000 visitors come to the site each year, specifically to visit West Ruin, a 12th–13th century, multi-storey Ancestral Pueblo an (Anasazi) village with over 400 rooms. West Ruin was excavated in the early 1900s and was intentionally left exposed for public access and interpretation. The walls, constructed of shaped sandstone blocks set in mud mortar, have gradually deteriorated, despite years of stabilization and preservation efforts. In 1999, park management began to partially rebury portions of West Ruin as a reversible long-term preservation treatment. While partial reburial allows for presentation of the site to visitors, it also results in uneven fill levels in many rooms. Differential fill levels can increase the area subject to migration and capillary rise of moisture through the walls, and can accelerate stone and mortar deterioration on the exposed wall faces. Differential fill levels can a...

The Laetoli hominid footprints in northwestern Tanzania are of major importance in understanding the evolution of humankind. The tracks are 3.6 million years old and pre-date the development of too...

A laboratory and field testing programme for the formulation and evaluation of hydraulic grouts was developed for the reattachment of lime plasters on earthen (adobe) walls. Formulations utilizing kaolin, hydraulic lime, ceramic microspheres, and fine silica sand, with and without the addition of an acrylic emulsion, were prepared and evaluated in a three-stage testing programme. Standard tests were employed to measure injectability, viscosity, set time, shrinkage, weight, splitting/tensile strength, water vapour transmission rate, and adhesive bond strength. Grout microstructure was comparatively examined using scanning electron microscopy. Of the 18 grout formulations tested, only one mixture composed of (parts by weight) 1 part microspheres, 1 part sand, 2 parts hydraulic lime, 10% part acrylic emulsion was found to meet all the essential performance criteria established.