Plasters constitute an important component of many ruined architectural and archaeological sites. Methods for their in situ conservation have lagged far behind the field treatment of other materials due to their ephemeral nature and the lack of programmatic laboratory and field research. A preservation strategy involving documentation, stabilization, interpretation and maintenance offers a methodological approach adaptable to most contexts. A pilot conservation programme is described for the stabilization and interpretation of thelime plasters within the nineteenth-century adobe ruins of Fort Union National Monument in New Mexico. Methods of documentation, emergency stabilization, injection hydraulic lime grouting and mortar repairs are described.