The University of Pennsylvania Architectural Conservation Laboratory, in cooperation with the Division of Conservation of the National Park Service Southwest Regional Office, report on treatment-in-place of plaster still adhering to the exterior and interior walls of adobe structure ruins. After selecting representative problem areas of two 19th-century military posts and laboratory testing of materials and methods, a pilot implementation was carried out in two seasons of summer field school work. Treatment involved temporary stabilization with Japanese tissue paper or cotton gauze facing applied with poly(vinyl alcohol), consolidation of paint with Acryloid B-72 in toluene and xylene, clearing cracks and edges as well as blind voids, grouting with a specially formulated mix, edging and filling, removal of facing, and surface cleaning. -- AATA