1 INTRODUCTION

Stone restoration is an ancient and vast discipline that encompasses the treatment of individual stone artifacts, outdoor monuments, and architecture. While the deterioration mechanisms, cleaning, and consolidation of stone have received much coverage in the literature, the practical aspects of loss compensation have received little in comparison. The vital role of appropriate compensation methods in the overall longevity of an object, and the potential risks and damage from faulty ones, are important to recognize.

The purpose of this article is to present a compilation of the considerations and approaches for loss compensation in stone. Treatments of sculptural and architectural stonework from both interior and exterior environments will be examined. The focus of the discussion is treatment methods that impart more than mere cosmetic reintegration of a damaged surface by offering not only visual but also structural unity. For instance, treatments such as masking a loss with a piece of Japanese tissue will not be described (Hatchfield and Marincola 1994).

The review begins with an outline of criteria to be considered when choosing a compensation method. An overview of the two main approaches—replacement with a stone or stone substitute, and plastic repairs which harden in place—follows. Different materials and techniques for stone fill are then described.

Two main bodies of literature: writings on architectural preservation and art conservation, serve as the basic foundation for this review. A general survey of the literature reveals that relevant articles in journals devoted primarily to architectural works significantly outnumber those found in the art conservation journals. Differences in terminology exist, for example the term “fill” used in the fine arts conservation literature, where the phrases “mortar repair” and “composite patch” communicate the same concept in architectural terms. If the literature is approached with a broad focus, a look at fill materials in glass, porcelain, ceramic, and wood conservation reveals methods and philosophies also directly applicable to structural fills for stone.

The selection of materials and methods for structural fills for stone must be tailored to the specifics of each treatment. Stone type, environmental concerns, and cultural context will influence the conservator's choices. Mineralogical variations of types of stone may require different approaches, and often the same stone in different environments may receive different treatments. Cultural biases and expectations inform treatment decisions as well: for example, works of contemporary art may require a different degree of visual reintegration of losses (Lowinger and Williams 1994) than that of neoclassical, classical, or ancient works, while the treatment of Asian works (Scheifler Marks 1994) may follow a different philosophy of compensation than Western works. Archaeological stone objects may require reassembly for interpretation or stabilization, or they may not as the case may be. In short, no one treatment is applicable in all cases. In many instances, multiple approaches are used in a single project, a fact that emphasizes the importance of context in the selection of appropriate methods and materials (Bongirno 1977).