6. SUMMARY AND CONCLUSIONS

The main function of stone consolidating materials is to re-establish cohesion between particles of deteriorated stone. In addition to consolidation requirements, a good consolidant should meet performance requirements concerning durability, depth of penetration, effect on stone porosity, effect on moisture transfer, compatibility with stone, and effect on appearance. These have been termed primary performance requirements as they are considered to be generally invariable, i.e., they are essentially applicable to all stone consolidants regardless of the specific use. Secondary performance requirements are requirements which may be imposed in addition to the primary requirements because of specific problems encountered at certain structures. For example, to require a consolidant to immobilize soluble salts in a stone would be a secondary performance requirement.

Stone consolidants can be divided into four main groups, according to their chemistry. These groups are inorganic materials, alkoxysilanes, synthetic organic polymers, and waxes. Selection of what material to use depends on many factors including the type of stone to be consolidated, processes responsible for the deterioration of stone, degree of stone deterioration, the environment, amount of stone to be consolidated, and the importance of the stone structures. An universal consolidant does not exist because many of these factors will vary to some extent from structure to structure. Therefore, the preservation of each stone structure should be considered as an unique problem.

Few cases of long-term success with consolidating stone structures were disclosed in this review. Some apparent success has been achieved in consolidating small stone objects, such as statues, which can be treated in a laboratory. Consolidants should be used on massive stone structures only after an appraisal has been made which considers the risk involved, the benefits to be realized, and the probability of success.