8 FUTURE RESEARCH

According to the recent survey of members of the American Institute for the Conservation of Historic and Artistic Works (AIC) by the National Center for Preservation Technology and Training on funding priorities in materials conservation, fill materials are among the top 10 priorities in conservation research (Derrick 1996). Much of what is known about the successes and failures of various structural fill materials for stone is anecdotal. Nonetheless, there are well-documented treatments that are 10 to 25 years old, and some very useful observations may be made regarding their successes and failures. More and more the challenges of re-treatment face the conservator, where previous efforts have permanently changed the stone into a composite material.

Despite the numerous methods that have been described, gaps in the present repertoire of appropriate structural fills still exist. Research focused on finding methods for stable compensations of translucent stone in the outdoors and for patching mortars for thin cracks and shallow spalls would be invaluable additions. Present methods for structural fills of stone could be improved by learning how to modulate and control the porosity of cementitious and polymer patching mortars (Ma 1995). Methods like the inclusion of microfoaming agents and other materials (straw, polyfilaments) could be further investigated. Research that adapts industrial methods like those used for producing multidensity foams could be utilized. Further study of existing and new commercial products for dental molding materials could prove invaluable. Increasing the UV exposure stability, and therefore the lifetime of polymers in mixes, is another important step for fills used in both indoor and outdoor environments. The addition of polymer stabilizers to synthetic resins used as binders may be appropriate for many treatments (de la Rie 1988). Stabilized polymer and UV-absorbing coatings for fill materials may also be found useful in prolonging their effectiveness. Understanding the quantitative effects that bulking agents have on impeding the yellowing of polymers and decreasing or increasing their strength could also have practical application in the field.