The goal of this study was to develop a chemical treatment for limestone that would eliminate the repulsion, and thereby prevent salt from applying pressure on the pore walls. On the basis of screening tests, the polymer chosen for testing was polyacrylic acid with low molecular weight (~5000). Potassium hydroxide is used to raise the pH of the polymer solution to 7-8, and the solution is equilibrated with calcium carbonate before being introduced into the stone, where the polymer adsorbs on the pore walls. When crystals of sodium sulfate are induced to grow within the stone, the damage is strongly reduced by the coating in most cases. To date, there are problems of reproducibility with the treatment that are not fully understood. Possible explanations are discussed and additional research directions are proposed.
This research was made possible through Grant MT-2210-09-NC-03 from the National Center for Preservation Technology and Training (NCPTT).