2011-02
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 photo shows 5 samples of Cordova Cream limestone treated with amounts of PAA increasing from zero at the left to a layer about 10 nm thick at the right. The stones are standing in a bath of sodium sulfate, and were exposed to 39% RH for about 5 weeks.
Dear Dr. Scherer looking at the short abstract the application of the polymer would be done on new stone or stone that has had the soulble salts removed. Have you looked at pretreatment of salt removel that is done in the case of artifacts removed from the sea inviorment and soaked in DI water to clean the salt away or in bulidings where they use misting to remove drit and salts? This question is most likly for later work. I was also wondering about water vapor trasmition and if the polymer would add strength as a consoldant to a weak structure like old low fired brick. My last question is the polymer soluble after application and drying (ie) reversiablity to prvent bulid-up from several treatments. Thank You for your time and work. Sean Habgood