Controlling stress from salt crystallization

Salt crystals are able to exert stress on the pore walls in stone because there is a repulsive force between the salt and mineral surfaces, so that a film of supersaturated solution is in contact with the growing crystal. Damage from salt could be prevented if the repulsion were eliminated, so we have screened a variety of organic systems to find species that adsorb on carbonates and on salts. Several candidates were identified and tested for their influence on nucleation and growth of sodium sulfate; promising systems were applied to Indiana limestone, which was then subjected to cycles of soaking in sodium sulfate solution followed by drying. The treatment that offered the most protection was polyacrylic acid with very low molecular weight.