Damaging effects of salt crystallization on a porous limestone after consolidation treatments

Abstract

Consolidation improves the cohesion of stones and preserves stone-built heritage. However, consolidation also modifies other characteristics that have an important role in stone vulnerability to salt crystallization, something especially important in porous limestones. This study evaluates the potential ability of alkoxysilanes and phosphate-based treatments (DAP) regarding short-term compatibility with a historic porous limestone. This potential is assessed by analytical methods based on porosity and pore size distribution. Furthermore, the potential regarding medium/long-term compatibility is evaluated by analyzing the tendency for salt entrapment behind the consolidated zone, an effect that can exacerbate salt damages.The treatments increase the estimated salt crystallization pressure within the pores, but the stone susceptibility is partially compensated by porosity drops, which are considered positive according to the method adopted. Nevertheless, the salt crystallization tests reveal that some treatments, with both families of consolidants, favor the deposition of salts below the stone surface. The development of subflorescences can cause catastrophic damages to stone. Untreated stone and stone treated with alkoxysilane-based consolidants of low dry residue tend to develop efflorescences, a much less damaging situation.The outcomes of the current research using sound samples point out possible catastrophic risks that can emerge at medium/long-term in real situations when stones are treated with consolidants due to poor compatibility of the consolidation treatments and provides important knowledge to address consolidation of damaged stones.