Use of poulticing in desalination of masonry units – implications on salt-deteriorated structures

Cellulose poulticing is a widespread method of desalination in practice for removal of salts from ancient structures. Optimization of the process is essential, considering that poulticing/desalination is the prime step during the protection of existing structures in the coastal zones. Even though poulticing is widely used in European countries, it is not common in India, because the principle and efficacy of the method have not been studied so far for masonry materials in the ancient Indian structures with specific microstructure. The present study analyses the effect of cellulose poulticing in bricks considering the role of pore size in the substrates and the removal of different types of salts depending upon the pore distribution. The process was found around 74% more efficient in removing Na2SO4 than NaCl in materials with more micropores (pore size <1 mm), as demonstrated from scanning electron microscopy images and analysis of pore structure using mercury intrusion porosimetry on brick samples. Interesting results on the unsuitability of cellulose poulticing in certain materials and the reasons for the same were obtained, which are based on the predominant transport mechanisms for salt removal. The study would be a reference for initiating cellulose poulticing as an effective desalination method in the ancient structures of coastal southern India