This study on the deterioration of the sandstone of the temples of Karnak (Egypt) confirms that it is caused by: the combined action of water, sun and salts. Due to the Aswan Dam, the basicity and the salinity of the water table have increased and accelerated the destruction of the stone. The French Egyptian study centre of the temples of Karnak has started a conservation treatment consisting in the removal of the salts with paper pulp. The method, applied first in 1982 by M. Claveau, has been improved by the author who describes in detail the application process on the south wall of the south portico of the Bubastides.