Siloxane resin based product dissolved in solvent characterised by high capacity of penetration into the support. The product does not form a film, therefore it does not modify the water vapour permeability of the treated surface. It protects the surfaces from the aggression of atmospheric agents, notably limits the development of saline efflorescence and prevents moss, algae and mould forming. It strongly limits the absorption of humidity and consequently increases the durability of the construction.