Abstract: A method for preserving porous structures, including masonry structures having embedded structural or reinforcing steel rods, applies liquid preservative material to an exposed surface of the structure and injects the material into the structure using the blasting force of a compressed air stream at high velocity. The apparatus for practicing the method includes separate manifolds having multiple outlet nozzles provided for the liquid material and for the air streams, both manifolds covered by a shroud. The manifolds and their nozzles are arranged so that, as the liquid is applied to the surface of the structure, the high velocity air forces or injects it into the interior of the structure, so as to coat the interstices of the inner porous structure including any reinforcing steel therein, the high velocity air streams acting as a fluid hammer. The preservation of the structures occurs without the need of disturbing, breaking open or repairing brick, concrete or masonry structures.