Masonry is construction made with units such as brick, block or stone, commonly joined with mortar.
What this means at your property
A masonry wall includes joints and connections as well as the visible units. Moisture may move through cracks, porous material or adjoining details. A surface stain does not establish which route needs repair.
What should be checked before applying a sealer?
Ask the assessor to identify the moisture source, joint condition and intended drying path. The proposed treatment should suit the specific units and mortar; a coating is not automatically a repair for movement or water entering elsewhere.