The exteriors of many buildings require frequent refinishing. The use of an organic protective coating on these structures, many of which are of brick or convrete construction, is desirable for both the appearance and preservation of the structure. Within recent years, favorable attention has been attracted to the use of water-base paints on exterior masonry. Because of the great variety of surface conditions that prevail on masonry after several years of weathering, the use of such emulsions has not been an unqualified success. The random adhesive failure of some coatings applied to masonry buidlings frequently has marred the appearances of buildings and exposed areas of bare masonry within less than one year's service. A new primer-sealer has been developed for use on a variety of weathered masonry surfaces. It contains a commercially available material of isocyanate type which has previously been adapted to use as a bonding coat in the application of organic linings to the interior surfaces of large, concrete, fuel storage tanks. A program is in progress in which the isocyanate primer shows promise for use as a base coating on various masonry surfaces prior to the application of acrylic emulsion paints.