Sealers are often specified to improve the weathering characteristics of precast panels, especially in urban areas where the building may be subjected to airborne industrial chemicals. Sealers can also help facilitate the cleaning and maintenance of the panels if they should become dirty. When sealers are used, they should be applied in the field, after all the joints are caulked, repairs are made, and cleaning is complete. Otherwise, it is likely that the panels will have to be recoated in spots, which could lead to inconsistencies in color and finish. Sealers are also a solution to remedy minor non-structural cracks in the surface of precast panels.