Steve, if you are asking about painting Celotex or similarfiberboardproducts, you can do so, but with the caveat that unless you use a suitable paint, perhaps a lacquer primer/sealer such as BIN, you may get brown bleed-through of the material. ...
One form of roof mastic is a sealer or cement that is used on any area of the roof where water infiltration could occur, such as along the edges of the flashing, at seams and corners, and over nails and screws. It can come in buckets, allowing people to apply it with a palette knif...