In preparing a previously surface,

In preparing a previously surface, it is necessary to remove all corrosion and all paint which shows evidence of corrosion, peeling, excessive thickness, brittleness, blistering, checking, scaling, or general disintegration. It is essential that the removal of the old paint be carried back around the edges of the spot or area until an area of completely intact and adhering paint film, with no rust or blisters underneath, is attained. Edges of tightly adherent paint remaining around the area to be recoated must be feathered so that the repainted surface can have a smooth appearance. The remaining old paint should have sufficient adhesion so that it cannot be lifted as a layer by inserting a blade of a dull putty knife under it. The rate of blast cleaning may vary from one area to the next, in order to achieve the desired end condition.