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T~z~~i~a~ iB~sl9etin ~~~ ~;~-~a ~~ <br /> ~, <br />i ,luiy :ooz <br /> <br />SUBJECT <br />Overr:oating Aged IPaant systems <br />PURPOSE <br />To discuss test procedures and criteria necessary to make decisions on overcoating (or not overcoating) aged <br />coating systems. <br />GEIIERAL <br />The success or failure of an overcoat system depends on several variables: <br />v Condition of existing coating system. <br />Geographic location (exposure conditions). <br />~ Surface preparation pror• to overcoating. <br />a Type overcoat system selected. <br />Determinine Condition of Existine Paint system <br />Whether or not overcoating is a feasible alternative to complete removal and repainting depends a ;rear deal on <br />the condition of the existing paint system. The amount of corrosion present, number of coats, adhesion to the <br />substrate, adhesion between coats and geographic location (exposure conditions) are all factors that need to be <br />considered before a specifier can make an overcoat or complete removal decision. <br />Corrosion: One of the criteria used to determine if an existing paint system can be effectively overcoated is the <br />extent of corrosion that has occurred. This can be evaluated by visual assessment using ASTM D 510 Evaluating <br />Degree of Rusting on Painted Steel Surfaces. ASTM D 610 cor?tains photographic reference standards that <br />illustrate the degree of rusting on a numerical scale from 0 to 10 where Rust Grade L0 indicates no rust and Rust <br />Grade 1 represents 50% rust. [n other words, a higher rating indicates less rust. Surfaces with 10% or more rust <br />(Grades 4, 3, 2 and t) are normally not considered candidates for overcoating. <br />Page 1 of 6 <br />