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188 SSPC-PS Guide 8.00 August 1, 1992 Editorial Changes September 1, 2000 SSPC: The Society for Protective Coatings PAINTING SYSTEM GUIDE NO. 8.00 Guide to Topcoating Zinc-Rich Primers 1. Scope 1.1 This guide covers the selection and application (including surface preparation) of topcoats to surfaces coated with zinc-rich primer. Both organic and inorganic zinc-rich primers are included. 1.2 The guide does not cover the selection and applica- tion of the zinc-rich primer. 2. Description 2.1 This guide represents good practice for topcoating zinc-rich primers as determined by industry consensus. It may not be applicable to all materials and conditions en- countered. 2.2 Zinc-rich primers are topcoated to provide ex- tended exterior durability in severe exposures; to improve color, gloss, and other appearance properties; and to pro- vide resistance to specific conditions such as highly acidic or highly basic environments. 2.3 Information on the use of one-coat zinc-rich paint- ing systems is provided in SSPC Painting System Specifi- cation 12.01. 2.4 DEFINITIONS: 2.4.1 Bubbling: The phenomenon caused by air or solvent vapors rising out of primer pores and being trapped because the topcoat has skinned over. 2.4.2 Burnishing: The polished effect that results from rubbing a zinc-rich primed surface. 2.4.3 Crater: A small bowl-shaped depression in a coating film. 2.4.4 Curing (cure): The process whereby an applied coating film achieves its ultimate physical and chemical properties. Cure time and dry time are generally not identi- cal, as curing may continue after coating is dry to touch. 2.4.5 Dry spray: The condition that results from the paint losing too much solvent before reaching the sub- strate. Dry overspray is a nonadherent form of dry spray consisting of discontinuous particulate, which occurs when dry paint particles are deposited on an otherwise accept- able surface. 2.4.6 Gassing: See Bubbling. 2.4.7. Mist coats: Very thin spray coats, usually about one-fourth of the required wet film thickness. The applica- tion of a mist coat prior to the application of a full topcoat is used to minimize pinholing, bubbling, and cratering of the topcoat system. 2.4.8 Mudcracking: A surface condition characterized by cracks that extend into the body of the zinc-rich primer. The appearance of the surface is that of a dried mud puddle. 2.4.9 Pinhole: A film defect characterized by small porelike flaws in a single coat which extend entirely through that coat and have the general appearance of pin pricks when viewed by reflected light. The term is generally ap- plied to holes caused by solvent bubbling, moisture, other volatile products, or the presence of extraneous particles in the applied film. 2.4.10 Primer: The first complete coat of paint of a painting system applied to a substrate. 2.4.11 Tie coat: An intermediate coat used to bond different types of paint coats. 2.4.12 Topcoat: The coating intended to be the last coat applied in a coating system. The topcoat is usually applied over a primer, under-coats, or surfacers. It is also known as finish coat. 2.4.13 Wash coat: A very thin, semi-transparent coat of paint, applied as a preliminary coating on a surface, which acts as a sealer or tie coat. 2.4.14 Zinc-rich primer: An anti-corrosive primer for steel incorporating zinc dust in a concentration sufficient to give electrical conductivity in the dried film, which enables the zinc metal to corrode preferentially to the substrate, i.e., to give cathodic protection. 2.4.15 Zinc salt formation: A non-uniform white dis- coloration on the surface of a zincrich paint produced by reaction of zinc dust with atmospheric constituents. It is sometimes referred to as “white rust.” 189 SSPC-PS Guide 8.00 August 1, 1992 Editorial Changes September 1, 2000 3. Reference Standards 3.1 The standards referenced in this guide are listed in Sections 3.2 through 3.3. 3.2 SSPC STANDARDS AND JOINT STANDARDS: PA 1Shop, Field, and Maintenance Painting of Steel PA 2Measurement of Dry Coating Thickness With Magnetic Gages Paint 20Zinc-Rich Primers (Type I - Inor- ganic and Type II - Organic) Paint 27*Basic Zinc Chromate Vinyl Butyral Wash Primer Paint 29Zinc Dust Sacrificial Primer, Per- formance-Based PS Guide 12.00Guide for Selecting Zinc-Rich Painting Systems PS 12.01One-Coat Zinc-Rich Painting System SP 1Solvent Cleaning 3.3 AMERICAN SOCIETY FOR TESTING AND MA- TERIALS (ASTM) STANDARDS: D 3359Test Methods for Measuring Adhesion by Tape Test D 4541Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers D 4752Test Method for Measuring MEK Resistance of Ethyl Silicate (In organic) Zinc-Rich Primers by Solvent Rub 4. Selection of Topcoat 4.1 IDENTIFY PRIMER: Proper selection of topcoats requires identification of the generic (chemical) type of primer. Often the specific product name is needed as well. First determine the class of primer in accordance with SSPC-Paint 20, which categorizes zinc-rich primers by the type of v

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