How to Coat Galvanized Media
The following information is intended as a guideline for the coating of hot dipped galvanized substrates where the end use requires a high performance exterior coating systems. Intended end use markets would include light poles, commercial industrial equipment, and agricultural implements.
ATP – Advanced Technology Primer: Anti-Chip Corrosion Resistant
|Primer Description and Powder Characteristics|
|Film Characteristics – Internal QC||PT Test||Reference ASTM Test for specifications|
|60 Deg Gloss:||PT-310.080||D523||50 +/- 5||Units|
|Flexibility (Conical Mandrel):||PTL-310.210||D522||1/8 PASS||@ 2.5 mils.|
|Direct Impact:||PTL-310.060||D2794||120||min. in lbs. @ 2.5 mils|
|Reverse Impact:||PTL-310.060||D2794||120||min. in lbs. @ 2.5 mils|
|Solvent Rub:||PT-310.070 (90/10)||50 Double Rubs||Softens, Recovers with Slight Loss of Gloss|
|Chip and Corrosion Resistance - ATP Primer + Pentabond Topcoat||Typical Test Results Generated: 2005 – 2007|
|Gravelometer:||D3170||5B – 7A||ATP + Topcoat 5- 10 Mils|
|Post Gravelometer Corrosion||D3170B117||No Adhesion Loss||2,500 Hours Salt Fog Exposure|
Pentabond TGIC Polyester Topcoat – AAMA 2604
|Environmental Performance Characteristics|
|Solvent Rub:||PCI #8 Reagent B||50 Double Rubs||Softens, Recovers with Slight Loss of Gloss|
|QUV:||PTL-310.320||G154||2500 Hours Typical||50% loss in gloss|
|Chalk Resistance, South Florida||D4214D659||5 Year Exposure||8 Rating, Max|
|Fade Color Change, South Florida||D2244 S6.3||5 Year Exposure||Max 5 Delta E|
|Gloss Resistance, South Florida||D523||5 Year Exposure||Minimum 30% Retention|
|Humidity:||D2247||1000 Hours Typical||No Blistering, or Discoloration|
Substrate Preparation: Hot Dipped Galvanizing
The objective is to remove oxidation, soils, and provide an adequate profile for film adhesion.
Step 1: Prepare substrate per ASTM D7803 -12 (2012) Standard practice for preparation of Zinc (Hot Dip Galvanized) coated iron and steel product and hardware surfaces for painting.
Step 2: Grinding of Surface Defects. Any remaining surface defects should be ground and the immediate area air blasted.
Step 3: Final inspection to be completed and approved by a trained operator. A suitable surface profile gauge should be used periodically to insure an appropriate surface profile is achieved.
Step 4: We suggest preheating the substrate prior to coating to prevent gassing. Allow the substrate temperature to cool to between ambient and 200° F before applying the primer.
Note: Any additional cleaning and conversion coating after surface profiling is acceptable and encouraged. For additional guidelines, please contact either your chemical pre-treatment and/or pre-treatment supplier.
Application of Primer: Please refer to the link "How to determine powder coating curing". This document details the proper application and cure determination in order to insure maximum inter-coat adhesion between the primer and topcoat.
Application of Topcoat: The topcoat should be applied immediately after the priming process is completed. For optimal transfer of powder topcoat to primer and substrate, part temperature should be above ambient and below 200F. Once primer is applied, any delay in topcoat application may result in surface contamination of primer film that could result in defects of topcoat. The Cure Curve chart below should be used in order to achieve the desired properties of the topcoat applied. All PTI Pentabond topcoats follow the parameters outlined below. Final cure testing of the topcoat needs to be performed using the PCI #8 test method. This is a destructive test method so an inconspicuous spot shall be selected.
Cure Curve – Substrate Temperature
|Cure Curve - Substrate Temperature|
|HANDLING||Do not use near sources of ignition, spark or open flame. Store in dry area below 80 °F away from all sources of heat.|
|PRECAUTIONS||Provide adequate dust control and use approved dust mask. Avoid skin contact. Wash with soap and water if contact occurs. Use only in well ventilated areas. Wear proper eye protection.|
Finished Coating Maintenance
Regular cleaning and maintenance will extend both the decorative and functional service life of a coatings system. It is suggested that the coated item be cleaned and maintained annually, at a minimum. If the item is exposed to heavy duty use and/or contamination, this frequency should increase in order to maximize the coating life cycle. Specifically, if the item is located in a geographic area where road salt is used, annual spring cleaning is highly recommended.
Surface cleaning should be accomplished using non-abrasive cloths or brushes in conjunction with warm water and a mild detergent. For removal of heavy deposits of salt, a citric acid cleaner may be used. A citric acid concentration of 10% should not be exceeded. For removing grease, oil, or other hydrocarbon deposits, the use of mineral spirits is suggested. Stronger solvents should not be used.
After any cleaning, the item should be thoroughly rinsed with warm water.
Repairing – Field
Surface preparation will depend on the degree of damage to the coated item.
For cases where the damage has not penetrated to the substrate, a medium-fine grit sand paper should be used to scuff the surface prior to priming. A high quality air dry surface primer should be applied, followed by an air dry topcoat matched to the color of the original coating.
For cases where the damage has penetrated to the substrate, a wire brush should be used to remove any remaining loose film and abrasion of the substrate should be completed. Use a medium-fine grit sand paper for final prep. Priming and top-coating should be prepared.
Note: Performance of the field repair in most cases will not be equal to the original coating system. Specifically, unequal fading of the repaired section compared to the original coating system should be expected, along with decreased corrosion resistance. The higher the quality repair paint, the better.