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April 20 - April 26, 2015

What is the best method for preparing newly galvanized steel to be overcoated with an epoxy system?

Selected Answers

From Rahil Shaikh of Link Middle East LLC on September 7, 2017:
First and foremost, remove any oil and grease as per SSPC-SP 1; once the oil and grease are removed, blow it dry and lightly sweep blast.

From Guus Schmittmann of Zinkinfo Benelux on July 15, 2015:
There are two possibilities: sweeping or a chemical pretreatment with 6+chromate. Unfortunately, 6+Cr will be be forbidden after July 2017 in Europe.

From Empty Jasson of Haiphong on April 23, 2015:
Use detergent cleaning to remove oil and grease. Conduct fresh water washing to remove dustand other contamination.  Create roughness on the surface to increase adhesion with sandpaper (from 120 above) or light blasting.

From trevor neale of TF Warren Group on April 22, 2015:
As stated by Clyde above, SSPC-SP16 provides the answers and methods for preparing non-ferrous metal, following that with an alkali-resistant primer such as epoxy will ensure long-term adhesion and performance.

From Clyde Morgan of BURNS & McDONNELL on April 22, 2015:
I use SSPC-SP 16 (Surface Preparation Specification - Brush-Off Blast Cleaning of Coated and Uncoated Galvaized Steel, Stainless Steels and Non-Ferrous Metals). It addresses several issues not found elsewhere, including wet staining, chromates and blasting material hardness to prevent damage to the galvanized material.

From Tolga DIRAZ of CARBOLINE Turkey - Bursa Plant on April 22, 2015:
As we are coating professionals, I believe our first priority is to follow industry standards and collective recommendations coming from reliable sources like technical societies and/or opinions of industry gurus published in respected magazines. Therefore, I primarily suggest using ASTM D6386 and SSPC SP-16. The former is more general and the latter deals with brush-off abrasive blasting of galvanized material. (They are especially useful if you are writing a spec.) Also, it recommend you to read the following paper in depth:

From Simon Wadsworth of COWI on April 22, 2015:
In accordance with the paint manufacturer’s instructions as always! UK practice would be to use either a mordant solution of inhibited phosphoric acid commonly called "T-wash" to etch the surface before painting or, if a high build primer is used, low pressure sweep blasting to provide a profile of 20 microns depth.

From Francesco Colica of Colimet srl on April 22, 2015:
The fast and secure way is to remove surface contaminants and then to blast softly, remove dust and paint.

From Marco Antonio Alvarado Meneses of Sherwin Williams Perú on April 21, 2015:
I agree with Winson. Remove oil and grease according to SSPC-SP1. It is necessary to carry out "the water-break test"; then, sweep blast is advisable (fine abrasive and low pressure in order not to remove zinc). Remove dust by air blow down, and overcoat.

Oil and grease must be removed with a strong detergent, followed by thorough fresh-water rinsing. The entire area must be (high pressure) fresh water-cleaned  to remove salts and other impurities. When the surface is dry, sweep blast with a mineral abrasive to a uniform, rough surface for good coating adhesion. Remove dust and clean the surface prior to painting.

From Winson King of PennDOT on April 21, 2015:
Remove oil and surface contaminants by SSPC-SP 1;brush blast, SSPC-SP 7. preferably with fine garnet, remove dust, overcoat ASAP during same shift.

From Larry Muzia of Exceletech LLC on April 20, 2015:
Although there are several methods used in our industry, my vote is either let the galvanizing weather for several months or brush blast using a fine abrasive and a journeyman behind the nozzle who does not overblast and addresses 100% of the surface area with the blasting procedure. In the old days a vinegar wash ( 5% glacial acidic acid) was common; however, allowing the acid to dry created as many problems as it solved. These type of acid salts are hard to remove and will cause blistering and delamination if a coating is applied over them. Assuming an oil post-treatment was not used after the galvanizing operation, there are direct-to-new-galvanizing coatings on the market. These DTM coating are generally formulated to exhibit low film stress and therefore will provide some level of performance, remembering that the new galvanizing's top metallurgical layer has a very high initial pH and is very dense. Applying a highly cross-linked coating film over new galvanizing, one should follow caution to achieve adequate adhesion for proper service life.

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Tagged categories: Asia Pacific; Coating Application; EMEA (Europe, Middle East and Africa); Epoxy; Galvanized steel; Latin America; North America; Overcoating

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