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February 12 - February 16, 2018

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

Selected Answers

From Alexandre Racine of Drytec Trans-Canada on February 15, 2018:
If you follow the SSPC-SP16 standard, the 'Chromate' test is described in 4.3.3. The test is required just in case the sweep blast didn't remove it all.

From Frank Rea of GPI - Greenman Pedersen, Inc. on February 14, 2018:
All good answers, but one important item has been left out. When it is known the galvanizing is to be painted, the specifications should be written and the galvanizing shop should be reminded at the pre-project meeting that no quenching or chromate treatment is allowed.

From Alexandre Racine of Drytec Trans-Canada on February 13, 2018:
Clean to SSPC-SP 16 with light abrasive (glass bead), 30-40 psi blast pot pressure with a large sweep blast method. Double check the galvanized thickness before surface prep. Read the epoxy specs for surface profile requirement to make sure it meets maximum galvanized surface profile achievement.  (If you need a 2.5 to 3 mils profile minimum profile, you will end up removing the galvanized surface). Check humidity level for white rust on surface. If so, wash the surface with proper detergent  after the blast. A pre-job meeting is a must to make sure the galvanized surface compliance meets the client requirements (galvanized dropping, over-thickness in corners). ASTM A123 accepts some surface criteria that sometimes don't meet client expectation.

From Michael Beitzel of Modjeski & Masters inc on February 12, 2018:
The answer depends on the type of galvanizing. Solvent cleaning and a sweep blast with less aggressive abrasive would be best for hot dip galvanized steel or fasteners. Solvent cleaning to remove lubricating wax and etching with a phosphoric acid and detergent solution would be best for mechanically galvanized surfaces. Both type fasteners and adjacent field should be primed with an organic zinc stripe coat to restore damage from installation.

From Erik Andreassen of CPS on February 12, 2018:
Prepare the surface by sweep blasting using a non-metallic abrasive such as garnet. Extreme care should be taken to avoid damaging the surface to be coated. Move the blasting nozzle rapidly just to create a key for the epoxy system.

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Tagged categories: Epoxy; Galvanized steel; Surface Preparation; Surface preparation

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