Standard · Metallic coatings and cathodic protection
ASTM D6386
Preparing hot-dip galvanized steel for painting.
Paint does not stick well to new galvanizing: the surface is smooth and carries zinc corrosion products and sometimes passivation treatments. ASTM D6386 covers cleaning the surface, then removing those products and roughening it, for example by sweep blasting or a chemical treatment.
The age of the zinc sets the preparation
- Newly galvanized: within the previous 48 hours.
- Partially weathered: zinc oxides and hydroxides have formed. They hinder adhesion and must be removed before coating.
- Fully weathered: a layer of zinc carbonate has formed. It is stable, does not dissolve in water and can be painted after cleaning.
Sweep blasting
Sweep (brush-off) blasting roughens the zinc without stripping it. SSPC-SP 16 asks for a profile of at least 19 µm (0.75 mil) on the bare metal, and the galvanizers' association adds that no more than 25 µm (1 mil) of zinc should be removed. For offshore systems, ISO 12944-9 also asks for galvanized steel to be sweep blasted.
Powder coating over galvanizing has its own standard, ASTM D7803.
2 practice items in the members area mention ASTM D6386 (CIP 2: 2).
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This page describes the subject of ASTM D6386 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ASTM International. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.