Technical note
Surface Preparation for Cold Galvanizing: Sa 2½, St 3 and Direct Metal Contact
A zinc-rich coating can only deliver galvanic protection when its zinc network reaches electrically conductive metal. Surface preparation is therefore part of the electrochemical design.
Evidence-based corrosion guidance
Read with the current GalvoKote TDS and project specification.
The coating guide is unusually direct on this point: without direct contact, galvanic action cannot occur. That changes how surface preparation should be viewed. It is not just an adhesion step. It is also an electrical-contact step.
Sa 2½ for high-performance steel preparation
The current product technical data sheet specifies ISO 8501 Sa 2½ blasting for steel where the coating is being used as a hot-dip-galvanizing alternative or for long-term corrosion prevention. Blasting removes rust and mill scale and creates a clean, rough surface.
St 3 and St 2 in galvanized maintenance
The same TDS matrix uses ISO 8501 St 3 power-tool cleaning for red rust, old coating and welded areas on galvanized surfaces, and St 2 hand-tool cleaning where only white rust is present.
Do not prepare early and coat late
Freshly prepared steel can flash-rust or become contaminated. GalvoKote’s coating guide advises coating before corrosion or recontamination develops, normally within four hours after blasting.
Related pages
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