93% vs 96% Zinc in Cold Galvanizing: How Much Does Three Points Matter?

Most cold galvanizing products sold online sit at 93% zinc. Ours is 96% in the dry film. Three percentage points sounds like marketing noise until you look at what the number controls: whether the zinc particles stay in electrical contact with each other and with the steel underneath. Here is the honest version of that difference — including where it does not matter.

What the percentage actually measures

On a technical data sheet, the figure is zinc content by weight in the dry film, not in the wet paint. A 93% product and a 96% product can look identical in the can; the difference appears after the solvent leaves. If a supplier quotes a percentage without saying "dry film", ask again — wet-weight numbers are always lower and not comparable.

Why products land at 93% rather than 96%

Zinc dust is heavy. Above roughly 90–93% by weight the paint becomes thick and hard to spray from a small aerosol can, and settling in the can becomes a real problem for retail channels. Formulators trade a few points of zinc for sprayability, shelf life and cost. That trade is rational for a can sold in a hardware store for touching up a gate. It is a poor trade for a steel structure that has to survive a coastal atmosphere for a decade.

Why 96% matters for repair work specifically

Repair of hot dip galvanizing is governed by ASTM A780, which requires the repair material to deliver protection comparable to the original layer. A hot dip coating is essentially pure zinc-iron alloy; a repair paint is the closest practical approximation. At 96% zinc in the dry film, the zinc particles remain in contact through the thickness of the film, so the repaired spot keeps working as a sacrificial anode — it corrodes first, protecting the steel, exactly like the surrounding galvanizing.

Drop to a lower zinc loading and the film starts to behave like a barrier coating with zinc filler: it still protects, but the repair spot becomes the first place to fail when the atmosphere is aggressive. On a coastal project that shows up as rust blooming from weld seams and cut edges two or three years in — the classic "the galvanizing was fine except at the repairs" complaint.

What else decides the outcome (and often matters more)

• Surface preparation. Sa 2.5 with 40–75 µm profile, applied within four hours of blasting. No zinc percentage survives oil, salt or mill scale — see our Sa 2.5 guide.
• Dry film thickness. 40 / 60 / 80 µm is the working range on our data sheet; 60 µm is the typical specification. Half the thickness means half the zinc per square metre, whatever the percentage says.
• Binder and adhesion. A high-zinc film that lifts at a scribe is worse than a slightly lower-zinc film that stays put.
• Topcoat where required. In C4–C5 environments and for colour stability, the zinc layer is a primer — seal it with the recommended system.

How to verify a zinc claim before you buy

1. Ask for the TDS with dry film zinc content, volume solids and density — the three numbers that let you check a claim.
2. Check the test standard behind any salt spray figure (ISO 7253, ISO 9227, ASTM B117) and whether the panel was scribed.
3. Compare coverage, not just price per kilo: a 96% product at 60 µm covers 0.316 kg/m² on our sheet; do the same sum for the alternative.
4. For repair work, ask whether the product is positioned against ASTM A780 — that is the language a galvanizer or an inspector will accept.

Where 93% is perfectly fine

For a garden gate, a scratch on a handrail, or a touch-up where appearance matters more than decades of protection, a 93% aerosol does the job and costs less. We would rather say that plainly than pretend three points change everything. The distinction is application: decorative touch-up versus corrosion protection on infrastructure, marine and industrial steel.

FAQ

Is 96% zinc the maximum?

No. Thermal sprayed zinc is essentially pure zinc, and inorganic zinc silicates reach similar levels. Among single-component, air-drying repair paints, 96% in the dry film is at the top of what stays practical to apply by brush, roller or spray.

Does a higher zinc content mean a longer salt spray result?

Not automatically — film thickness and surface preparation dominate. What the higher loading buys you is consistency of protection across the repaired area, including at edges and welds where films thin out.

Can I use a 93% product over a 96% coating?

You can, but you create a lower-zinc spot inside a higher-zinc system. On a project with an inspection regime, that is the area the inspector will flag. Match the surrounding layer.

Related Reading