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Coastal oxidizing on galvanised painted surface

March 9, 2008

Hi

I as a typical South African love the outdoor life and have a coastal holiday home. Its all great to have a home at the ocean however as we know the salty sea air is a destroyer. I have an entertainment balcony with beautiful balistrades which I had galvanised to prevent rust. I have had them painted only to find that within days I get white oxidation (white rust?) forming on the surfaces, I heard of a Belgian paintcoat product which before application requires surface cleansing, degreasing, blue and black stopper applications and then the specialised surface finisher. Looked great but two months later we are back to square one. Its all turning white again.
Any solutions out there?

Paul Kakebeeke
- Somerset West, Cape Town, South Africa

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March 13, 2008

Its interesting that you say you have white rust on painted galvanized steel, but you don't say if the paint surface is broken?
Is the white deposit on the surface of the paint, or between the paint and the zinc?

Plain galv will go white quite quickly under these conditions, and thats normal. That white deposit is then what protects the steel and the remaining zinc. That how Galvanizing protects. Its not the zinc so much as the zinc oxides and carbonates that are protecting, with underlying electrolytic protection by the zinc.

We had a similar case recently with powdercoated galvabized balconies at a seaside house. White deposits appear after every storm, strong wind etc.
On inspection, what was claimed to be faulty coating, was found to be dirtly coating. The surface was encrusted with salt. (quick taste test suggested this, and analysis of the white powder scraped off confirmed).
Remedy: wash the salt off with water. Problem solved.

Your case might not be the same, but you haven't given quite enough info to tell. But all paints are porous to a degree. Could be salt water penetrating the paint, reacting with the zinc, producing white dust.

Is the paint cracked? Is the deposit on the surface of the paint?

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK