Painting galvanised surfaces
I have never painted a galvanised metal kitchen, but over the years, I’ve come across zinc-ed metal and learned the hard way that galvanised surfaces are tricky to paint. To save you some pain, these are a few tips I can pass along.
Use the correct materials.
I have found that painting metal can be a real waste of time unless it is done extremely well. And that basically means steering clear of DIY products like Hammerite and using specialist metal paints – plus a little bit of preparation, of course.
There is one stage in the spec for painting galvanised surfaces, which seems to be overlooked – etching – the first step in providing a grippy key for primer.
I was assured that the wind and rain can etch galvanised surfaces sufficiently well for primer to stick properly, but from experience, I don’t think that is actually the very best key. I have used a two-pack etch primer on galvanised fittings on a boat. It was nasty stuff, but, did it ever stick!
Crittal recommend zinc phosphate primer for bare galvanised windows. They should know, seeing as they make windows that last longer than the buildings they are installed in.
Back in the day, I was taught to degrease bare surfaces with white spirit, and use Calcium Plumbate Primer as a first coat. It was heavy, and lead, and expensive, but it seemed to work.
Zinc Chromate, the yellow one, was another primer used by some pros, but I have never used it because I thought it was for priming aluminium. Will have to check my college notes again.
There is obviously a conflicting choice for primers, but whichever one of the above you choose, they have to be better than any ALL PURPOSE primer!
Undercoat and topcoats
The best primers should be over-painted with a standard exterior grade oil undercoat and 2 coats of gloss. That spec works well.
Painting galvanised in century 21
Lead based primers aren’t in vogue and the modern paint system for galvanised surfaces from Dulux is Quick Drying Metalshield Primer plus two coats of acrylic Metalshield gloss. They claim 8 years between coats, which sounds a long time, I guess time will prove them right? I will find out all about it on a set of security gates next week, all being well.
Factory powder-coatings have to be the way to go for galvanised, if you have the choice.
Galvanised metal in marine environments
I had a few rusted steel mast bands to salvage. I had them shot blasted and re-galvanised with the hot dipping process. On site, I strung them up and applied a nasty 2-pack etching primer. Next day it had a bridging coat of chlorinated rubber-based paint, and then 3 coats of marine enamel.
Two years on, exposed continuously to the California sun, rain and sea salt, the paint on those fittings still looked as good as the day it was applied, albeit without the sheen. The secret I am sure is in the grippy surface provided by the etching primer, and the sheer thickness of paint on top. And 2 years on, the exorbitant cost of the materials was long forgotten.
Problems with painted galvanised surfaces.
One head scratcher: I have scraped back plenty of layers of flaking gloss paint from Crittal windows, and you think the failure is down to the last painter, who didn’t correctly prepare the previous coat of gloss. But when the paint layers come off in sheets to reveal the solid primer below? That would indicate that the undercoats didn’t have a good enough key to the primer. They possibly undercoated in the rain or on a very humid day. See, even using the correct paint for metal, if the weather is against you…
Repainting galvanised surfaces
If paint is failing on galvanised metal, I have found that the only sensible thing to do is strip back to the primer or bare metal and start again. Touching in chipped sections is not very satisfactory.
Having said that, when I cut my teeth on council jobs, (where I learned to get fast – not good at painting windows) the foreman never even had a tin of primer on site to touch in with. And the two pieces of sandpaper between 20 painters was too worn to feather off any chipped edges. Suffice to say, with painting standards like that around, uPVC windows were a must-have installation for council tenants’ peace of mind.
The symbol of galvanised metal architecture is the Crittal window. The company has far more experience than me about the whys and wherefores of keeping them looking pretty, so I would suggest visiting their website if you have a project coming up. And if you like to be royally entertained online, follow master tweeter @johnkatcrittall
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