How do I put a durable, protective coating on zinc plated steel

[JacKam_]

Two weeks ago I removed all all paint from my CR100/B28 front panel. As the result I got shiny piece of steel,with engravings, without any rust. I sanded it with 400 paper and painted with thin layer of Hammerite "red oxide primer" and left for drying.
Today I sanded it again for nice surface and sprayed a first coat of blue finish. New paint dissolved the Hammerite; it looked so bad, that I had to remove both layers to bare steel again.

My question is : How to put a durable, protective and nice coating to zinc plated steel ?

BTW, silver (they do not make grey aerosol) Hammerite (8 years protection) spray on zinc plated chassis looks OK, and I am going to paint my chassis after I soldered all ground connections.

Thank you,

Jacek

[David G4EBT]

I'd suggest that you'd be better off using an acid etch primer, which bonds itself physically and chemically with the metal. Really, two-pack acid etch primers are more effective than single pack aerosol ones, (which have a lower acid content) but for DIY use, U-Pol 'Acid 8' etch aerosol primer seems to be highly regarded. For illustrative purposes, here's a link to it at Halfords. (I'm not suggesting you buy it from there - you'll most likely find it cheaper on e-bay), but it will give you an idea of what it is:

http://www.halfords.com/motoring-tra...-8-etch-primer

There's some helpful information about acid etch primers here:

http://www.phoenix-paints.co.uk/abou...h-primers.html

I can only assume that the primer that you used wasn't compatible with the top coat. Nowadays, there is a move away from cellulose-based paint to water-based acrylics (most cars are sprayed with water based acrylic paint). I don't think cellulose and acrylic paint go well together - you'd need to make sure that you read the small print on the can of the primer and the top coat to see that they're compatible with each other.

Hope that helps a bit.

Good luck with it Jacek - it's a bit dispiriting when these setbacks arise.

[stumted2]

Hi Jacek,
It sounds like the Hammerite is oil based, and the solvents in blue top coat you used attacked/cockled/blistered the Hammerite.
Aerosols I would think are acrylic or cellulose types, and you can apply oil based over cellulose/acrylic, (though not recommended) but not the other way round.
I would check to see if you could purchase etching primer, followed by your top coat, as long as the primer is not oil based.
A good source of info can be obtained from H.M Guest Paints in Manchester.
Hope this is of some help.
Cheers, Ted.

[PJL]

I found a very close match from the standard Halfords paint selection but as this was 15 years ago the cars it was designed for will now be scrap. Just take a chassis with you and compare against the current paint range - as I recall the Leak paint is not metallic.

[JacKam_]

Thank you, David, I have learned something today and I believe that even DYI paints are better today than 70 years ago, so my receiver will look good for the next 100 years ,
Best regards,

Jacek

[David G4EBT]

Originally Posted by PJL

... as I recall the Leak paint is not metallic.

A bit of confusion has crept in - Jaycek is in fact re-spraying a CR100/B28 vintage military radio - not a Leak amplifier.

Same topic - different equipment.

Maybe the thread should be split off?

[stumted2]

Hi Jacek.
As I was typing this, the excellent advise from David, (whom I very much admire and respect, and who is a great source of information) posted, and I would thoroughly recommend his advice and think that this is probably the best way forward.

Just to add, that in my last post it was David G4EBTs post I was referring to, but it goes without saying, that all the advise I have had the privilege of receiving from all forum members, has been absolutely fantastic.
Cheers, Ted.

[AC/HL]

Thread split as suggested, thanks David.

[paulsherwin]

Originally Posted by JacKam_

I have learned something today and I believe that even DYI paints are better today than 70 years ago

That is highly debatable. Cellulose spray paints are now largely unobtainable in the domestic market, and even professional paint shops have to jump through hoops to use them. Acrylics are very difficult to apply using normal consumer spray cans, even for somebody with years of paintshop experience. Acrylics are also generally less durable than cellulose.

That said, your finish should have a good life if it is stored properly. The challenge will be to make it look good (and 'right').

[stevehertz]

My question is : How to put a durable, protective and nice coating to zinc plated steel ?

Just use the Hammerite straight on to the prepared metal, it's quite capable of being used in that way. I too have had red oxide primer bubble in the past.

[frankmcvey]

Concur with Steve - Hammerite doesn't seem to live with other paints, but it's designed to work without an undercoat. Same problems can occur if you try to cover it with a protective clear lacquer. Don't ask me how I know this!

Further to Paul's comments - cellulose lacquers are getting harder to find, but many luthier suppliers still stock them for guitar work, in a limited range of colours. You might want want a Fiesta Red or Lake Placid blue finish on your Stratocaster, but not necessarily on your vintage chassis!

Cheers,

Frank

[Skywave]

Originally Posted by paulsherwin

Acrylics are very difficult to apply using normal consumer spray cans, even for somebody with years of paint-shop experience.

That really took me by surprise. I have been using Halfords acrylic-based spray paints for several years now without any problems at all. And I am not "somebody with years of paint-shop experience".
That spray paint is also compatible with cellulose-based paint - and many other types.

Perhaps I have misunderstood you.

Al.

[ColinTheAmpMan1]

I thought that I found somewhere that zinc-plated steel (galvanised steel) needed to "passivate" before painting. This explains why new lamp-posts and such like on roads are left for a year or two before painting. I have seen architectural metalwork (railings, actually) that was galvanised steel and painted before passivation end up with the paint flaking off and looking horrible. It required wire-brushing and repainting at some cost to correct this mistake.
The "passivation" involves the surface building up a layer of oxide, hydroxide and probably carbonates of zinc, to which the subsequent paint coat adheres fine. I think that the passivation process can be sped up by the application of some substances or other, but I can't be sure. I would try to contact a specialist paint company for advice.
Are you sure that the metal is zinc-plated? Just a thought.
Colin.

[Skywave]

Originally Posted by frankmcvey

Hammerite is designed to work without an undercoat.

Not necessarily. Before applying Hammerite to bare zinc, aluminium and galvanised surfaces, Hammerite Special Metals Primer should be applied first. (Copied from the text on the side of a recently-purchased tin of Hammerite 'Direct-to-rust metal paint').

Al.

[paulsherwin]

Al, glad you have no problems using acrylic spray cans - but that doesn't seem to be the common experience, and it's certainly not mine. It does depend on what you're trying to paint though.

The standard problems with domestic aerosols are sagging and orange peeling. Obviously skill levels and technique are important but water based acrylics are just more difficult to use. A recently retired acquaintance used to work as part of a dedicated remedial group at the BMW Mini factory, repairing the frequent ex paintshop problems on new cars. This is a state of the art plant.

[emeritus]

Hammerite certainly does seem to be different from other paint technlogies. Looking for some black paint in the garage yesterday I came across an unopened tin of Hammerite black gloss that I have had for some years, and noticed for the first time that you are instructed to only use a special Hammerite solvent for cleaning brushes. You are specifically instructed not to use white spirit or cellulose thinners.

I used to use Zinc Chromate primer that was said to be suitable for use on zinc plate, but, like traditional lead paints, it is now seems to be unobtainium.

[vidjoman]

Afaik the old Hammerite paint is very different to the current offering. All due to the nasty fumes/solvents etc that are now banned/restricted.

[David G4EBT]

I'm not a fan of Hammerite, but I was in a DIY store this morning, so checked out Hammerite products to see what they say on the can, which is:

RED OXIDE PRIMER
A high performance primer for rusty
or clean iron and steel.
• Special anti-corrosive formulation
• For interior and exterior use
• Provides a smooth protective base
for overcoating with minimal sanding
• Topcoat after 6 hours
• 250ml, 500ml

Note that red oxide primer is for 'ferrous metals', which galvanised steel is not - leastways, the surface coating isn't, being zinc.

It says on the red oxide can that for non-ferrous and galvanised steel their 'special metals primer' should be used.

(I presume that this ambiguous term means 'special primer for metals' rather than 'primer for special metals').

Here's what they say about it:

SPECIAL METALS PRIMER
Specially formulated to promote adhesion on non-ferrous metal surfaces.
• Quick and easy to use
• Only one coat required
• Topcoat can be applied after 1-2 hours
• Colour – Red
• 250ml, 500ml


http://www.hammerite.co.uk/web/pdf/p...guide_2013.pdf

Furthermore, Hammerite also sell 'Direct to Galvanised Metal Paint' which is applied direct to the metal without the need for a primer:

Quote:

'Hammerite Direct to Galvanised Metal Paint is specially formulated for application straight onto non-rusting metal, such as galvanised steel, aluminum, copper and brass, as a primer and topcoat in one. Can be applied direct to galvanised surfaces with no need for a primer'.

Only one coat required.

Unquote.

http://www.hammerite.co.uk/products/...etal_paint.jsp

As to painting galvanised surfaces, I guess that the Galvanizers Association are as good an outfit as any to seek advice from:

http://www.galvanizing.org.uk/learn-...vanized-steel/

I'm not sure that any of this is relevant to the chassis in question - as far as I can tell, there's no indication that it was in fact galvanised. What is in question is why the top coat paint applied to the Hammerite red oxide primer reacted in the way that it did, when Hammerite say that their primer is 'compatible with most paints' without giving any examples of paint with which it is not compatible. Just 'marketing speak' to cover all their bases I guess. Fact is, in the instance, it failed to come up to scratch.

I've long since given up on trying to get a presentable DIY finish with hammered paint on anything that matters, such as a radio cabinet, whether applied by brush or aerosol. Daubed on metal railings yes, and I spray my mower deck with red smooth Hammerite spray when I strip it down in winter, but only because it cost £2.00 a can for four cans at an auto-jumble.

[Nickthedentist]

I did my galvanised garage door with Hammerite SMP before painting with normal gloss. It worked perfectly and has lasted better than the original, factory-applied finish.

I also use 'Acid 8' and Halfords paints, never had a problem, also they are 'just round the corner'. Mind you I have had funny looks lugging around a radio looking for the right match (I had just bought it and was on my way home). After all they are designed to paint mild steel that lives outdoors.