Painting galvanised steel

[Toots]

Slightly off topic but what's the best way to prep galvanised steel for painting?
I have Mordant solution, galvanised primer and coach paint. After a good clean and degrease would I be best using Mordant and the galv primer or is that overkill and will the primer suffice?
Article in question is a lovely shiny new bulkhead for my S3 Land Rover

 

[TLM]

Generally a stable Zinc salt of some suitable acid has to be on the surface for the paint to adhere. Mordant solution creates just that, zinc phosphate is quite stable, I don't know what the small amount of copper actually does. Most paints adhere to that well, depends on what one intends to use if a primer is still needed.

 

[Broch]

I can only tell you what process I have followed that has worked - there may be better ones though.

1) hot soap wash then rinse
2) etch primer, 2 coats - make sure it claims suitability for galvanised steel
3) top coat of quality paint

I use U-Pol Acid #8 as the primer and, typically POR-15 top coat

I've never used a mordant or T-wash

Oh, and on a Series 3

 

[MrEd]

Mordant wash then paint is what I have done on various galvanised Land Rover parts

 

[TLM]

Hmm... looks like "mordant" is the generic name for anything helping in sticking something to something. T-wash seems to be the phosphate solution. Phasphatizing is industrially the the most used surface treatment for Zinc before coating. Other things work but probably not as well.

On galvanized roofing sometimes it is let to age for a year or so and a zinc carbonate layer forms, that works up to a point. The sheeting requires a very thorough pressure wash before coating though.

 

[Toots]

Cheers gents. I've spent the morning giving it a good wash with hot soapy and many scotchbrite pads then a good rinse. Now its in the garage drying. It is indeed t-wash I've got so next dry day it'll get a coat of that then another good rinse and dry. Not sure if I'm brave enough to go straight for paint so I'm thinking a coat of etch primer then deep bronze green goodness. Then the fun of swapping it starts. What could possibly go wrong..............

 

[TLM]

so I'm thinking a coat of etch primer

An etch primer is supposed to do the same as T-wash, redundant I think and possibly problematic.

 

[Broch]

I have a lovely new galvanised front bumper on my SIII; I need it to fade a bit

 

[MrEd]

Deep bronze green is my favourite colour