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64simon

New Member
I have a very shiny newly galvanised roofrack for my Disco. I want to spray it black but dont know the best way to do it.

I thought I would sand the surface, wipe with thinners, prime with etching primer then top coat with satin black. Am I on the right lines?

Thanks for your help.

Simon
 
Dunno the right answer, but I did try the same a few years ago on my old Lime rover. I used hammeright galvenised primed and a couple of top coats.. It didn't last long at all.. Not good..
 
Either wait until the shine goes , or hamerite or similar , OR proper job is to prime with PLUMBATE PRIMER , good household paint shop will have it . Worked with a sign writer years age and some of the sign I painted like this are still looking good .
 
hi simon, what you need is something called mordent t wash.it,s like an acid that you brush on, it turns the galvo black then you wash it down with cold water.it takes the shine off which is what needed.Etch prime and topcoat when dry.
Hope this helps,regards Mark.
 
key it up , then etch prime it, then prime it, topcoat... or use wurth ruststop primer , key it up topcoat...
 
t wash or mordant solution zinc phosphate primer then undercoat and top coat.Or dulux have a product called metalshield use the qd primer then top coat not cheap but less time.There is also a zinseer product bulleye 1 2 3 wash down with meths then 123 and top coat hope this helps.
 
When I bought my new chassis, Richards Chassis said to use T-wash/mordent solution on new galvanising then etch prime then your preferred topcoat.

New galv contains a greasy element that is not removed by degreaser, over the course of a few years the elements will remove it and you can etch prime straight on to it. I have slapped etch primer onto some old galv followed by chassis black and that held up ok, however the same didn't work with new galv.

Harry
 
Leave the chassis for a year then prime and paint as normal.
Local authorities have done this with galvanised lampposts for years.
 
Thanks everyone your advice has been very helpful.

I have bought the mordant solution and treated the roof rack. It has gone black and looks good to prime.

I now have a second question.
I think the mordant is copper sulphate solution (I used to teach science). The colour change is a displacement reaction in which the zinc displaces the copper as follows:-

copper sulphate + zinc → zinc sulphate + copper

I am sure this is what is happening but have no idea why it is necessary to get good adhesion.

I don't need to know but am such a saddo that if there are any chemists out there I would be interested to find out.

Many thanks
 
There is one possible use of my ramblings. I spent £17 on 2.5 litres of mordant solution. If i am right you can buy copper sulphate crystals on line and make your own for a fraction of the cost.
 
64simon said:
There is one possible use of my ramblings. I spent £17 on 2.5 litres of mordant solution. If i am right you can buy copper sulphate crystals on line and make your own for a fraction of the cost.
Click to expand...

I have heard the same thing but never looked into it. I only used about 1/2 a litre to do a 90 chassis, kept another half litre for the future and flogged the rest for a tenner... ;)
 
Jongould said:
Their latest paint does go straight on, its formulated as a 1 coat paint now. I don't know how good it is as far as durability but its definitely 1 coat paint
Click to expand...
right im right and your right talking to akzo nobel rep and his bosses today hammerite does not go straight on to galv, but hammerite has launched a new product called straight to galv. Which is what your talking about but they are 2 seperate products:)
 
Hammerite strait to galve, it looks great at first after around 6 month it starts peeling off and is a right bastard to sort,mordent, it goes grey black then prime and paint,4 years later no problems.
 
To conclude.

I tidied the galv with a file.

Treated with mordant.

Sprayed with etching primer.

Sprayed with satin black.

This was 3 months ago, it hasn't peeled off yet (and shows no sign of doing) and still looks good.

A success!
 
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