9 replies to this topic

[Brams96]

I've read through the 21 Page paint guide but still had a question.

What order is the best to prep a panel from when it's just been welded on (ie bare metal)?

Is it Rust Inhibitor, Acid Etch, Prime, Seam Seal, Colour Paint, Lacquer?? Or is there a better way?

Cheers

[tiger99]

From bare shiny metal, the best basis is to grit blast and then use the best zinc based primer that you can find, as the zinc is ineffective on top of anything else. Follow that by good tough primer, such as epoxy, then seam seal, high build and finish. However, that may be impracticable, so second best is etch primer followed by epoxy, then as above. Underneath, stonechip will be usual in place of high build.

The type of epoxy which is reinforced by tiny flakes of glass or mica may be even better, but it may increase your usage of high build, and more rubbing down.

If there is the slightest hint of surface rust, use Jenolite before you start. Some people use Kurust but I have doubts about being able to put a general coat of etch over a surface which has patches of Kurust. Mechanical rust removal is best.

Ideally you would galvanise, zinc plasma spray the seams, then use a primer suitable for zinc, and high build plus topcoat of your choice, but successfully galvanising a Mini shell is all but impossible. (Actually, zinc plasma spraying is possible, but still needs grit blasting, you could consider it for seams and notorious places for rusting only, as it is a manual process and covering the entire shell would be very expensive).

You could always get it E-coated, then I think it is just seam seal, high build/stone chip and finish. Balance the cost against the cost of doing it all again in 10 years or less, and you may find it attractive. The problem is that it does save money long term, but you need a lot of cash up front, and right now, thanks to the greedy idiot bankers, few of us are exactly rich.

Anything we actually do is a compromise, and others will likely give their individual interpretations of the best possible compromise. It does not mean that anyone is wrong, just that none of us can achieve the ideal, a paint finish that will last for a lifetime, with the materials available, so some past experience, personal opinion, a bit of chemistry, and various other factors will guide everyone's individual opinion. If everyone paints their car today, using their favourite process, and we all come back in 20 years and compare notes, then, and only then, will we know who is correct.

So I am always interested in hearing opinions that differ from mine. I am particularly interested in knowing what particular brand of the various materials that people use, and why.

By the way, after painting, lots and lots of Waxoyl is something that probably most of us would agree on. And, top it up regularly, in sills, door bottoms, top of the scuttle closers, inside of outer ends of bulkhead crossmember, etc. Someone did a writeup on where to put it a couple of months back.

[Brams96]

Tiger99 - Thanks for the reply, any advice is much appreciated. After reading through lots of peoples projects, everyone seemd to do things their own way. So your advice is to:

Media blast
Zinc prime
Epoxy primer
Seam seal
High Build Primer
Colour finish.

My problem is I will be doing all the welding & paintwork myself in my garage, with no compressor (at the mo), cant afford to have the whole shell media blasted but still need to do a decent job so I don't have to redo rust patches again in a couple of years.
I was going to do things in this order:

Weld repairs
Etch primer/Zinc rich primer
Seam seal
Prime
Colour finish

If I use Rustoleum Combi-color or High-hat as a final coat do you think this would be the right order? The Rustoleum is a direct to metal/rust paint with inhibitors so putting it over zinc rich paint might give it more protection.

I also wondered about the inside of panels when, for example a sill, welding it on. Do I strip off all the dull black paint (repro panels) zinc prime to protect, then remove the paint in the area I'm welding, weld it on & follow on from seam sealing. I can't get my head round protecting the inside of panels when welding (obviously apart from filling things full of waxoyl afterwards)

Edited by Brams96, 31 March 2012 - 01:22 PM.

[tiger99]

Well, not exactly. Media blast is not necessarily the same as grit blast, and you need to get the surface really rough for zinc based primer. But as you are not blasting at all, same as most people, you will be reliant on etch primer.

There is no point whatsoever in using zinc primer on top of etch. It requires direct metallic contact to work. You would be better with epoxy primer on top of etch.

For seams which will be welded, use weld-through primer, which may well be zinc based (its lack of adhesion will not matter here), and mask them before spaying the etch.

Don't put any sort of rust inhibitor over zinc, which in any case you can't use on top of etch. Don't put the rust inhibitor over etch either, if it is made for bare metal, that is where it must go.

Paint the insides as best you can before welding, there is no way of achieving perfection.

Depending where you get your panels from, you should either remove all the primer, because it is poor quality, or leave it on except where you will be welding, because it is E-coat. Heritage are E-coat, others vary.

[Brams96]

Ok, I think I'll invest in some more Zinc primer & then use epoxy primer, high build primer & colour coat. Cheers

[sonikk4]

With the fact you have no compressor then maybe an electric DA sander may be of use to you. Use this to go over all of your panel work that needs painting and also at this stage you will need to fill any dents, distortion etc. The filler needs to be applied to bare metal for it to grip correctly. Once you are happy the shell is dent free etc then use a good quality etch primer (UPOL) on the bare metal and go from there.

Any surface rust that may have appeared can be sanded back providing no pitting has occured, if that is the case and the fact you cannot media / grit blast then you may have to replace those affected sections. No point bodging at this point.

[Brams96]

Cheers Sonik, I'm going to be cutting out & replacing any bad metal or wire brushing & Kurust'ing any other saveable parts, I was just unsure of the correct order/process in which to paint the new metal & areas where I'd welded. Some people seem to weld then etch prime and use a skim of filler after that, then they high build & colour coat. Whereas some people do it differently. I just would like to get it right in my head now so I dont cause more problems in the future.
So your saying I should weld the panel in then filler directly over the cleaned up weld? Then go with etch primer & so on?

Edited by Brams96, 01 April 2012 - 11:30 PM.

[Brams96]

Sorry to drag this up again but I had another question, this time about weld through primer.

Has anyone used the FROST Weld-thru Zinc Rich Primer & how does it compare to using say U-Pol #2 primer? It's just it's half the price of U-pol so if it does exactly the same thing Iit make sence to get it instead.
There is U-pol Powercan weld through primer which is cheaper then the Weld #2, is that also good stuff?
And lastly I came across this at Decorating Direct which is a Zinc rich primer (90% zinc) & says it can be used for spot welding etc & is only £5.35 a can.

What do you think?

[sonikk4]

I only use the Upol weldable Zinc primer (personal choice). Filler must go onto bare metal, also its worth keying it as well to get maximum adhesion. The etch will not work on the filler so use it on bare metal only. Then go from there.

[Brams96]

Cheers sonik, gotcha. I can get etch & normal primer cheap through my wifes work so might see if they can get me some decent weld through primer too. Cheers.