Primer question

[tyroguru]

Millions upon millions of apologies up front for such a basic question but I want to do the right thing for what's left of my cars thin metal so don't want to make a dumb mistake.

Over the last few months I've come to the conclusion that I'll only be happy if I take the car back to bare metal and go from there. This could be a long process and take the heat off Jason for his long build time so everything has an upside for someone . This will mean getting the car blasted at some time but that's a way off. I'm currently removing underseal and the process does get me down to bare metal at points despite how hard I try not to remove the base primer layer. I figured I'd apply a primer to stop flash rust but I read that a lot of primers are porous - hrrmphh. Can anyone tell me what type of primer I need to apply to bare metal that is going to sit for a year or so? I'm assuming that I don't really need a more expensive 2k epoxy primer for this and that the porosity of primers could actually give me problems after a while on good metal.

Obviously, I'll take any and all input on how to go about this so feel free to chip in with ideas and suggestions!

Thanks!

Jon.

 

[AliK]

U-POL acid etch primer is a known favourite. But for a whole year? Not had any experience with leaving it that long.

Be very careful of spraying 2 pack without the correct ventilation and masks with correct filters. It is toxic to and many have done permanent damage to themselves / their lungs with it.

 

[Turn & Burn]

Ask the blast shop, they’re probably the experts. I did and the blast shop confirmed that yes undercoats can be slightly porous but that’s a real long term thing. Took me 2.5yrs on my shell and by the time I’d finished I still had no rust issues on bare etch primed areas. Loads of bits on the car also had weld thru primer applied on top of the original primer. I would never leave it outside in primer tho.

 

[tyroguru]

Thanks Gents. The car is housed in a garage which is plasterboarded + insulated and also has double glazing so a reasonable place for it to live long term - I've done more work on that garage than I have on the house . I'll read up on the U-POL acid etch.

 

[richiep]

U-POL acid etch primer is a known favourite. But for a whole year? Not had any experience with leaving it that long.

Be very careful of spraying 2 pack without the correct ventilation and masks with correct filters. It is toxic to and many have done permanent damage to themselves / their lungs with it.

Depends on what 2k you are talking about. 2K epoxy primer like the Spraymax 2k primer filler I use DO NOT contain isocyanates. You should still wear a reasonable mask but it does not require the same precautions as the iso 2Ks. Same as the Rustbuster Epoxy 421 - that is iso-free and suitable for DIY use. Doesn’t come in aerosol form though so you need suitable spraying equipment. I use the Spraymax cans as they are useful for section by section painting over the weld-thru Novol bodywork primer Dixie is covered in. Once done though, I may give the whole car a coat of Rustbuster 421 as a final sealer before 2k hi-build coats (again, you can get iso-free versions).

If you are leaving it for extended periods, epoxy - which is hydrophobic - is the only sensible modern solution. Acid etch is basically “old tech” these days. It still has its audience, but is not meant for long term protection.

 

[moggy240]

I would just use a good quality aerosol etch primer for any bare metal and when the car is ready for the paint shop have it blasted and then use 2k epoxy primer. I used the Novol 2k epoxy primer on my car.

 

[AliK]

Another school day!! [emoji106]

 

[tyroguru]

Another school day!! [emoji106]

Indeed Ali! I'd definitely be bottom of the class in this one though .

There is so much information to absorb when you know next to nothing. I love the learning and that's a big part of the car for me but I'm definitely suffering from "paralysis by analysis" at the minute though. Must move faster.

 

[richiep]

I would just use a good quality aerosol etch primer for any bare metal and when the car is ready for the paint shop have it blasted and then use 2k epoxy primer. I used the Novol 2k epoxy primer on my car.

Note that Mike says here etch primer but subsequently blast before applying epoxy. Epoxy primers are not compatible with acid etch primers. Put epoxy over acid etch and it will fail.

 

[tyroguru]

Note that Mike says here etch primer but subsequently blast before applying epoxy. Epoxy primers are not compatible with acid etch primers. Put epoxy over acid etch and it will fail.

Richie, it reads to me like you're saying that epoxy primers will fail even though the acid etch primer has been blasted? If so, what does the acid etch do to the base metal that is so fatal in the process?

 

[AliK]

Indeed Ali! I'd definitely be bottom of the class in this one though .

There is so much information to absorb when you know next to nothing. I love the learning and that's a big part of the car for me but I'm definitely suffering from "paralysis by analysis" at the minute though. Must move faster.

It’s all relative - for every fish there is a bigger one in the ocean


Someone asked me once why I tinker so much with my car and it’s the same as you - the joy of ownership for me is a combination of driving and constantly learning / tinkering. I have always tinkered with cars since being 12 years old and thought I knew a lot - until I bought the Z and realised how little I knew. With the Audis, the computer (VCDS) tells me what’s wrong and I just fix it - often new part replacing old. With the Z you have to actually understand what is happening, go back to first principles and troubleshoot (e.g. tuning the carbs, setting correct timing etc). Frustrating at times but brilliant learning.

Mr Moggy knows his stuff on paints!! I think Richie meant don’t spray epoxy over etch but rather get al the etch off first to avoid the issue he mentioned.

 

[tyroguru]

Mr Moggy knows his stuff on paints!! I think Richie meant don’t spray epoxy over etch but rather get al the etch off first to avoid the issue he mentioned

Thanks Ali. Yeah, I was certain that was what Richie meant but he really does his research on things so I wanted to make sure that there wasn't some other process at work there that he was eluding to. For this phase of the work I'll probably go with a fast etch primer as it's just a "temporary" <cough> metal protector.

 

[moggy240]

I don't like word 'acid etch' as it implies it will stick like shit to blanket. It will not if it has not been prepared correctly and that goes for epoxy primers etc.
What ever product you use, always read the data sheet. I have had to learn the hard way from my own mistakes.

A wire wheel will not rough up metal sufficient for paint to stick to it.

Bare metal needs a suitable grade of abrasive for the paint to stick to it.

Etch primer if being painted over should always be rub down with a suitable grade of abrasive.

Most primers are hydroscopic, epoxy primers less so.

Always get a data sheet for the product you are using. Most of them you can download a PDF from the Internet or your paint supplier can provide.

Any primer for a temporary fix is better than no primer. Just rember that if left for a long time you will have to remove it all and start again.

 

[AliK]

Bare metal needs a suitable grade of abrasive for the paint to stick to it.

.

I learned this through bitter experience!!!!

 

[richiep]

To clarify, what I meant was that epoxy primer is generally not chemically compatible with acid etch primer - you shouldn’t paint epoxy over etch. If you use etch, you should make sure that it has been totally removed, eg blasting, before coating with epoxy.

One of the key selling points of 2k epoxy to the DIY resto market is its longevity of protection compared to the more hydroscopic alternatives. That’s why I’m painting my project bit by bit with the epoxy on the sections that are finished or don’t need work. The red-coloured Novol weld-thru bodywork primer beneath it isn’t meant for long term protection. I’m already having small breakouts of surface rust through that stuff (mostly in areas that need replacing like the previously rotten floor pans). So it’s a case of do bodywork, mechanically clean/prep surface, epoxy.

 

[Rushingphil]

I don't like word 'acid etch' as it implies it will stick like shit to blanket. It will not if it has not been prepared correctly and that goes for epoxy primers etc.
What ever product you use, always read the data sheet. I have had to learn the hard way from my own mistakes.

A wire wheel will not rough up metal sufficient for paint to stick to it.

Bare metal needs a suitable grade of abrasive for the paint to stick to it.

Etch primer if being painted over should always be rub down with a suitable grade of abrasive.

Most primers are hydroscopic, epoxy primers less so.

Always get a data sheet for the product you are using. Most of them you can download a PDF from the Internet or your paint supplier can provide.

Any primer for a temporary fix is better than no primer. Just rember that if left for a long time you will have to remove it all and start again.

Exactly. It's why I'm using the vacuum blaster - to give a rough surface for the paint to adhere to. It also has the added benefit of really getting down into the minute scratches and imperfections that might be harbouring rust.

 

[tyroguru]

What ever product you use, always read the data sheet. I have had to learn the hard way from my own mistakes.

Cheers Mike. I've got some U-POL Acid#8 as Ali suggested so I'll give that a go and see how I get on. The data sheet says to use P180 to abrade bare metal and obviously to degrease before that (POR15 cleaner/degreaser being used there). I'm using an MBX metal blaster to remove underseal/paint and so far I'm pleased with it although I haven't done too much. I'm hoping that I'll be left alone this weekend to have a solid couple of days in the garage to make some progress.

 

[moggy240]

I use a mbx wheel at work, to get the most out if the wire wheel I regularly take it out and flip it over so that it spins the wire wheel in reverse on a 80 grit disc or paper to sharpen it up then take it out flip it over and it will be like new again.
It's a shame they just don't have reverse function like you get on a drill as it would be so much easier.