Rust patch repair - how prime and paint!

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PostPosted: Sun Feb 28, 2021 9:51 am
I am restoring a 1985 Jaguar XJ-S; which I've bought the express purpose of learning new skills.

The stainless window trim is attached to the body with self tapping screws. Over time water has ingress and the paint bubbled and rusted.

I've sanded back the paint with 80 grit and removed as much of rust as possible. I've the applied a rust converter, which I've left and the sanded that back again. Filled any pitting with filler and sand that back with 80 then 120.

As much as possible I've tried to contain the repair to the localised area.

My question now is how do I go on to prime and paint? I've been reading as much as I can as well as watching as many videos on the matter - but there is a lot to take in.

Here is a photo of one of the patches I've done so far.

Image


I'd be grateful for any advice how I can go from this to primed, painted & clear coated. I've got a compressor and (will get) spray guns - and I prefer to use these where possible - not necessarily because its the best tool for the job but because I want to build up experience using it before I come to larger and more visible panels.

Any information, or links to guides, tutorials or videos is great appreciated. Thanks.



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PostPosted: Sun Feb 28, 2021 9:59 am
Oh, that light blue patch in the low left is not a different paint tone, it's blue masking tape!



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PostPosted: Sun Feb 28, 2021 12:01 pm
it kinda depends on how much you have to do. but i would spray that area with some epoxy a couple wet coats, if that's the only spot. you can block the epoxy with 180 until flat then shoot another coat of epoxy finish sand that and apply your color you could also use the epoxy as a sealer if you wanted. it greatly depends on the extent of your repairs. you may want to invest in some hi build primer if you have much more work. for that one spot the epoxy will do everything you need it to do and only haveing to buy one product.
Jay D.
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PostPosted: Sun Feb 28, 2021 1:37 pm
Thanks for the reply.

Out of interest, why epoxy primer rather than other types?

And secondly, the bit I am most anxious about is how to tie the new paint into existing.

I am guessing I should feather our the existing patch area by about an inch, when I apply the primer and base, won't some cover the unsanded original paint? Won't that stick poorly?

...if I were to guess, I suspect I should be finely sanding the top coat but not cutting through it. That way any paint that lands there will stick. And then the new top coat can be applied over it.

Hopefully these drawings make sense

How it is now:

Image


How is THINK it should be, but I am really not sure.

Image



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PostPosted: Sun Feb 28, 2021 2:22 pm
Hi Dobson,

Beginner Home hobbyist here, I think I might be able to advise for this situation. Please do not take this the wrong way, but your drawings are over thinking it as to the layering of things, the thickness of all items is such that it will still be flat when your done. By the way if this is the only repair, you can purchase 2K paint products in a rattle can for this project.

This work would be like a dent repair. The first is to sand a larger area for the primer to adhere to, which will also allow you to blend the work into the finished product. The reason for the epoxy primer is so it will seal the bare metal and give a good solid base for the rest of the repair. You need to get the base fixed first before the primer, in this case use body filler to fill the hole depending on size if you do not have a welder. Then sand with 180 grit autobody paper for smoothness of the filler or grind smooth the weld then filler. Next epoxy primer a masked area 2x the size of the bare area. Then it's get is smooth as you can with a guide coat and sanding finer grits. Then another coat of Primer and then colour in the allotted time for the primer to top coat without sanding. Then the clear coat.

Again, Beginner hobbyist here. This is the way I would approach this project if this is the limited damage you have. If this is the start of more work that you have, then I would go with mix as you go auto paints in the quart or gallon if it's a bigger project and then you can control the application vs the rattle cans and the expiration of the paint after activating it.

Good luck and keep us posted.

TX Mr fixit_PDX
Chris :)



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PostPosted: Sun Feb 28, 2021 3:51 pm
Thanks for a great response, and I am think I am definitely overthinking it; it's hard to know what is and isn't important when you're starting out - so I end up assuming it's all important.

Yes I did exaggerate the size of this simple to show the layers, I know it won't be like that in reality. :)

you can purchase 2K paint products in a rattle can for this project.


There are quite a few things to repair, and whilst a rattle can is probably the most time and cost effective way of doing this - I really want to start building up some experience using the spray gun for some of the more complicated tasks down the line.

in this case use body filler to fill the hole depending on size if you do not have a welder


I have a welder and can weld but I think it's unnecessary for this job. The rust is "only" pitting, the hole you can see is where the self tapping screw goes through. The white stuff is my first coat of filler.

Next epoxy primer a masked area 2x the size of the bare area


Ah this is what I was most keen to learn about. And would you sand this larger masked off area? If so up to what grit? If I don't stand it then how does the new paint key onto that smooth(ish) surface?

Thanks!



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PostPosted: Sun Feb 28, 2021 4:57 pm
(Next epoxy primer a masked area 2x the size of the bare area) i wouldn't do this. feather out the existing color coat with a D/A or sanding block ,pad. you going to have to sand out from the damaged area at least 12" or so i would sand the hole panel it sounds like its going to need it. ( i can't see the area around the repair). then spray the epoxy on the repair area letting it go onto the sanded color coat if it has to. masking is going to create a line that's has to be sanded out to a smooth finish ( not as easy as it sounds ) just let the epoxy fade out being sure it goes over a SANDED AREA.
Jay D.
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PostPosted: Mon Mar 01, 2021 9:12 am
Ok, nearly feel like I've got all the info I need.

What grit should I use to sand the rest of the panel, presumable something high enough to not cut into the existing base coat? 600?

I don't yet have an air DA sander, but I do have an a good quality electric Random Orbital sander, is that any good in these applications?

And finally, let's say I do clear coat a large area but not the whole panel. On the circumference of the new clear coat there will be some amount of sanded old clear coat which didn't get a coating that has been sanded, will scratches from that sanding just buff out?

The panel is the scuttle below the front wind screen which ties into the roof panel. So I really don't want to clear coat the whole lot if it can bee helped - so. there must be a transition somewhere.



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PostPosted: Fri Mar 05, 2021 2:09 pm
Bump.

Hoping to attack this project tomorrow and I'd feel much more confident with knowing the answer to those outstanding questions.

Cheers

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PostPosted: Sat Mar 06, 2021 5:39 am
dobson156 wrote:What grit should I use to sand the rest of the panel, presumable something high enough to not cut into the existing base coat? 600?


For the areas that will just be recleared, P1200-P1500 wet.

For areas that will have basecoat, P600 wet for solid colours, P800 wet for metallics/pearls.

For areas that will be primed, sort of depends on the primer. Epoxy that will be bodyworked and recoated with a high build, P180, even P150. For areas where the primer will just be sanded and then top coated then I like to go up to about P400, so if it shrinks a bit, the sanding scratches won't show through. In your case, probably P400 will be fine; epoxy primer sticks to almost anything.

dobson156 wrote:I don't yet have an air DA sander, but I do have an a good quality electric Random Orbital sander, is that any good in these applications?


Probably, once you have some experience under your belt and provided it's 150mm or bigger. The 125mm ones just tend to dig in. For now, using blocks and hand sanding will give you more control and teach you what you need to achieve with the machine.

dobson156 wrote:And finally, let's say I do clear coat a large area but not the whole panel. On the circumference of the new clear coat there will be some amount of sanded old clear coat which didn't get a coating that has been sanded, will scratches from that sanding just buff out?


Clearcoat blends are the province of highly experienced painters only. While technically not difficult, achieving a result that can't be seen needs much practice and even all the very experienced amateurs here will only clear the whole panel.
Chris
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