How to: Prep for paint, from bare metal or respray

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PostPosted: Wed Aug 24, 2011 11:17 pm
Correct me if I'm wrong,,,but I don't think waterborne cleaners are designed for bare metal.......
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PostPosted: Thu Aug 25, 2011 8:09 am
OldDupontGuy wrote:Correct me if I'm wrong,,,but I don't think waterborne cleaners are designed for bare metal.......

That is true of the pro spray waterborne cleaner and possibly Nexa
http://www.prosprayfinishes.com/images/ ... 0_0611.pdf
http://www.fycracing.com/graphite03/FSM ... RM2842.pdf



But almost all the others can be used on bare metal and the owner of SPI who is a paint tech question wizard has this to say about it

Barryk
09-03-2010, 08:11 AM
A subject dear to my heart for sure.
Each solvent has their own strengths and I just can't put in writing how good the waterborne is for cleaning bare metal, aluminum, chrome, stainless.

These types of substrates require a different type of cleaning and to prove it to yourself, next time you have sandblasted bare metal, with clean towels clean a three foot spot with the solventbourne, then with clean towels go over the same spot with the waterborne, the clean towels will look like you did not even clean in the first step, so important to adhesion.

http://www.spiuserforum.com/archive/index.php/t-68.html.
http://www.southernpolyurethanes.com/te ... 202006.pdf
http://pc.dupont.com/dpc/en/US/html/vis ... _TDS_E.pdf
http://www.bodyshopbusiness.com/Article ... eaner.aspx
http://www.qhfonline.com/product/QSOLV% ... 0V0609.pdf
http://pc.dupont.com/dpc/en/US/html/vis ... _3901S.pdf
http://www.sikkenscr.com/sikkenscr/uk/P ... /M200.aspx
http://www.bapspaint.com/docs/psheets/P ... leaner.pdf

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PostPosted: Thu Aug 25, 2011 9:33 am
I stand corrected,,,Years ago when they first came out, I "think" they said that it was not recommended for bare metal.
Thanks!
Waterborne cleaner is some good stuff!
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PostPosted: Thu Aug 25, 2011 9:57 am
I have not had a chance to use a good quality waterborne cleaner. I have used some cheap Rustolem waterborne cleaner, it was OK, but flashes VERY slow.... I'm hoping the good quality cleaners flash off a lot faster. :?



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PostPosted: Thu Aug 25, 2011 10:45 am
From what I gather, the cleaner makes the contaminates float, and then can be wiped off. So the cleaner should not dry too quickly, and I think SPI has the right window on drying. I was using Dupont 3901s before, but SPI blows it away, and only cost half as much.


OldDupontGuy wrote:I stand corrected,,,Years ago when they first came out, I "think" they said that it was not recommended for bare metal.
Thanks!
Waterborne cleaner is some good stuff!

After all the useful info I have gotten from your comments, its good to be able to make a small payback.

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PostPosted: Thu Aug 25, 2011 10:11 pm
Thanks Rock,,

Just for the record,, All of your cleaners make the contaminates float.
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PostPosted: Fri Aug 26, 2011 6:14 am
I mean after wiping it with a dry towel, there was still cleaner left behind that needed to flash. I could blow it off with air, but that kinda defeats the purpose. ;) I'll have to try some of the SPI waterborne next time I need to buy supplies.



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PostPosted: Sat Sep 17, 2011 9:06 pm
I'm super new to auto body. My motivations are a little different. I race in Spec Miata, and very often I need to paint my car. The paint does not need to be perfect, but being a perfectionist makes me want to learn the trade to perfection, so that I could restore my beloved cars.

Over the last few months I build my own race car (suspension, interior, engine, trans, setup, etc) without knowing anything before. The last thing I'm lacking is auto body. Internet search let me here onto this forum and this thread. Even though the message in the thread is great, it seems confusing to me. Excuse my lack of knowledge on the subject, but that's how I understood your preparation for paint:

Given:
We want to prepare an existing METAL piece.
The given metal piece has existing paint on it.
The job has to be done from scratch (bare metal, completely refinished).

Steps:
0. Remove trims and accessories (I reversed your steps as this will allow me to wash the car better)
1. Wash the metal part with soapy water. (warm water, high quality non-wax auto shampoo)

now, this is where you lose me:

2. Wipe the car or panel down with Wax and Grease remover ( I believe this step is in the wrong order)
a. Let the solvents flash (dry) for at least 20-30 minutes before priming or painting any panel

OK, when does the sanding happen? According to you after wipeing the panel you give yourself 20-30 minutes for paint? Am I missing something here?

3. Apply organic solvent (I believe this step is in the wrong order)
4. Sand the panel. (here you wrote this: "If prepping bare metal, P80 grit paper on a DA sander ....", does this mean you are working with a painted panel that you want to strip down to bare metal. I'm not sure I understand the word selection: "If prepping bare metal". Did you mean if prepping a painted panel and removing the paint to bare metal?
5. Blow off the panel and wipe it down (as outlined above) before priming. (I'm assuming this is step 2 and 3 from above)
6. Apply 2 coats of epoxy primer.
7. Apply 2-3 coats of high build primer ( I have no idea why a total of 5 coats, but I'm new so I believe this is valid).
8. Seal the primer, or final sand high build primer before color.
9. Apply your primer or paint. (you lose me here as well, what do you mean by apply your primer? We already applied 5 coats of primer).


Please help me order the steps as I feel step 2 and 3 are out of order. Also please explain why do I need to wash anything before sanding?

Sorry for being picky, but I will not know otherwise.

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PostPosted: Mon Sep 19, 2011 1:13 pm
Before you sand anything you need to make sure it's clean. That means both washing with soap & water, and using a good W&G remover. Once it's clean then you can sand it. Doesn't matter if it's a new replacement part you just bought or an existing finish that needs to be stripped down to bare metal, you should clean it before you sand.

Once you are done sanding, blow the panel off with compressed air, wipe it again with W&G remover (make SURE you follow the tech sheet for your W&G remover - this is a step that can cause future adhesion failure if not done correctly). Before painting it's also a good idea to use a tack cloth to get any remaining specs of dust/dirt off the panel(s) as well.

You can shoot a direct-to-metal primer (etching primer) or epoxy primer on bare metal. The next step of shooting high-build primer is optional and depends on what your goal/preference is. If the etch primer or epoxy you are using can be sanded, and the panels are in very good shape, then you can go directly to block sand (or even skip block sanding if the panels don't need any correction), and then color.

High build primer is used when you plan on iteratively using a guide-coat then blocking the primer down flat (over and over again until the panels are "pefect") -- then you go to color. 90% of high-build primer you spray on ends up as dust on your garage floor, after you are done blocking the panels flat.

Sealer is also optional. Personally, I try to keep the number of layers of "stuff" to a minimum. The more times I pick up a spray gun, the more solvents are being hammered into the materials that are already on the car, and the more chances for introducing a problem. If I can get away with it, I shoot epoxy primer, do my bodywork, shoot a couple more coats of epoxy primer, block that and then color.



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PostPosted: Mon Sep 19, 2011 1:49 pm
If I can get away with it, I shoot epoxy primer, do my bodywork, shoot a couple more coats of epoxy primer, block that and then color.


Good point. The '63 fender I'm working on had some repaints over the original finish, but the original primer, which seemed very thin, was stuck like glue to the fender. The solvents would've all evaporated between the paint jobs, so the subsequent repaints adhered very well.
The build date of the car is September 20, 1962, so that's 49 years the old technology primer didn't fail. Imagine how long today's primers will last, if properly applied.
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