Apprearance of the top layers isn't really critical. Integrity of the layers are. You do not want any chalked or delaminating layers. Once those are gone, you should be able to paint over the OEM coatings. You definately do not want to remove the e-coat because of safety and quality reasons.

Good painters will etch the paint on the car to promote adhesion. They will remove paint only when absolutely necessary. You get a better job with less work.

See my other posts throughout the site where I discuss this in more detail.

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2010 Toyota matrix

'93 500 SEL
A bad addiction. Takes all of my cash.

'12 Volvo S80 T6
Needed something that wasn't as hard to deal with as my bad addiction

'18 Mazda Miata
No more boring cars for everyday transport!

This is my understanding as well. The factory paint if still intact is the best base for a new finish if applied correctly.

I am curious if anyone had removed the body mouldings as I am considering 'smooting' the body of my latest acquisition, an '83 300SD.
The greatest challenge I believe will be dealing where the removed moulding meets the trim pieces front and rear that are being retained.

If anyone has a link to share that has pictures or other info, that would be greatly appreciated.

Thanks in advance.

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.

Added paint thickness increases chipping and your assuming the original paint still has good properties after 20 years.
Sand also leaves residue and painting systems can fail to bond to them- just like the black factory replacement panel coatings.
I'd honestly carefully strip a car with aircraft stripper, taping off the seams. Clean up the metal with 180 tri-met paper, a good coat of epoxy primer with acid etching properties- staying with one painting sytem.

M

Actually, that is not true unless you have many multiple layers of paint (8+) or one layer way too think.

Chipping is more a factor of improper design of the coating or improper cure of the coating.

Chipping can be magnified by over or under cure of the coating. How so?

Undercure can cause chipping by having crosslinking (The chemical method by which the monomers, oligomers, and polymers chemically combine to form a high performance coating. This is usually an irreversible reaction.) not be complete. One example of this is when you have one form of crosslinking occuring along one axis of the polymer network and not along another. When you stress the resulting polymer network, you have a defect occur along the improperly cured dimension along the polymer matrix. The stress could be thermal (such as hot water sprayed on a very cold body panel), or mechanical such as a rock.

Overcure can cause a reduction in toughness. The coating becomes too hard and will not flex with stress. This lack of flexibility propagates crack formation in the polymer matrix.

In refinish, improper mixing of the 2k systems will cause over or undercure of the coating. Make sure your ratio of paint to hardener is according to the manufacturer's specification.

If you want an example of how a polymer can be tough, look at how toughness in ABS comes from the combination of acrylonitrile, butadiene, and styrene. These monomers have drastically different hardness (measured via glass transition state or Tg), and the mixture of these monomers makes a particularly tough plastic. It can stop bullets.

If you used just the highest Tg monomer (styrene in this case), the bullet would shatter the plastic and go right through. This is one way you can have chipping from improper design of the coating--making the coating too hard.

Now as for an epoxy, there is no substitute for the cationic e-coat that is placed in the factory. Only in very rare circumstances do you want to completely strip the OEM coating of the car. Please see the link I attached earlier in this thread.

Except for the most recent e-coats, e-coat contains anticorrosive pigments containing heavy metals such as lead and cadmium. These are very dangerous materials. You should not strip a car to bare metal unless you know how to do it safely. And it most cases, you will do nothing but create a lot of toxic waste, risk your health, and promote excessive rusting on your car.

Can a car's paint have good properties after 20 years? The answer is yes. I know this as a fact. Also if the top layer is chalked or damaged, that layer can be prepped to have good adhesion for a new layer of paint. There were suggestions made on how to prep in the link. There are others on the site. Please follow them.

Randy Furguson gave a detailed explanation of his process earlier in this link. It is a good one.

I spent years developing the coatings that were applied at the factory. I've worked in auto factories all over the world. Please listen to those with experience and expertise. Stripping a car is a dangerous, usually unnecessary action.

__________________
___________________________________________
2010 Toyota matrix

'93 500 SEL
A bad addiction. Takes all of my cash.

'12 Volvo S80 T6
Needed something that wasn't as hard to deal with as my bad addiction

'18 Mazda Miata
No more boring cars for everyday transport!

Hire a mobile soda blaster service for paint removal if you like your car bare? Soda blasting media residue will act as a rust inhibitor till you're ready for paint... FYI washing with Dawn dish soap & rinse off using clean tap water on smooth sheet metal, then towel dry moisture before new primer, paint or sealer.---