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[email protected] edhuntress2@gmail.com is offline
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Default Modern car paint and rust

On Wednesday, February 15, 2017 at 5:19:11 PM UTC-5, amdx wrote:
On 2/12/2017 4:03 PM, wrote:
On Sunday, February 12, 2017 at 3:01:15 PM UTC-5, Clare wrote:
On Sun, 12 Feb 2017 10:43:40 -0800 (PST), Christopher Tidy
wrote:

Hi folks,

Quick question. Many cars from the 1980s used to rust badly. Sometime in the 1990s, this changed - and quite suddenly. Does anyone know what specific changes were made to the paint composition and surface treatment? I can only find vague allusions in most articles.

Thanks,

Chris
Big thing was change to the surface preparation of the steel to
either electrostatic wet application or full body dip of a high
quality etching primer which I believe contains Zinc.
This was combined with the use of high strength steels and
"galvanized" steel in rust prone areas.


Right. It's better coatings, better primers and protection, and better application. Read, water-based coatings that often are based on urethanes; phosphate and weldable, etching primers; galvanizing in rust-prone areas; and electrophoresis and electrostatic application. The first water-based coatings -- used into the '80s by some manufacturers -- had poor adhesion and didn't weather well. They're MUCH better now.

All of this became more necessary as body panels got thinner, with the use of AHSS (advanced high-strength steels; a continuing evolution of the HSLA [high-strength, low-alloy] steels that were first used in the '70s). Rust is potentially a bigger problem than ever because the steel is thinner.


Why the change to base plus clear coat?
I took an auto body class in high school, we had lacquer and enamel,
44 years ago.
The hood on my sons Toyota had faded and was blotchy. So I went to
the paint store to buy paint. I thought I wanted lacquer, I was quickly
educated that I wanted a base and a clear coat. It turned out good
especially for an outdoor job. We did end up with a small hazy area,
when we started the motor to move it in the garage, before the dew came.
Just one area on the right side near the windshield. I suspect
it would buff out, but he took the car back to college, so haven't
tried. Mikek


Clear coats retain their gloss much longer than standard base coats -- up to eight years for some current ones -- and they contain IR blockers that extend the color life of base coats. They've been standard for years.

That is, for the common "three-wet" (primer, base, clear coat) systems used by most OEMs. As I mentioned earlier, Ford, among others, has gone to a "two-wet" system for commercial vehicles and probably will go that way for cars. The current two-wet system used by Ford supposedly maintains gloss for eight years without a clear coat, but it only works in light colors for now..

These are chemically so far removed from our experience with lacquers and enamels that it takes an expert to explain them accurately.

--
Ed Huntress