Clear Coat and Single Stage Mils...how much is too much?

I do about 4 coats and have never seen an issue - did the 3-sand3 on my daily driver truck 15 years ago still looks great- But back to part of the question- and I am curious - does “25” coats of clear look deeper and better than 6 ? I’m planning on doing my wife’s mustang and I have wondered about number of coats. I typically do 4 and maybe 5 if I’m feeling lucky - always looks deep - will more look better ? If so then I’ll do as many as I can ( of course sanding after every 3-4 coats )
 
Chris_Hamilton said:
most every paint manufacture sites no more then 3 coats for proper mil build. the reason is more paint chips easier will not flex as it should leading to checking and cracking paint down the road years later.
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I think he is right about what the manufacturers say, but the manufacturer that you are going to use says different, because the clear is not hard like most, and is also more flexable. People using SPI only have to worry about the thickness of whats under the clear.

edit: Added "what the manufacturers say"
 
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Is the guy totally wrong? No.
Yes, most companies say three coats; you are increasing stone chip potential and losing clarity.
So true today, as I have said many times
The big bucks for the majors are the big chev dealer, not the restoration shop.

The only clear from the old days left over is 2002 from PPG, and this clear makes the guy look like he does not have a clue, but I bet he has never used it before!
Remember the 7800 glamour clear from Dupont, another great product.

All my clears defy what he said, but im making my products for the restoration end of this business since we started in the 90s.
Yes I tell all my insurance shops two coats of my clear are all you need
 
Any of my buddies in production/collision paint work laugh at me at the hours spent on cutting and polishing. Anyone who just does collision work and never ventured into the resto/custom side of things just doesn't understand the process, and that's ok. These guys haven't really heard of poly primers, don't use epoxy primer etc.....

And ill also add, that the guys in the "resto" side of things tend be a bit more sensitive about "their" process. Probably way over think things most times. And the production guys just go along with whatever process is tied to the particular brand that is in their shop at the moment.
 
"Philosophical reply only...I've found through my musings and learnings and failures and wins that there's very little to this trade that is black and white or so absolute, yet so often, things are spoken of in absolutes" -Lizer

I certainly agree! If you want to start some fun just ask a group of professional Corvette painters "should I gelcoat my old Corvette before I paint it?" I have made that mistake a couple of times, ha!
 
To a large extent--success over the desired lifetime of a refinished item with any applied paint coating thickness is often what that substrate is (sheet steel, sheet aluminum or fiberglass) and what environment it will see is, and for how long. Mils of applied refinish coatings leading to long-term adhesion success should be as thin as possible and no more if something like a car is actually desired to be used as a car or is it some kind of expensive play-toy taken out on a trailer to show every-so often. Ask anyone who earns their living in corrosion about that and the science of failures of coatings. Sull coatings are usually preferred to thick beyond whatever case histories support the usage and expectation for life. It is up to the end-users in the trade to figure that out themselves and most like to keep that information for themselves for obvious reasons.

20 or 30 coats of clear on fiberglass won't have much problems with expansion and contraction on a hot day but not so much so on aluminum sheet metal. The paint film does not expand or contract any rate close to what it is adhered to for steel aluminum and consequently has a fair bit of tension developed in the film to stay together. Keep adding layers and a point of diminishing returns begins where what you want to achieve with perceived durability etc. goes the other way. Chipping is result of the developed tension in the paint film with expansion and contraction imbalance and more prevalent the thicker the film. Apply a sudden stone impact and your tensioned paint isn't as ductile in that spot--hence it cracks off. That's what chipping is-- cracking with the crack start and end connecting in a localized area. Thinner the last applied film product is better for actual use being driven around for this reason and that durability. Acid rain or other fall-out--another story for cars being driven in those areas with respect to surface degrading of the coating.

When the USCG ice breaker ships--Polar Seas and Polar Star were in drydock in their 3 or 5 year cycle, the painter doing the bow of the ship was using some kind of catalyzed finish applied with a short nap roller and a wooden stick! Yep, they had done airless, air assisted airless and conventional and found this to be the most durable, lowest cost and fastest method with the greatest adhesion retention in service. He was rolling out just one thin coat only just to get coverage over the primer. Surprisingly, the ship's paint look good coming into the yard from a harsh environment and mission. That painter had been specially requested because he had the right feel to get best results in applied mil thickness in one coat that gave the greatest durability. It was fun to talk to him and gain his insights into doing this and why.
 
Dave C 5 said:
I do about 4 coats and have never seen an issue - did the 3-sand3 on my daily driver truck 15 years ago still looks great- But back to part of the question- and I am curious - does “25” coats of clear look deeper and better than 6 ? I’m planning on doing my wife’s mustang and I have wondered about number of coats. I typically do 4 and maybe 5 if I’m feeling lucky - always looks deep - will more look better ? If so then I’ll do as many as I can ( of course sanding after every 3-4 coats )
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dave, a sanded and buffed 4 coat job and a sanded and buffed 25 coat will both look the same. i personally dont see any difference in the depth. doing a solid color on a car i would always do 3 coats, block and do another 3. it just gets the finish more urethane wave free. there is really no need to do more than that. for my jobs, that was always different. i did it for a reason. i had many layers of artwork and pinstriping to level out so you could not feel any of the stripe edges. i needed a glass smooth finish. i had just mentioned the 25 coat jobs to make a point that i saw no difference in chipping on those than i did a 3 coat job...using universal of course. an extremely hard clear may be a different story.
 
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