Why automotive clearcoat splits

Barry

Barry

Paint Fanatic
Staff member
Somebody sent me this link on another forum and asked what would cause this, hope they don't mind me borrowing their picture but this is as clear as day as to the problem and I believe a good education.

We have to ASSUME everything was activated right and I think that is a fair assumption as underside of a hood, not much work is normally done.

When ever you see these types of splits, it is almost 99.9% of the time, one thing and one thing only! Piling of base without proper flash time.
I have seen this on hoods where the clear will pull away a 1/4 inch from the edge of the hood and the bad thing about this is it always looks like the clear is at fault.

Painting the underside of hood, it is easy to have 3 and 4 coats in some areas with just one coat applied and I have seen and been guilty of it also applying the base all in one application in these types of areas. The base is now contracting and cars i have seen in person, this starts in 3-6 months on the outside, inside with a lot of heat could speed this process up big time, just like baking could.

Thought this might be of interest to you. image.jpg
 
so really what it is doing is shrinking away from a central point??
 
That's crazy I thought it would just die back putting clear over a few coats of unflashed base. Learning something new.
 
I seen something similar with PPG's clears in the 90's that had to do with using their accelerator and cold weather, most of the cars came back with all of the clearcoat shattered.
 
Bob Hollinshead;35636 said:
I seen something similar with PPG's clears in the 90's that had to do with using their accelerator and cold weather, most of the cars came back with all of the clearcoat shattered.
Click to expand...

Bob I used PPG clears for about 4 years in late 90s. I can confirm your findings. Like plate glass windows!
 
What happens here is most basecoats are 12-22% solids and once you start piling on solvents get trapped real easy and the excessive solvents will slow the clear down from curing like it should, as the solvents evaporate over time the base contracts and the clear is very flexible at this point because it is still loaded with the base solvents and moves with the base.
This is only caused by extreme thickness of base, nothing worse then using base as a liquid bump.
A spot repair type clear may take another route and strictly delaminate instead of contracting with the base.
Either one of these scenarios will happen usually in a month to 6 months.
 
RodMan;35639 said:
Bob I used PPG clears for about 4 years in late 90s. I can confirm your findings. Like plate glass windows!
Click to expand...

and the DAU75 was the very worse for shattering.
 
I'm not sure, I don't think it would.
This is basecoat abuse, and not real common for this to happen, so would not really worry about it.
 
Even more reason to not use the minimum recoat time,
Most base mfg's say you can clear in as "LITTLE" as 30 min.
That is a minimum, under ideal conditions, which few are
dealing with. Don't do that.
I always wait an hour minimum..
Rushing is the number 1 reason for problems and yet most
I read about keep talking about using the minimum times.
 
jcclark;35664 said:
Even more reason to not use the minimum recoat time,
Most base mfg's say you can clear in as "LITTLE" as 30 min.
That is a minimum, under ideal conditions, which few are
dealing with. Don't do that.
I always wait an hour minimum..
Rushing is the number 1 reason for problems and yet most
I read about keep talking about using the minimum times.
Click to expand...

I take a beating on the tech line at least once a week for our recommend times.
73% of our business last year was restoration and street rod shops and THERE ARE 2 types of paint jobs.

Normal collision work and custom.

I tell people all the time, if you doing an insurance repair with two coats of clear, no big deal--put both on the same time, wait 5 mins between coats, it does not matter.
Restorations, how many mils do we have with gallons of epoxy, primer and 4-9 coats of a HS clear?
Time is always on your side in this situation.

Now think about this, if I walk into a big production shops and say, let your base set overnight and flash the clear 30 mins between coats, not so sure they would not throw me out the door.
This is big business for the majors and when they walk in and give fast times, it is impressive and that is how you get that type of business.
Also what are the risks? something I read not long ago, 97% of the people that wreck their car, will not have it in 3 years.
Spend $100,000 on a restro job and good chance you will have it a long time.
 
It's true, most don't own it very long afterwards,
I've noticed that on my own.
Sometimes I know I'm going overboard on a car
that it won't matter on but I do this as a hobby and I
do it to please my self. I have to feel good about the results.
My wife is always telling me "no one else can see it"
right before I redo something I'm not happy with.
So I do it for myself, and others may see it and that's what gets me work.
Besides, I've never had a car come back for a redo (so far).
Most of us chase excellence, even though the customer
can't tell the difference.
 
i learned the hard way if it said DAU throw it in the trash . DAU was the beging of the end between me and ppg .
 
Seems like DAU-82 used to work just fine for me, but then again I was not using too much basecoat, and when I did it was Sikkens.
 
i used 5 to 8 gallons a day at one time. dau had the highest failure rate of any clear being used in the late 70's early 80's. there were numerous problems but the worst was die back. forget using it for custom work , more than 2 coats and it was horrible.
 
I'm tempted to argue ancient history, like the difference between the various DAU lines, but what good would that do? Nowadays we have SPI clear, and all is well. :D
 
I did good with DAU82! It was the same basic thing as their DAU Deltron singlestage and the stuff I did with that back in the early 90's also still looks really good today. DAU82 was formulated for use over lacquer also but there was a high amount of failure when stuff was rushed. I was on a Concept 2020 kick for awhile in the mid 90's but it showed long term durability issues and poor UV protection. I friend of mine has a street rod he did early 90's, really nice 38 chev coupe. It was done in Deltron singlestage topcoated with DAU82 and is just stunning to this day, and he drives it all summer. Even if 82 was available today I wouldn't go back-SPI is light years better!
 
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