What makes the paint crack?
Safety Car
Joined: Jul 2002
Posts: 4,269
Likes: 3
From: St. Charles IL
Cruise-In 5-6-7-8-9-11-12 Veteran
A CI-6 Car Show Winner
Re: What makes the paint crack? (Paul G)
Expansion and contraction of the fiberglass is greater then the film of paint. The only way you can really prevent it is to never let the temperature of the car swing more then a few degrees, and of course we know that is not practical. Maybe some of the newer paints are less subject to this then the original paint, hopefully some paint experts might reply here.
Team Owner
Joined: Sep 2001
Posts: 30,958
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From: Middletown Connecticut
Cruise-In IV Veteran
Re: What makes the paint crack? (Big Fish)
body flex is one of the major causes of cracks. normally its not the paint that cracks (unless its laquer).
I'll start with a laquer finish. As some of you know, Laquer based paints never fully dry, it constantly shrinks over time. It will keep shrinking to a point where there isnt enough to keep it on the body and one good jolt will send it cracking.
Now the question about newer paints... I recently sprayed my car in Dupont Chromabase which is a Urethane based system. My car was flawless untill I brought it to the track and severely flexed the body and I have a nice hair line crack on the rear quarter. Nothin anyone can really do about it
I'll start with a laquer finish. As some of you know, Laquer based paints never fully dry, it constantly shrinks over time. It will keep shrinking to a point where there isnt enough to keep it on the body and one good jolt will send it cracking.
Now the question about newer paints... I recently sprayed my car in Dupont Chromabase which is a Urethane based system. My car was flawless untill I brought it to the track and severely flexed the body and I have a nice hair line crack on the rear quarter. Nothin anyone can really do about it
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
Re: What makes the paint crack? (Paul G)
Typically cracking on a fiberglass body is caused by flexing. The thickness of the paint can aggrate the situation. But there are other causes, specifically damage caused by induced stress. this can usually be found at the rear corners of the hood. This area takes the force of closing the hood and if done improperly can cause stress cracks due to flexing. I usually close my hood by laying it down and gently pressing each corner. The other area where cracks can occur are on the top of the front fenders. This area is exposed on the underside to stones and rocks thrown up by the tires. These usually create stars in the paint. The fix for this is to get some thick indoor/outdoor mat at least 1/4 inch thick and cut out a piece the size of the unprotected area under the fender. Then take this piece and bond it under the fender with Liquid Nails or some other strong adhesive. Top the whole thing off with some black undercoating and you'll never know it's there. This mat will cushion anything thrown up by the tires and prevent the stars on the top of the fenders. I did this to my 74 almost 10 years ago and haven't had a crack on the top fenders yet.
[Modified by vettfixr, 8:55 AM 12/2/2003]
[Modified by vettfixr, 8:55 AM 12/2/2003]
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
Re: What makes the paint crack? (comp)
bet that really lowered road noise to , could you tell a difference after you did
it????
it????
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Pro
Joined: Nov 2003
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From: Camden AR
Re: What makes the paint crack? (vettfixr)
good idea bout the matting, I'll give that a try
my car has original paint (78) and another area I notice problems with is by the door handles...probably from 25 years of people putting their thumbs there (mild flexing) to depress the handle...
my car has original paint (78) and another area I notice problems with is by the door handles...probably from 25 years of people putting their thumbs there (mild flexing) to depress the handle...
