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Base coat cracking questions

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zeebo76 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeebo76 Quote  Post ReplyReply Direct Link To This Post Topic: Base coat cracking questions
    Posted: Oct/15/2019 at 3:29am
Hello everyone.  I’m getting close to being finished with my very first paint job, done on the 1986 Eagle I’ve been working on for a while now.  It came into the family as an all beige car, and a lot of the plastic trim was chipped and showing black.  Don’t worry, I’ll get to my question soon - for the moment, however, here’s a picture of the eagle I took about an hour ago.


So, as you might imagine, while installing the flares and the plastic runner along the bottom, there was the occasional bit of twisting and tugging done to get some of the screw holes aligned.  A few series of small spiderweb cracks formed (only in the base coat) from these instances on different pieces, and it has me a little worried...  Do these small cracks have a chance of expanding and causing a serious problem as the car is driven?  The clear coat is solid, it’s only the base coat - duplicolor perfect match acrylic lacquer, in ford toreador red metallic.  I can feel over the clear coat and it’s perfectly smooth.

Since the cracks formed only in moments of high stress on the trim pieces (I.e. being bent in ways they wouldn’t ordinarily be bent under normal operating conditions while installed on the car) and never spread more than an inch in any direction, I’m wondering if it would just be a better move for me to tear everything back down and try to fix those spots rather than wait and have to take everything off again further down the road, when the cracks have totally compromised most of the paint.  My main concern is vibration from driving, and body flex from driving down dirt roads, hitting potholes, things that cars go through on a daily basis.

Do any of you have experience with problems like this?

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401MATCOUPE View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 401MATCOUPE Quote  Post ReplyReply Direct Link To This Post Posted: Oct/15/2019 at 5:22am
For parts like those flares and such, my experience has been, I have always added a flex agent to the paint to NOT crack as it moves.  I did all the flares and airdam on a 78 King Cobra and never saw any cracking.  Not sure what kind of base coat you have used.
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zeebo76 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeebo76 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/15/2019 at 12:35pm
Well, for one, this was a rattlecan job.  I don’t have any proper painting equipment, and even if I did, I don’t have the space to use it.  I’m not sure if there are any spray paint cans that have the flex agent already in them, while also having a good color to them, too...  I’m guessing your king cobra’s trim didn’t crack at all, though!
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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Oct/15/2019 at 12:41pm
Any rattle cans for plastic bumpers paint have the flex agent in them. I use these for interior plastic parts also.
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mixed up View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mixed up Quote  Post ReplyReply Direct Link To This Post Posted: Oct/15/2019 at 1:04pm

any paint used on flexible parts need a flex additive or it could be poor prep of surface 

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tyrodtom View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tyrodtom Quote  Post ReplyReply Direct Link To This Post Posted: Oct/15/2019 at 8:45pm
Of any paint out there,   lacquer paint would be my last choice to put over anything flexible.

Way too brittle, flex additive or not.

Once a paint cracks,  it continues flexing in the same area from that point on,  those cracks will eventually come through the clear,  and if you let it go on long enough, will even result in the plastic under it cracking.
I've seen a Vette bumper that broke into 2 pieces,  after what started as a crack in the paint was allowed to go unrepaired for years.   The crack got deeper with time till it went all the way through.

In my experience with flex additive with lacquer paint,  it doesn't make the paint flexible forever,  it just lets it be flexible long enough for you to install the part.  

That's one of the reasons GM,  who used to paint all their cars in acrylic lacquer, switched to acrylic enamel starting in the late 70's.   That's when flexible bumpers started to become common on most cars.   GM got tired of warranty repairs on flexible bumpers.
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zeebo76 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeebo76 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/16/2019 at 1:32am
As much of a bummer as that is to hear, Tom, that’s sort of the answer I was looking for.

It was my fault for not recognizing that plastic parts will have a fair amount of flex to them, especially compared to metal, I ended up choosing the lacquer simply because toreador red was a beautiful color - the paint was super easy to apply, as well.

I take it this will probably last a year or so, if treated well.  I’ll be putting mud flaps on the eagle, so that should help.  This paint job is only intended to hold on until I have the funds to get it in for a few things - completely new full paint job, pinstriping, bodywork (has a few dents), so I’m not TOO sad about hearing that it won’t have the longevity I was aiming for.
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