Shrinkage of GF and plastic bumpers ?

[Belgian1979vette]

Currently my car and divers parts are being sprayed. The loose parts are done first.

We noticed that some waves that were not there in the primer seems to appear after the parts have been sprayed in the heated booth.This is especially so for the original type front/rear bumper/ front spoiler parts.

Is this common and if so, what does one do to overcome this.

Imo, one cannot compensate this in advance. I was thinking of lightly sanding the clear coat.

Any input is greatly appreciated.

thx

Yves

 

[MYBAD79]

The 79 had urethane bumpers so I assume when you say "original style" you're talking about new urethane replacement bumpers. Yes, they're wavy and they will change change shape with temperature... IMO it's best to fit them and mount them to the body and then let them sit outside in the sun for a while .... then prime and paint
This is one reason I used fiberglass bumpers.

 

[mrvette]

I have not seen a straight urethane bumper over 5 years old....YET....

:amazed::clobbered:

 

[Belgian1979vette]

The bumpers are worst, but I already expected this to some degree. However it is worse than anticipated.

The fiberglass parts however do have some of it to. In particular i am talking about the 79 rear spoiler. I noticed something here also. Must mention that this is a reproduction fiberglass spoiler and a new one maybe a couple of years old. I had it out in the sun when primed and sanded etc. but it seems to shrink to.

It is making me afraid that I will see this hapening with the body and doors to. However I need to mention that the older T-tops didn't exhibit this kind of behavior.

 

[mrvette]

I can only say this, I HAD a really nice ~25 y/o Urethane paint on my '72, and it finally packed it in, between getting hit...and a damn deer in the headlights...I tried painting it a year ago.....

I know everyone jumped my case over brands, and shit, but really even IF the urethane was of different brands....

anyway, I wish I left it in light gray primer.....not done a damn thing beyond that....

:suicide:

 

[big_G]

All I can think of are 2 things: they (waves and/or ripples) were there and were hard to see in primer, or you have body filler or high-build primer shrinkage. Gonna be hard to block them out of the clear...not to mention risky.

 

[Belgian1979vette]

All I can think of are 2 things: they (waves and/or ripples) were there and were hard to see in primer, or you have body filler or high-build primer shrinkage. Gonna be hard to block them out of the clear...not to mention risky.

That is a possiblilty, but i had lots of time in between fillers and shooting primer. I also had it sitting in the sun on hot days more than just a couple of times.
:waxer:

I know it's risky in trying to block the clear. Already discussed it and we are not going to do it. Next step is putting the rest of the parts in the paint booth before doing any painting on them.

 

[Belgian1979vette]

Ok, the painter had some unfinished parts put in the heated booth for some time and apparently some small sand scratches and other things started to surface on some of the parts. It's for sure shrinkage is involved.

We are going to put everything in the booth before proceeding and then finish with a high gloss layer before final blocking it.