Help Needed ! Mold lines visible thro paint


Hiroboy
07-18-2003, 03:38 PM
http://www.spc.org.uk/misc/mold-lines001.jpg
http://www.spc.org.uk/misc/mold-lines002.jpg

Nissan 350Z in Silverstone/Gun Metal WV2

These were the steps taken as usual
1. Sanded all mold lines out
2. I rubbed down the body with 2000 grit wet and dry,
3. Washed in soapy water,
4. Let to dry
5. Primered left to dry. No sign of mold lines
6. Airbrushed Halfords paint onto body, still no sign of mold lines
7. Clear coated with Halfords Lacquer
Suddenly the mold lines appear !!!!!

Anyone know what causes this to happen
and what I can do to correct it ?

Thanks

bah humbug
07-18-2003, 03:39 PM
I can't help you there and I don't want to make a wrong guess.

IT's weird tho. Sorry to hear that and good luck.

pcmodeler
07-18-2003, 03:43 PM
Sounds like at some point that the paint went on too thick. I usually wet sand with a high grit paper after the primer and after the next to last coat of color.

Hiroboy
07-18-2003, 03:54 PM
Originally posted by pcmodeler
Sounds like at some point that the paint went on too thick. I usually wet sand with a high grit paper after the primer and after the next to last coat of color.
No the paint is airbrushed on therefore loads of thin coats far from thick compared to a rattle can.

It's in the Dot 4 now. But don't want it to happen next time, you can even feel the mold lines thro the clear, when it was dry, Very Weird:confused:

Jay!
07-18-2003, 04:26 PM
Originally posted by Hiroboy
you can even feel the mold lines thro the clear, when it was dry, Very Weird:confused: Feel them raised or depressed?

psycho
07-18-2003, 05:02 PM
Try using a white primer coat. This might make the problem areas appear more apparent.

HTH

Allen

Hiroboy
07-18-2003, 05:17 PM
Originally posted by jay@af
Feel them raised or depressed?
Not easy to tell could be depressed.
Grey kits are a bitch to see when mold line are gone till priming
The primer was white.

Jay!
07-18-2003, 05:36 PM
Originally posted by Hiroboy
Grey kits are a bitch to see when mold line are gone till primingAgreed. Especially flaky/sparkly silver.

Sorry, but I can't explain it...

Maybe try a line of a thicker primer (thinking mr. surfacer 500 or a thin putty) over the modl lines and sand it back again before your primer coats... It's what I would try, but it's just my suggestion...

dag65
07-18-2003, 05:51 PM
Had this happen on the fender of one of my Mazmanian Willys. Sanded the heck out of it and it came back. So on the next one i sanded a little more carefully , primed, then I sprayed a guide coat and sanded the primer which revealed the line again. I used a filler primer and shot several caots in that area alone and let it dry for over a week. This time no problems.
I think your mold line must be raised, it appears that the paint and clear coats actually penetrate through to the plastic and cause that seem to raise a bit. This can also happen when you have sanded off a detail such as a door handle.

RallyRaider
07-18-2003, 06:02 PM
I've had this happen before but only on the primer coat, using lacquer based paint. I think the solvents in the paint etch into the plastic and becuase the mold lines are grained differently or something the reaction is stronger and the mold lines reappear.

Another coat of primer and a bit of sanding solves the problem. Perhaps you needed to lay down a thicker primer coat? Not much help now since the clear won't hide anything and sanding down to the metallic will look very ugly.

Only way I can see to correct it is to sand back and respray. Terrible luck :frown:

flyonthewall
07-18-2003, 06:05 PM
Grey primer is better for showing up mold lines and defects, you can miss alot of problem areas with white primer. If it has to be white give it a spray of grey first to check, the white primer will easily cover the grey anyway.

sugarcaddy
07-18-2003, 06:39 PM
I have this same problem all the time! Best advice to give you is to sand the hell out of them and then prime. If they are still there putty the suckers then sand and prime! Works for me!!! :bigthumb:

Scott

Hiroboy
07-18-2003, 07:11 PM
http://www.spc.org.uk/misc/mold-lines003.jpg
Thanks guys, it's out of the paint stripper, and sanded to hell and given a coat of grey primer, now drying in the microwave.
I'll have a look in the morning and let you all know how it going.

The picture above was shows what a nice colour it will be when finished
this was taken before stripping.

tazdev
07-18-2003, 10:01 PM
that colour is going to look real mint on that car. Hope ya don't get the same line problems

Hiroboy
07-19-2003, 04:21 AM
http://www.spc.org.uk/misc/mold-lines004.jpg
This is the progress now, Primed, Dried, 4 coats of paint airbrushed, still no sign of the mold lines yet (fingers crossed)

primera man
07-19-2003, 05:42 AM
Just from looking at the first pics they look depressed and not raised.
When you sand do you sand across the mold line and not along the length of the line ?

LaTtE`X
07-19-2003, 06:55 AM
If it doesn't work, a very thin layer of putty before the primer should do it.

hirofkd
07-19-2003, 11:53 PM
It appears to me that the body was not sanded well, and primer was too thin.
Metallic color is essentially translucent, so if you don't smooth the body thoroughly enough, mold lines could show up, and it's enhanced by clear coat.

This could happen to anyone, who's going to use metallic, so it's better taking an extra caution.

Try using Mr. Primer or equivalent products, and hand brush it over the mold lines to make sure the lines are gone. Then, make the primer coat opaque enough.

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