Never ending mold lines

[jmwallac]

I'm working on Tamiya's 360 Modena, and for the life of me can't remove the mold lines. They aren't ridges like I usually find. Instead they are little grooves.

I sanded with 400 to start, then primed the body. They were still there. Next I took a new #11 blade and scraped all the seams. The seams were filled with primer, so I scraped until the primer was gone. After another coat of primer, the seams showed up AGAIN! I've sanded and scraped pretty deep. As the primer dries, they seem to become more visible.

Is this ghosting? Is it possible the paint will not show this? I don't really want to paint it and find out it's still visible.

Primer is duplicolor white primer, which I've usually had great success with.

[patoffspyder]

Usually when I use duplicolor white primer, I put the gray sandable primer first. It covers alot more.

[jmwallac]

For my Revell models, I ususally use grey as well. But Tamiya is usually molded pretty precise and white will work.

That being said, after 2 sandings and 2 scrapings, the lines are as deep as they were when I started. I can feel them with my nail. I'm not sure what gives....

Anyone else have a problem with the seams on this one?

[ZoomZoomMX-5]

Originally Posted by jmwallac

For my Revell models, I ususally use grey as well. But Tamiya is usually molded pretty precise and white will work.

That being said, after 2 sandings and 2 scrapings, the lines are as deep as they were when I started. I can feel them with my nail. I'm not sure what gives....

Anyone else have a problem with the seams on this one?

Yes, when I used automotive lacquer (Black Gold HOK lacquers) on my 360 Modena all the mold lines kept coming back...I never saw it in the primer or the color, but when I put clear on the solvents in the paint crept down to the surface and caused ghosting. It was relentless until I switched to a milder clearcoat. That's likely what is happening to you. Either use a less caustic paint, or use a sealer that blocks the solvents from attacking the plastic. Get a spray can of Zinsser B-I-N shellac-based primer/sealer at Home Depot or Lowe's. It's best to decant/airbrush it between layers of lacquer primer (it must be applied over another primer, but you can topcoat over it). If you are limited to just spray cans, you must find a better nozzle. But this stuff does the trick, it works great as a sealer on persnickety kit plastic.

[jmwallac]

Originally Posted by ZoomZoomMX-5

Yes, when I used automotive lacquer (Black Gold HOK lacquers) on my 360 Modena all the mold lines kept coming back...I never saw it in the primer or the color, but when I put clear on the solvents in the paint crept down to the surface and caused ghosting. It was relentless until I switched to a milder clearcoat. That's likely what is happening to you. Either use a less caustic paint, or use a sealer that blocks the solvents from attacking the plastic. Get a spray can of Zinsser B-I-N shellac-based primer/sealer at Home Depot or Lowe's. It's best to decant/airbrush it between layers of lacquer primer (it must be applied over another primer, but you can topcoat over it). If you are limited to just spray cans, you must find a better nozzle. But this stuff does the trick, it works great as a sealer on persnickety kit plastic.

It's comforting to know I'm not the only one! Would filling this seam with putty or bondo help fill this crevice? I'm tempted to sand the plastic and hit it with the Tamiya TS spray without a primer....

ZoomZoom: what did you do to get rid of those moldlines after it was painted/cleared?

[drunken monkey]

thing is, he is describing ghosting, you are describing actual grooves.
they might not be the result of the same thing.
have you tried first filling the grooves with putty or primer before laying on primer coats?
don't forget to let that filling and coat cure properly as it will shrink as it does does so.

[ZoomZoomMX-5]

Originally Posted by jmwallac

It's comforting to know I'm not the only one! Would filling this seam with putty or bondo help fill this crevice? I'm tempted to sand the plastic and hit it with the Tamiya TS spray without a primer....

ZoomZoom: what did you do to get rid of those moldlines after it was painted/cleared?

I honestly don't remember that far back exactly what I did to kill the mold lines reappearing (and they did look sunken vs. raised, just a weird thing w/this kit), I know I wetsanded the clear/color smooth so that the lines disappeared and reapplied the color in mist coats and recleared several times, and it always came back during the clear stage, so either I switched thinners (a friend may have given me some faster drying thinner for the HOK clear), or I may have switched to Tamiya clear. Eventually the problem stopped, but I was about to destroy the model by backing over it with my 1:1 car and take pictures I was so PO'ed with it by then. It was a first-run Modena where not only did I have paint problems, but the glass didn't fit, everything on the clear tree was about 10% too large. It nearly drove me insane. But the engine, interior, and chassis were a breeze They retooled the glass after the first run I know after the Modena I was having similar paint disasters w/my GT3 and found that mixing Mr. Color Thinner w/my HOK clear paint would let it flow on nicely almost like enamel w/o blushing or causing the ghosting of mold lines. Ever since then that is what I thin the HOK paint with. But if I have a suspect model that I think might have issues, I will seal it w/B-I-N between the first primer coat and my first color coats. B-I-N is white and sands amazingly smooth, just wish it shot as nicely as Tamiya white primer.

If your plastic is already damaged by solvents even Tamiya paint could cause some issues, as it's stronger than most hobby paints. You have to tread lightly.

[rsxse240]

I'd suggest using a styrene safe primer, then an automotive "sandable" primer, masking around the difficult areas so you don't have to sand the crap out of the entire model. then sand and fill until there is no more line.

A good glazing putty should take care of this as well. Just remember not to sand all the way down to the scratch, or mold line as it will then ghost around the putty. Just build up around the scratch, then sand it down untill you have a good feathered edge. Lay down a coat of primer, sand it with some 300, or 400 grit, lay your base paint coat, let it dry then wet sand. by this time you should be able to just paint the body normally.

[jmwallac]

Well, I finally solved the problem.Sanded down to the bare plastic (again) and then sealed the seams with superglue. If brushed on lightly, it is actually pretty thin. After the super glue dried, I primered it and then sanded it smooth, blending outwards to get rid of any ridges.

Another few coats of primer and the seams are finally gone! The super glue finally cured the never ending mold lines.

Thanks

[rsxse240]

that is great! and a great idea to fill seams and gaps. I guess you could use some C/A accellerant to speed things up a bit and keep from sticking fingers together! haha

[jmwallac]

Originally Posted by rsxse240

that is great! and a great idea to fill seams and gaps. I guess you could use some C/A accellerant to speed things up a bit and keep from sticking fingers together! haha

I did have to sand out a few fingerprints....

[ZoomZoomMX-5]

Originally Posted by jmwallac

Well, I finally solved the problem.Sanded down to the bare plastic (again) and then sealed the seams with superglue. If brushed on lightly, it is actually pretty thin. After the super glue dried, I primered it and then sanded it smooth, blending outwards to get rid of any ridges.

Another few coats of primer and the seams are finally gone! The super glue finally cured the never ending mold lines.

Thanks

That reminds me of another trick to avoid ghosting learned from someone who does a lot of radical bodywork; when you've sanded the mold lines away (or removed trim or door handles etc), before priming carefully brush on a layer of liquid styrene cement, like Ambroid/Tenax or the Testors stuff. That "sets" and seals the styrene that's been sanded making the ghosting/bodywork issues stop. Those fine troughs you found were the result of the plastic swelling around the original mold line, the plastic swells up in the areas that were sanded because the surface had been breached by sanding, and that lets the solvents absorb into the plastic. The liquid glue gets the plastic surface memory back to that of the areas that weren't sanded.

Glad to hear it's finally smooth. Good luck w/it!

[Some_Kid]

When using Duplicolor clear you need to spray light coats first, because if you make them too heavy it will cause ghosting. In your i case i would light putty those mold lines to be safe, maybe even going over them with super glue to get it smooth. I hopes this helps and good luck.

[jmwallac]

Originally Posted by Some_Kid

When using Duplicolor clear you need to spray light coats first, because if you make them too heavy it will cause ghosting. In your i case i would light putty those mold lines to be safe, maybe even going over them with super glue to get it smooth. I hopes this helps and good luck.

Thanks, but I never made it to the clear stage. This was all primer. I did use the super glue to seal the seams and it worked great.

I've had great luck with duplicolor clear. The first model I built was a 1/12 scale motorcycle with full decals and I heaped the clear on like it was going out of style. 3 really wet coats about 5 mins apart and it didn't do a thing to the decals or the plastic. Beginners luck I guess.

[Some_Kid]

LoL i missed your post about the super glue. Yea ive been using super glue alot lately to fill scratches and what not, it works really well.