Mold Line frustration

Hey everyone!

I'm having a hard time removing mold lines. The way I'm dealing with them at this point is

* I'm sanding them down with 220 grit then 320 then 500 then 800 then 1000 grit sand paper

* then I'm shooting duplicolor filler primer
* then two coats of tamiya primer

If I'm VERY careful at feathering out my sanding marks with the next level of sand paper.

When the paint lays down, it shows the sanding marks as what I like to call 'burn' marks.

Then the mold lines show up again also.

It is difficult to maintain the body character lines and get rid of the mold lines at the same time.

Am I using too heavy a grit of sand paper to start?

They show up particularly with thinned down automotive, decanted tamiya sprayed through an airbrush and they are even worse with metallics.

What are the tricks for getting rid of mold lines without sanding them and taking the risk of leaving sanding scratches and then have to scrap the bodies? :banghead:

thanks for your help

The surface is probably prepared just fine before you put the primer on. But the primer/paint/clearcoat might be too ¨hot¨ on the particular plastic which you are painting and therefore the mold lines reapear since it attacks the plastic. The only way to prevent this is to use some kind of sealer.. I found out that automotive 2k epoxy primer works well in such cases.

The surface is probably prepared just fine before you put the primer on. But the primer/paint/clearcoat might be too ¨hot¨ on the particular plastic which you are painting and therefore the mold lines reapear since it attacks the plastic. The only way to prevent this is to use some kind of sealer.. I found out that automotive 2k epoxy primer works well in such cases.
I totally agree, use different primer.

what is a good primer to use under hot paints like automotive paints. I didn't know there were any better than tamiya, though, I'd like to find one that gives me a nice smooth base and fills any small sanding scratches or mold lines.
Thanks for your help you guys

what is a good primer to use under hot paints like automotive paints. I didn't know there were any better than tamiya, though, I'd like to find one that gives me a nice smooth base and fills any small sanding scratches or mold lines.
Thanks for your help you guys

I use duplicolor grey primer sealer, and it works great. it sprays very fine and doesn't build up heavy, then I spray automotive basecoat and clearcoat and I have never had any issues. if you need a filler primer I would recomend the duplicolor high build primer surfacer, just make sure you put the sealer on before or after the high build formula, I put mine on after just before basecoat. both of these primers are very inexpencive for the amout you get and how long they last. hope this helps.

also I usually sand my mold lines with 400 then 600 grit sanding sticks.

Steve

Before applying any paint seal the plastic with a coat of Future. Try airbrushing it or carefully wiping it on. If you need to try again just take it off with ammonia. You can spray any paint over it. It also protects from color bleed like when you paint red or yellow plastic. Check this link for more info on using Future. http://www.swannysmodels.com/TheCompleteFuture.html

:runaround:great link :bananasmi

What are the tricks for getting rid of mold lines without sanding them and taking the risk of leaving sanding scratches and then have to scrap the bodies? :banghead:I eliminate mold lines without sanding them at all. I have three color coded pin knives with #11 blades installed. The blades vary from new, to dull, to disgusting. I eliminate the lines by using the dull blade sideways with a scraping motion. You will need a strong light source to ensure that you are hitting the target such as a halogen desk lamp. This method, when done properly, will leave only a thin strip where the peak of the mold line once was. I continue scraping until the strip blends with the rest of the surface. I then follow up with my normal surface prep procedure of generalized sanding with 800 wet over the entire body and have never had any trouble with sanding scratches.

You didn't ask about this but I'll also add that I remove my gate nubs with the new blade. I slice off small pieces of the nub in alternating directions so the plastic doesn't tear away. With a bit of practice (and bright light) the knife will eliminate the gate mark entirely.

In my opinion, anything coarser than 800 applied wet to a car body is asking for trouble. Sanding sticks are way over rated.

... I remove my gate nubs with the new blade.
Ouch! Sounds very painful :evillol:

In my opinion, anything coarser than 800 applied wet to a car body is asking for trouble. Sanding sticks are way over rated.
:iagree: :1:
I too have found that 800/1000 grit paper and the knife scraping technique are more than sufficient to remove mold lines. However, I almost never remove them fully the first time round so it is always good practice to give a light dusting of grey primer which will immediately show how effective round 1 has been :)

Check this link msg #6 http://www.modelcarsmag.com/forums/index.php?showtopic=22834&view=findpost&p=207738