What causes PPS?

Post painting seams, that is.

I’m working on a couple of Eduard 1/48 biplanes. It’s my first venture into 1/48 aircraft and 1/48 biplanes. One is an Albatros DIII for the One True Scale campaign. That’s painted and waiting for decals to arrive. It’s holding together fine.

The other is a Nieuport 17 that a friend of mine started and didn’t want to finish. I had to do substantial seam repairs on the top and bottom. I covered almost the entire bottom with mr surfacer - a couple of coats and sanded it smooth. The top was better - not a very noticeable seam, but filled with mr surfacer and sanded smooth. Close check after priming and the seams were gone. Painted and still no seams. So I sealed it and put decals on and all is good. Tonight I was working on rigging and noticed that both seams had reappeared. The one on top is barely visible but the one underneath is quite noticeable. How did that happen?

I had this happen once before on a hurricane. I was pretty convinced that a seam reappeared but talked myself into thinking I just hadn’t been thorough enough. This time, I’m sure it was gone and is now back.

Help?

Phil,

I too have had this happen with perfectly smoothed surfaces having seams reappear later. This can be a problem with putty type seam fillers. Mr. Surfacer is lacquer based, and as the lacquer dries the filler shrinks slightly. This isn’t a problem unless you smooth it before it is COMPLETELY cured. Even though dry to the touch, putty fillers can still be moist under the surface, so even when smoothed they still can shrink as they completely dry over time… resulting in the seams reappearing. One way to prevent this would to be to make sure the Mr. Surfacer has completely dried before smoothing the seam, but this can take weeks. My solution to this was to switch to cyanoacrylate (super glue) as my seam filler, as it is tough and doesn’t shrink.

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Ah yes, the dreaded ghost seams. When I do my seams, I like to use the leftover sprues cut into small nuggets and put into a almost empty jar of Tamiya extra thin, some call this sprue goo. Let it cure completely, and then sand and polish.

(4) ep302 - dealing with ghost seams - YouTube

Some very good information in this video, those ghost seams are a real thing and tend to pop up worse when you’ve got your paint job almost perfect!

Cheers, D

What @TimReynaga says. All of the solvent based fillers will continue to shrink until they are totally cured which can take days or even weeks. They’re OK for some uses, but for large seams and gaps, you’ll almost always get the dreaded “ghost seam shrinkage.”

I suggest using CA and micro-balloons (or baking soda or some other powdered filler). Once cured, there will be no further shrinkage and the surface can be polished very smooth. Spread and push in the powdered filler material, then add the CA, allowing it to soak in. Finish with an accelerator to speed up the curing. As soon as the CA filler is hard, you can finish smoothing the seam.

If the powdered filler chips out or the CA hasn’t soaked in leaving voids that spill out when opened up with the tooling to smooth the seam, then just reapply more CA and accelerator and repeat. Sometimes the powdered filler can leave a lightly pitted surface that can’t be polished. Again, just apply another coat of straight CA, accelerate the cure, then repeat the smoothing work.

The powdered fillers help fill large gaps and seams, but the main purpose of the micro-balloons is to make the CA filler lighter, especially necessary for flying models. For static models, filling the gap with styrene is a better option if the finished surface has to be “baby’s behind smooth.”

The major downside to CA as a filler is that although it will not shrink any more the longer it cures, it does become harder over time. This means that you can easily tool away more of the surrounding plastic than you want while trying to tool the CA filler flush and smooth. The best practice that I’ve found is to finish the seam as soon as the CA has hardened, and if that’s not possible, finish up the seam as soon as you can.

You can wet sand and polish CA to be almost as clear as glass, but it can be tricky to use around clear parts because of fogging because of the outgassing it does when curing. However, it can be smoothed to as fine a finish as you want.

Prefilling the seam with styrene strips, rod, or stretched sprue so that only the minimum amount of CA filler is needed also mitigates the potential problem of over-tooling the surrounding areas while smoothing out the CA filler.

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Thanks for the feedback, folks. Interestingly enough I was watching a video the other day from a guy who fills seams with a mix of CA glue and metal pigments. I don’t think he said anything about ghost seams - he was mostly interested in building things up to sand against rather than sanding a curved surface flat. I’ll go back and watch again.

And I’ll watch the vid at your link Reg, or D, or …

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Plan b, wait a month to paint while you start another kit. Any repairs will be minor.

I’ve used stretched sprue along joint seams. Saturate just the stretched sprue with liquid glue (be careful not to get glue runs onto the model’s surface) and when it’s soft squish it down flat and firmly into the joint. It helps if you use sprue from the same kit so that the plastic is of the same quality and color. Leave it overnight to completely set up. The next day it should be solidly welded to the model and have become part of it. Sand and polish smooth.
:smiley:

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The problem is called… patience, or the lack of it. Just wait long enough and let things that need to cure: putty, paint, varnish… more than enough time (read weeks in some cases) and your problems are solved.

:grinning:

By the way, I use Tamiya putty. For wide/deep seams/gaps I add a thin layer, let it cure, add another layer …

A tube lasts a long time.