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Those reoccuring "Ghost" seams


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A friend and I occasionally debate those "ghost" seams that keep coming back after seams are glued, filled and sanded. A week or two later the seam has a visible recess that of course is made worse to the eye when painted over.

Does any one have products they use that solve this problem. And a debate on the subject is of course welcome.

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Glue it, fill it and put it on the shelf for a few weeks. Some putties take a really long time to fully cure. 

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Use stretched sprue or 'sprue gloop' made from the kit sprues. As they are the same plastic as the kit, they behave in the same way as the kit parts being filled once set. After that, I just use Squadron Green Putty to fill any smaller imperfections and, if necessary, a wee dab of Mr Surfacer.

 

Mark.

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10 hours ago, bmwh548 said:

Glue it, fill it and put it on the shelf for a few weeks. Some putties take a really long time to fully cure. 

 

3 hours ago, Harry Lime said:

Use stretched sprue or 'sprue gloop' made from the kit sprues. As they are the same plastic as the kit, they behave in the same way as the kit parts being filled once set. After that, I just use Squadron Green Putty to fill any smaller imperfections and, if necessary, a wee dab of Mr Surfacer.

 

Most of my recent builds have been using Tamiya "light green cap" liquid cement with Tamiya or Mr Surfacer paint'primer. And yes sometimes the parts have sat literally over a month before I sand. Sanded perfectly smooth, then a week later the seams start to reappear as sunken lines. And yes several applications, sanding, waiting, filling again. Particularly on one recent project.

 

It has been many years since I used Squadron Green Putty but never remember this problem. As well about 40 years ago when I built so many Monogram kit, again I never remember the ghosting of seams. I was wondering if it is actually the plastic being used in most current kits.

 

Thank you for the comments and would like to hear from others if they have much success.

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I think it's just the putty you're using. Keep in mind there are a lot of different ones, some can get rehydrated by the primer/paint and you'll get a visible seam.

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It may well be the primer having an effect on the putty as @bmwh548 has suggested. I had that problem s few years ago. I was using Alclad primer but I cant recall what putty I was using. I know I switched to Mr Surfacer 500  as a filler with Ultimate Primer and I havent had that since. I'm sure there are those that can explain the chemistry.

Mark

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Squadron green is the worst culprit for this, I have read on several forums that it continues to shrink up to 6 months after application, Personally I have had issues with the stuff in the past so I changed to using Tamiya basic putty, much better result. 

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Squadron Green Putty was forever doing this to me. I have stopped using it and now use Mr Putty R, Mr Dissolved Putty, Mr Surfacer and haven't had that problem since.

I will also use Superglue to fill seam lines along long runs like the tops of fuselages if there is a ridge or gap that keeps reappearing, scribe out the joint a little then run thin Superglue in from an old craft knife blade. Don't let it set overnight but give it an hour then sand it flush.

 

Duncan B

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Any solvent based putties are for me are a thing of the past. I don't use them.

 

My method:

 

1. I spend quite some time on making good joints, sanding faces, removing location pins and adding new location with tabs of styrene stock if required. 

2. I mask the joint if I am doing interior spraying to eliminate that oozing coloured glue coming out at a glued joint. 1 minute's work for a stronger joint. 

3. Glue with Tamiya Extra Thin.  

4. Careful with clamping. I find side clamps on a fuselage opens the joint rather than closing. I find pegs on a wing open the joint. You need to clamp right on the edge. Nearly impossible.  I like my fingers, rubber bands and tape. I'll hold the joint and work along with the Extra Thin using a razor blade to open the joint slightly if necessary. I want to clamp once and use just enough glue to make the joint. Minimise softening back from the joint.

5. If there is a significant gap, which you will know about in advance from step 1, fill with shaped polystyrene (for me option 1), CA/Talc (option 2)  or Milliput (kept in the freezer, 30 mins on the bench and I can use it).

6. Normal seams - CA/talc for wider gaps or straight thin CA on hairlines or pits. Seems to be a lot of unnecessary worry about CA it's great for getting into the sanding quickly and feathers beautifully with no shrinkage. Absolutely eliminates any issue with the Eduard Mk IX/XVI Spitfire cowling joint.

 

Ray

Edited by Ray_W
typo
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One thing I've found as a potential cause of the dreaded "ghost seam" is that I've filled a seam with a solvent based putty, sanded it smooth and it looks great, I then sprayed it with a primer, such as Mr. Surfacer 1500 then light sanded for a smooth finish and everything looks great. Then I go through and spray a lacquer paint, like MRP, over the top and all of the sudden the seam starts appearing again in spots. My likely conclusion is that the lacquer paint reactivated or softened the solvent based putty just enough to allow for it to settle slightly. To solve this issue, I've started sealing areas where I've used putty with an acrylic primer, like Stynylrez and let it fully cure (not just dry to the touch) but fully cure, overnight in some cases, then coat with Mr. Surfacer. Since switching to this method, my problem of ghost seams are not an issue any longer.

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On 22/07/2020 at 18:11, jelliott523 said:

I've started sealing areas where I've used putty with an acrylic primer, like Stynylrez and let it fully cure (not just dry to the touch) but fully cure, overnight in some cases, then coat with Mr. Surfacer.

That's interesting - so you use two primers? I ended up switching to an acrylic primer for the same reason but I use that over the whole model. Is there a reason you apply Mr Surfacer as well?

Mark

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  • 2 weeks later...
On 7/28/2020 at 10:57 AM, Mark Harmsworth said:

That's interesting - so you use two primers? I ended up switching to an acrylic primer for the same reason but I use that over the whole model. Is there a reason you apply Mr Surfacer as well?

Mark

For awhile I was only using acrylic primers, and tried several (AK Interactive, Ammo of Mig - before they came out with One Shot, and Stynylrez). Stynylrez is what I ended up using for the longest time. My primary reason for switching was the smell from lacquer based primers. Unfortunately, with the AK and early Ammo stuff, I was having a hard time getting good adhesion, I had much better luck with Stynylrez, which is what I use now. The reason I will spot-prime an area where I've used a putty, like Tamiya, Mr. Hobby putty, Squadron, etc is that I find the lacquers can "reactivate" the putty making it soft and can tend to lead to ghost seams. With the acrylic primer over that, it tends to seal the putty so there is a barrier between the lacquer paint and the putty and it doesnt seem to reactivate. It also helps to do lighter coats of paint so that it dries quicker.

This is what works for me, there is no scientific proof that what I'm doing is helping, but its just something I noticed and theorized on.

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  • 2 weeks later...

I use a mix of cyanoacrylate glue and talc as my filler, and it doesn't shrink, using as it does a chemical reaction rather than a solvent. Try it to see if it helps your ghost seam issue

 

Cheers

 

Les

Edited by lesthegringo
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By the way - curing time for this method is minutes, although do all your rough sanding the moment it is hard enough to do so to make the sanding easier. You can alter the mix of talc to Cyano, but the more talc you use, the more difficult it is to stick and the crumblier it can be, but will sand more easily. Using more cyano will make it harder to sand when fully cured, but bonds really well and is better for tight gaps as it will flow into them better.

 

Whichever you use, once cured, when you sand it back there is zero shrinkage, and because it is fast you can address difficult seams very quickly. Doesn't react to any paints I have used either

 

Les

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  • 1 month later...

 

On 19/08/2020 at 06:54, lesthegringo said:

I use a mix of cyanoacrylate glue and talc as my filler

Me too, sometimes. However, I realized that if the talc used does not have extremely fine particles ("coarse talc"), and/or if air is trapped in the mixture, after sanding, small micro-holes may appear on the sanded surface. But in general this is a good cyano-putty.

 

On 15/07/2020 at 11:07, Harry Lime said:

Use stretched sprue or 'sprue gloop' made from the kit sprues. As they are the same plastic as the kit, they behave in the same way as the kit parts being filled once set.

I also use stretched sprue, especially when the seams to be filled are large (very wide and/or deep). I glue the piece of sprue in place (i.e., over the seam) using any glue (not too dense, not too liquid) suitable for polystyrene. After drying well, just sand until the surface is even. If neccessary (visual inspection, including gently running the fingernail over the seams to check for bumps or recesses) I use cyanoacrylate (medium density) for a final finish.

 

Most of the time I use only pure cyano to cover the seams (laziness 😜).

 

 

 

Edited by Convair
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7 hours ago, Convair said:

 

Me too, sometimes. However, I realized that if the talc used does not have extremely fine particles ("coarse talc"), and/or if air is trapped in the mixture, after sanding, small micro-holes may appear on the sanded surface. But in general this is a good cyano-putty.

 

 

I've been reflecting on this whole issue for a while now, and have come to the conclusion that maybe the modelling supplies companies are missing a trick.

 

What are the reasons that we use cyano or a cyano / talc mix? They have fast curing times, very little shrinkage as they use a chemical cure as opposed to outgassing a solvent, they bond very well to the surfaces so there is no chipping, they can be used for multiple gap sizes by changing the mix, and they can sand to a super feather edge that disappears under primer.

 

The advantages of cyano on its own is that it will wick into tighter gaps, providing mechanical strength to the bond plus going in far enough that you are unlikely to break through to the other side. It also scribes very well and can be shaped to fine points, allowing the tips of nosecones, missiles, and wing tips to be recreated. The downside is that it does not do larger gaps on its own, plus once fully cured it can be a devil to sand, meaning you have to careful not to sand the surrounding areas too much. It also cures more slowly and less completely in larger quantities required by wide seams, unless you resort to kicker. That's where the talc comes in, as it makes the sanding process easier, and also helps the cure with larger quantities, at the expense of toughness and the possibility of air bubbles or inconsistent mixes. It also doesn't scribe as well.

 

But fundamentally for me the reason I use it is the curing speed, and I almost always use it with some talc for ease of sanding. There are a series of nice videos on Youtube by quite a few good modelers out there, and one series is by Will Pattison who is a great exponent of 'sprue goo', which as Convair above points out is bits of sprue dissolved in Tamiya extra thin or similar. His reasoning for his usage of it is that the best material for filling a gap is the base material, and when the seam is properly addressed with it you will have no ghost seams and any sanding and scribing will be lie working on the parent material. It is a valid argument, but one of the common complaints about using sprue goo is the time it takes to properly harden, which is a function of how long it takes the solvent to gas out of the styrene. His view is that it takes too long because people apply too much, which will a ) increase the curing time and b ) increase the chances of shrinkage and ghost seams reappearing. If you use a minimal amount, he says, you can be working on sanding that seam in as little as 8 hours.

 

A good point, but here is my problem. When I get the urge to do modelling, one of the last things I want to do when I am in full flow is suddenly stop and put everything aside for at least eight hours; I want to get on with it hence the cyano / talc, as I can be back working on the seam in minutes without losing the momentum. I can fill, sand, see imperfections, fill, sand, see some remaining imperfections, then fill and sand one last time, all in 20 minutes or so. I would be willing to bet a large amount of cash that I am not alone in that. Now, if I know that I will not be back to a particular model for a week or so, sprue glue makes great sense, as it has the benefits quoted above.

 

So it has me wondering why the modelling companies have not developed a type of cyano that has the advantages of cyano, but without downsides. If it could be made so that it cures to a plastic consistency similar to styrene, that would avoid the use of the talc, make a more homogenous material and would then be easier to sand, more consistent to scribe, adhere well, not shrink, and if available in thin and thick (gel) consistencies could meet the criteria for narrow and wide gap filling. I know that various viscosities of cyano already exist, before anyone points it out - the problem is that they all cure as hard as nails, with the same sanding problem.    

 

So how about it - a 'plasticised' cyano for filling?

 

Les

Edited by lesthegringo
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