Over at Model Airplane Maker, Chris cogitates putty and ways of addressing its shortfalls. He even includes a video demonstration of his seam filling techniques:
Absolutely nothing! Well, at least when it comes to dealing with massive gaps. There was a time when I would gather my allowance and bottle return …PUTTY! Huh, Yeah! What is it good for?
Angst over ghost seams shows up everywhere these days, particularly on plastic modeling podcasts.
Chris advocates forgoing old-school putty, more or less, in favor of preventing cracks and gaps in the first place with better assembly and liberal use various clamping techniques.
A logical next step in Chris’ very sound advice to avoid gaps altogether is to use the solvent-based welding action of styrene cement and strong squeezing or clamping pressure to create a ‘squish’ of molten styrene that, when thoroughly dry, can be scraped and sanded away.
Shep Paine described the ‘squish’ technique in one of his early books, and it was a method that markedly ‘leveled up’ my own modeling, back before we borrowed that term of art from video gaming.
Chris then suggests skipping the putty altogether when gaps can’t be prevented. He describes a couple of methods that many modelers, including me, developed via trial and error.
First, he recommends filling egregiously large cracks with styrene rather than putty filler. Evergreen strips work well for this, and stretched sprue works in some instances as well.
Another styrene material that works well for gap filling is styrene strut stock, which has an aerodynamic teardrop cross section. The thin tail of strut stock can be snuggly wedged (jammed) into a gap and then secured with liquid styrene cement. Pressure applied immediately after cement application yields a bit of Shep Paine squish. Once dry, the tightly fit strut-and-squish combination can be sanded and polished away.
Unfortunately, strut stock has been hard to obtain of late, probably because of declining interest in vacuform kits and scratchbuilding of pre-jet age aircraft. If you see some strut stock, buy it—invaluable for gap filling, but you’re likely to fight one the few remaining stringbag modelers for it.
Chris also suggests alternatives to conventional putty. In particular, he suggests cyanoacrylate cement (AKA CA, or superglue) cured with accelerator. This is a sound technique with only a few easily manageable drawbacks. Besides being fast and gratifying, cured CA is stable and shrinkage free. Its one significant drawback is that accelerator-cured CA continues to harden after it cured, so it is critical to sand and polish in small, manageable segments immediately upon curing. Waiting overnight or a few days may result in glass- or ceramic-hard spots that are difficult to sand or scribe.
Meanwhile, a silver marker or paint pen is invaluable for showing sanding and polishing progress, regardless of filling method. The silver marker applies quickly without the hassle of airbrushing or a rattle can and dries very quickly to support fast progress on seam filling.
Chris mentioned using nail polish remover—acetone—to smooth and blend old-school putty while it was still wet, with the caveat that acetone also crazes styrene. What Chris did not explore was epoxy- and acrylic-based filling materials that can be smoothed and blended with water-moistened q-tips/cotton buds and paint brushes while wet.
My experience with two-part epoxy putty is limited, but figure modelers have been filling and also sculpting with it for decades, indicating its excellent strength and stabilty properties when dry.
Acrylic putty’s superpower is its water workability. Unfortunately, acrylic putty doesn’t have much use beyond some specific but common situations. Its limitation is that it is not particularly strong or receptive to drilling or scribing.
I regularly use acrylic filler putty offered by Vallejo and Deluxe Materials for specific filling applications such as corner gaps between wings and fuselage, armor plates, and an inconsistently fitting hatch or door. Multiple applications of the acrylic putty might be required, but using water to smooth and blend and remove excess acrylic putty also eliminates the risk sanding away adjacent detail.
In any event, I still don’t feel like I have foolproof seam filling game, and I’m always on the lookout for new techniques. I’m looking forward to the comments on Model Airplane Maker putty post, and hope I learn more about how to manage seams.