gaps. GAPS!

I want to make sure I understand. You are using super glue to, well, glue the pieces together as well as fill the gaps? Then just sand?
 
I think the guys are saying to just use the super glue as a gap/seam filler, but to use normal liquid glue for the actual assembly. I have used CA as a filler before and while it works well, the drawback I find is that it sands very differently than the surrounding plastic and can be problematic if you aren't careful as the two surfaces will have a different appearance, even under paint.

The only reason that I know that you use baking soda with super glue is because it acts as an accelerator, so even if you use the thicker gap filling glue you can still sprinkle the baking soda to cure it instantly if you want. This allows you to handle the model without getting stuck and/or sand it right away instead of having to sit around and wait for it to cure naturally.
 
Psylow said:
I want to make sure I understand. You are using super glue to, well, glue the pieces together as well as fill the gaps? Then just sand?
Click to expand...

For a styrene-to-styrene assembly I would normally use solvent cement to join the pieces together and then use filler as needed. Superglue is a great filler as it has more inherent strength then putty or surface primer; this can come in handy as it re-enforces large joints during the sanding process. There's nothing more annoying than eliminating a large seam (fuselage halves, for instance) and then have the glue join fail due to buckling, oversanding or rough handling (that's my trick ;)). Try this as a general guideline: for a hairline crack, use Mr. Surfacer or something similar. For a seam as wide as the thickness of a sheet or paper up to 1mm or so, use putty. For an seam or gap larger than 1mm, use super glue. The trick with super glue is not to rush the process, apply a little bit at a time and let it dry between coats. I made a handy tool for applyling supergue which is basically just a pin stuck in the end of a chopstick. This allows me to apply the superglue a drop at a time and drag it along the seam, filling the seam evenly. Using the multi-layer approach also prevents you from applying to much... if you over-apply, you'll just have to sand more off. I agree with Ken Abrams, superglue is harder to sand than the surrounding plastic so you have to be carefull that you're sanding the glue down to the surface around it and not gouging into the plastic... it's not that hard once you get the feel for it. As for the surface appearance problem, this can be overcome by applying a surface primer like Mr. Suracer AFTER you've sanded down the superglue to your liking. By applying surface primer over the superglue and surrounding plastic, you'll fill in small surface imperfections and be able to feather out the filler much more subtly.
 
I don't like using super glue so I avoid it as often as I can. I use Tamiya putty or spare styrene to fill gaps. I use Tamiya Basic Gray or White to fill small gaps. Make sure to apply it in thin layers and wait for the bottom layer to dry before you apply the next one. For larger gaps or reshaping I use Tamiya Light Curing Putty or styrene. I have an assortment or stryene rod and sheet. I find one that fits the gap or trim one to fit, lay it in the gap, and then run liquid cement along it.
 
Yes, a drawback in using CA (super-) glue is that it can be harder than the surrounding material when cured, and in sanding the glue, you can damage the surrounding area or remove the material, when you don't really want to.
 
the Baron said:
Yes, a drawback in using CA (super-) glue is that it can be harder than the surrounding material when cured, and in sanding the glue, you can damage the surrounding area or remove the material, when you don't really want to.
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This is why I won't use CA. I want my seam filler to be softer than the surrounding plastic. That way I remove it first then the plastic.
 
sorta late to ask this but we are talking about regular run of the mill super glue right? I already have some testors cement for models. Is that only good for joining pieces together not so much gaps?
 
Super glue/CA. Testors cement, like other plastic cements, melts the plastic and the melted plastic hardens to form the bond. You can't use it for filling gaps, unless you fill the gap completely with scrap styrene.
 
Most superglues (cyanoacrylate or CA for short) are created equal, the difference is mostly in viscosity. Your hobby shop will carry several thicknesses of CA. The thin types are great for attaching photo-etched metal or thin veneers of plastic, etc. The thicker types are better for gap-filling since the surface tension will hold the glue in place as it cures and it won't run all over the place before it dries. Applying baking soda to the bead of superglue will accelerate the curing process.

NEVER, NEVER, EVER try using solvent cement to fill a gap. NEVER. It's impossible for the solvent to fill the gap and at best you'll weaken the join; at worst, the solvent will flow through the gap and slop around inside the model, running out at another opening in the plastic... usually right where you're holding it and then you'll have a fingerprint melted into the surface of the plastic to contend with.
 


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