Super glue as a seam filler?

It good for very small holes, dents or narrow seams but once it cured it is very hard to sand down.  I wait until it dries (but not cured) and then sand.  There are super glues just for gap filling.

My experience is the same as Marcus'.  I wait only about 1/2 hour to 1 hour (depending on how much you need to apply), then start sanding.  It makes things a whole lot easier than letting it dry overnight.

Good luck.

I also find that scrapping with the back side of an Exacto blade helps knock a supper glue seam down, then finish with sanding Just don't go to far.

I've been doing that procedure for years.

I've never had much luck sanding dried super glue. Even when I try within 30-60 minutes.

It's not the ideal seam filler.

There is a trick to it that I learned here on the Forum a while back. Only fill about two inches or less of the seam at a time. I use Zap a Gap medium CA applied with a rounded toothpick. Then I hit the CA with accelerator  ( I've got a big bottle of liquid accelerator from MicroMark) applied with a micro brush. Sand immediately with successively finer grades of sanding sticks. The CA will be set hard enough to sand but not  so hard as to be difficult.

All super glues are not alike, so generalizing isn't very helpful. Personally, I've never had the experience of the glue being harder than the plastic. The medium and thick viscosity glues have a filler, which is usually PMMA (the same acrylic polymer found in Plexiglass). I think this filler is responsible for the hardness complaints--PMMA is a very hard plastic.

So why haven't I had a problem with the stuff being too hard? I use the thin stuff for seam filling--it has no filler. For bigger gaps, I start with putty or strip styrene, but then I top it off with some thin CA. Then I sand it smooth as soon as it dries (the thin stuff dries really fast, so I don't use any kicker).

The thin stuff seems to flow into small nooks and crannies better than the thicker stuff. It also sits down flatter on the surface, which means I don't have to sand as much. I save my medium CA for sticking stuff together.

Well I have.  I used the Micro-mark CA glue once on a seam and left it over night.  I ended up using a metal file on it.  It was so hard the sand stick just slide without biting into it.  I don't let sit that long anymore.

If you are filling a small enough gap in a seam, you may be able to apply it smooth enough that you don't need to sand it.  Also, for smoothing seams, I use a flat needle file- it is agressive enough to cut both the superglue AND the styrene, yet fine enough that primer will fill any tiny residual scratches.  Usually the result is great.  Those files are equivalent to very fine sandpaper as far as smoothness, but as agressive in removing material as coarse sandpaper.

WOW. I have never had this experience. I use Zap-a-Gap to join seams all the time. I use it on the seams of gun barrels and other long straight runs. I run a bead along each edge with a toothpick, squeeze the pieces together so a little oozes out and let it set, then sand whenever I get around to it. days later sometimes. The super glue sands right down, and the seam is almost completely filled. Follow it up with some Mr. Surfacer 500 and the seam is completely gone. I haven't found anything that works better.

I dunno, I've had the super glue get as hard as Chinese arithmetic when I've waited a day or so.  Now I try to get on it much quicker...

Gary