I used to assemble the entire kit and paint.
For the 1st time, I’ve painted small parts of an AFV (e.g., shovels, ammo boxes) before cementing them to the hull. Do I have to scrap off paints from the areas where I will apply a cement? Or, can a cement work through layers of paints? FYI, I use Tamiya xtra thin and Gunze liquid cements.
Its reccomended you do for a firm hold. But if your not worried about how hard its going to stick down, not really. I dont normally. If its a strctural peice i will and touch up later. but for the most part i dont.
Those are solvents so they will not work through paint. They are good though, as you know.
What does work is Cyanoacrylate (super glue). Beware though- the bond is really only as good as the paint is bonded to the plastic.
I tend to break up the process. For gluing wings and hulls etc. together, where scraping and sanding is to follow anyways, solvent glue gives a better bond IMO.
For tacking on details, which are usually prepainted as you say, superglue.
Often for a bigger surface, like a white superstructure to a wood colored deck, scraping off paint is necessary.
Both have their uses.
The Tamiya (and I assume the other as well) will (or at least should) eat right through the paint given enough extra liquid (shouldn’t nead much). Personally if I am gluing an already painted item I never scrape the paint, use the amount I would use if it wasn’t painted and dont have problems with to much glue or not sticking/cementing/gluing
Andrew
Yes…
Use superglue. Don’t try to use regular solvents. You’ll most likely wind up melting the paint together, which will stick the parts together, but you’ll have a weak joint, and they may fall off in time.
Get yourself some superglue.
I have cementede painted parts together and had no problem. But I prefer to use CA, it’s stronger.
When i doubt …scrape the paint off .
Solvents such as Tenax will dissolve acrylic paints and really make a mess. Use CA glue to avoid this, but best is to scrape off the paint no matter what kind of glue you are using, and use the smallest amount of glue possible.
Thanks for the replies. I’ll just scrape off paints. It’s no big deal at all.
CA works to a point Doog but a weakpoint of CA is temperature and skin oil. I’ve seen bonds lose their bond above 90 degrees Fahrenheit and parts literally pop off at temperatures below freezing. And if your going to scrape paint do the locating holes first. Use a drill bit from a pin vise put it in the hole and wiggle it arounda bit and it sould clean out the hole.
[dto:]
Ron
Newbie here. I was considering putting up a new post basically asking this same question and came across this thread by way of searching.
Anyhoo, I’m currently working on my Atlantis 1/8 Phantom of The Opera. Within a few days now, I’ll be taking the plunge into the world of airbrushing for the first time. I want to spray a primer coat on all parts. Thing is, I don’t want to assemble all the parts yet as, in my mind, it will be easier to paint some parts before I cement them in place. Long story, short……I’ve decided to mask the join locations of said parts that aren’t attached yet and I’m curious if any other modelers use this method.
On a side note……I’m amazed that this basic question isn’t addressed in any of the “How To” literature I have.
Thanks and cheers,
Mark
Solvent based glues/cements should never bee applied to paint.
However, small parts (where there will not be any stress/load on the glue joint) can be attached with a small amount of super glue or white/pva glue without scraping the paint off first.
Wow, zombie thread! 
Yeah, you’ve seen the various replies. It depends on the materials and glue.
When I am gluing styrene to styrene, for which I use styrene cement, I make sure the attaching surfaces are clean, free of paint. If I’ve painted parts before cementing, that means scraping the paint away.
And even with other types of material and glue-resin or white metal, say, and CA glue or 2-part epoxy-I still prefer to glue to cleaned surfaces. Again, that means removing paint sometimes, if I have painted parts before assembling.
About the only adhesive that won’t attack a material chemically is white glue.
Exactly. Generally, scraping the paint off with the back of an Xacto knife is no big deal. Another option is a cotton swab/Q-tip dampened in a hot solvent like lacquer thinner – it just wipes acrylic hobby paints off effortlessly. Just… be careful to not get it on your finished areas.
Although I mostly work with smaller miniature figures, I think building and painting in subassemblies is an excellent method. Just think ahead about which parts you definitely want to paint before assembling, and which you can do after. Sometimes this may mean building out of the order the instructions suggest. For example, any seam that will be in a visible area after assembly should probably be glued before painting, or it will show. So, instead of spraying each individual part before building, I usually end up with 2-3 major assemblies that I can then paint and assemble.
With all that said, airbrushes are very good for getting nice coverage even on hard-to-reach places. And if it’s so hard-to-reach that you can’t spray it with an airbrush, you probably won’t be able to see it on the finished model anyway. 
Hi Mark, I sometimes mask off areas to be glued. For small holes I want to mask (landing gear attachment points for example) I use liquid mask (maskol is my favorite). Also, for things like fuselage seems, I don’t mask it, but after airbrushing the interior color, I immediately wipe the paint off the seam with a Q-Tip/Cotton swab dipped in 91% IPA (This works with paints like Tamiya, Gunze, and probably any similar formulated paint).
LOL, I guess the OP was a while ago. Well at least I am not to blame for waking up the zombie this time
I agree with Mister Meester, keeping paint off gluing surfaces not only makes for better joints but avoids the paint film from interfering with the fit of the parts - newer kits often have very tight tolerances and getting paint in the joints can cause “stack up” problems. Masking or cleaning the paint off as you go will prevent this.
Konrad