Gluing painted parts.

[seadude]

I've often read and heard that when gluing parts together that are painted (One painted surface to another), it is recommended to not use CA superglue, but rather white glue (Elmer's for example.). But sometimes when I use white glue to attach painted parts, they don't always stay together, even after days or weeks of being glued together. Are there any other better glues I could try using to glue painted parts together?

[PR19_Kit]

How about UN-painting the areas that need to be glued?

I'd never even think of trying it.

[seadude]

How about UN-painting the areas that need to be glued?

I'd never even think of trying it.

And what if some areas are as small as the tip of a toothpick? Or in really hard to reach areas? Then what? I don't have any tiny sandpaper tools to sand away paint for areas like that.

[PR19_Kit]

The primary problem with gluing painted parts is that you're relying on the strength of the paint-to-plastic bond to actually hold the part in place, and that bond isn't designed to do that.

That's why I suggested to remove the paint, the alternative being not to paint that area of the part in the first place.

[Weaver]

I always scrape the paint off bonding surfaces, even if the parts are tiny. You can use things like the tip of pointed tweezers or even a bit of stiff wire or copper rod.

[kerick]

The Elmers glue will not hold painted or unpainted parts. It works on porous materials best. The only place I would consider it is attaching canopies or headlight lens using glue that dries clear. Then its still not a strong bond.

Perhaps the concern about using CA to attach painted parts comes from the possibility of the vapors released by the CA causing a frosty white deposit. This often happens when gluing canopies or other parts that would not allow free air movement. I've not had a problem with that otherwise.

PR19 kit is exactly right about the paint to plastic bond. I always use enamel paint which I believe attaches more firmly to the plastic than acrylics. Putting stress on an acrylic paint bond would probably break the bond easily. That's not saying enamel paint is all that strong either.

The best option to me is to glue before painting or remove paint to glue. Now a small drop of Elmers in the right place could act as a masking material. Just pop it off after the paint is dry. There are other liquid masking materials out there. For me a new #11 blade can reach into small holes and the curved blade is good for scraping of paint in small spots. A very small drill bit in a pin vise will remove paint from locating holes.

[zenrat]

If you've used primer and cleaned the plastic then your paint should stay put.  Try 5 minute epoxy.  The only drawback might be mixing up the tiny amounts you'll need.

[Dizzyfugu]

I also think that the CA-on-paint does not work well because the glue is stronger than the paint that it adheres to, and model paint does not really bond with the plastic below, esp. acrylic paint/primer. So, with CA you might have a strong spot bonding, but the paint is actually the weak part.
White glue is just like acrylic paint. It does not react with the material, it just adheres due to its good/large footprint - but it comes apart easily under force.

Kit is 100% correct: best way is to use plactic glue on styrene, and just to clean the surfaces that are to be glued, and use the glue sparsely. Typically it reacts with the paint, so the results can be pretty ugly/messy and necessitate repair work.

Personally, I come to prefer a build-first-paint-later approach whenever possible. Has made, for instance, landing gears a much more stable thing. Than painting the parts first and fiddle them into place when the parts won't accept the glue well.

[NARSES2]

Now I agree with all that's been said but one thing I have done with some very small parts is to use a stronger glue, in my case Mr Cement Deluxe rather than my usual Mr Cement S. I apply this to both surfaces, in tiny amounts, and this cleans the paint off the surface and then welds it as normal. Used very carefully you can avoid collateral damage.

I must admit I am moving more to the paint after assembly method as described by Dizzy especially with parts that require strong joins. With this then small brushes or cocktail sticks are best used for painting. Personally I've not ha superglue muck up a pre-painted surface.

[zenrat]

Superglue while being strong is brittle and may not survive a sharp knock that a more flexible epoxy would.
I tend to build the main bits then paint then assemble and add fiddley bits.  Probably because that's how most people seem to build model cars and when you come down to it i'm a model car builder taking an extended detour into whiffing (and with absolutely no plans to get back "on track" yet).  If you have painted a model car body and got it nice and shiny and polished and cleared and looking far better than they ever did IRL then the last thing you want to do is to scrape off some of that paint to get to naked plastic to glue on a badge, wiper or aerofoil.

Important thing to remember though is there is no one right way, just lots of favoured methods.

[Hobbes]

Tiny parts are usually not structural, so I'm not bothered if the glue bond isn't very strong. When I bump against a small part, I'd rather have it fall off intact rather than break in half. I normally use CA to glue the part to the painted surface. Parts glued like this have survived several trips to Telford in the back of a car, that bond is strong enough for me.