How to prepare painted surface for gluing

[PHPaul]

I did a search in this forum but didn't come up with anything specific to my question.

I have painted the cab for my log truck project.  I sprayed Rustoleum paint which I assume is enamel.  Next step (after paint cures completely) is to glue on various bits - clearance lights, air horns, mirrors, muffler brackets, etc. 

I know that glue works best on clean plastic, but removing the paint for the tiny contact points of the mentioned accessories seems like a non-starter.  Gluing them on before painting is also obviously not practical.

So questions:

1.  Is there a glue that will work without removing the paint on the contact surfaces?  Barring that...

2.  Is there a technique for removing tiny spots of paint to ensure a good glue bond?

[TooOld]

You will get a dozen different ideas so here's mine . I use Detail Tack from Micro Mark , probably the same as Tacky Glue at Michael's . A small dab using a toothpick on your painted surface , let it dry , then place the light or mirror in place . . . done .  Some will worry about it drying out over time but I have models on my shelf 10 years old and the mirrors are still there . If you are concerned apply Tacky Glue to both surfaces  , it works like contact cement and will create a very strong bond but can still be carefully removed if needed . This bottle is 10 years old , it lasts a loooong time .

Edited December 10, 2022 by TooOld

[Ace-Garageguy]

Really, IMHO the best thing to do is pre-fit, drill, and pin any parts that are going to have to be attached to a painted surface...prior to painting.

More effort, but no BS on the back end, as you can use a white PVA glue that won't harm your paint to hold the pins in pre-drilled holes at final assembly.

[PHPaul]

Thanks for the responses so far!

@TooOld  Hmmmm.  Tacky Glue.  I have some of that, I'll give it a try.

@Ace-Garageguy  Yeah, I thought about pinning.  I might try a combination of both:  Pinning the bigger stuff (muffler brackets, luberfiner) and using tacky glue on the smaller stuff.

I'll keep watching this thread and I'll post back with my results.  Be several days I'm sure as I just did the second color and need to wait 2-3 days to be sure the paint has cured before removing the masking.

[Plowboy]

I've glued many many parts without scraping paint off beforehand. Same with chrome parts. I use Model Master Liquid Glue. For body parts with no pins, I use windshield glue.

[StevenGuthmiller]

I use pretty much nothing but clear 2 part epoxy for gluing everything now.

I know, it's more work than other glues, but I don't have to worry about fogging paint, chrome or glass as with super glue, if I apply the glue and let it cure for ten minutes before attaching the parts, I don't have to worry about glue "squeeze out", and once the glue is fully cured, your parts aren't going anywhere.........and I don't scrape paint or chrome off of anything before gluing.

 

 

 

Steve

Edited December 10, 2022 by StevenGuthmiller

[Ace-Garageguy]

Something people tend to forget when gluing anything to any painted surface...whatever you glue to any painted surface will only be adhered as well to the surface as the paint is.

Glue doesn't somehow magically stick to what's under the paint.

It sticks to the paint, period.

So if your paint adhesion isn't the best...

[StevenGuthmiller]

2 hours ago, Ace-Garageguy said:

Something people tend to forget when gluing anything to any painted surface...whatever you glue to any painted surface will only be adhered as well to the surface as the paint is.

Glue doesn't somehow magically stick to what's under the paint.

It sticks to the paint, period.

So if your paint adhesion isn't the best...

True.

But if your paint adhesion isn't good, you're probably heading towards other problems as well.

Masking may not be in your future either.

 

If my paint adheres as well as the 2-part epoxy I'm using, I'm in great shape.

 

 

 

Steve

[Plowboy]

On 12/10/2022 at 11:25 AM, PHPaul said:

Be several days I'm sure as I just did the second color and need to wait 2-3 days to be sure the paint has cured before removing the masking.

Do not leave masking tape on for 2-3 days! That's a recipe for disaster! Especially if the paint you're taping over isn't fully cured. I use lacquer and always remove the tape as soon as I'm done spraying the second color. Always remove masking tape ASAP. 

[PHPaul]

42 minutes ago, Plowboy said:

Do not leave masking tape on for 2-3 days! That's a recipe for disaster! Especially if the paint you're taping over isn't fully cured. I use lacquer and always remove the tape as soon as I'm done spraying the second color. Always remove masking tape ASAP. 

Makes sense, I'll remember that.  I did get away with it this time however.

[peteski]

I extensively use liquid masking media to protect bare plastic gluing areas from paint.  I also use masking tape, andr for small cylindrical shapes I use pieces of stripped wire insulation (basically plastic tubing).

[LL3 Model Worx]

I'd like to add to the great advice above...

I many times have used the original paint color or clear that is on the surface  to adhere small parts.

Like mirrors... say I used an enamel clear coat then I'll take a small amount of that enamel clear and put it on pallet or bottle cap or something and let it tack up then apply to the part and stick it to the model while it's tacky.

Same if it's an enamel or lacquer I haven't cleared... I just take the base color paint and do the same thing.

It will bond fairly decent and it won't leave any noticeable marks.

[tbill]

I’ve been using canopy glue for those particular type items for awhile now ( cab lights/mirrors/air horns/grab handles) it dries clear and if any extra happens to squeeze out from under the part, it cleans off easily with a damp swab.

 

[peteski]

I pin my small items and glue them using CA glue. It works well since the surface inside the hole is bare plastic, and the CA glue will also stay in the hole.

[NOBLNG]

I too try to pin everything, assuming the parts aren’t too tiny….a .020” brass pin is sufficient. Any type of glue that won’t hurt the paint will work then.

[peteski]

Smallest brass wire I used for pinning was 0.012" (and #80 holes).

[Plowboy]

I use .020 styrene rod to pin small parts. Then I hit them from the inside of the body with Tamiya Extra Thin Cement. Sometimes, I'll add a drop of crazy glue to the pin before I cut it off.

[StevenGuthmiller]

11 hours ago, Plowboy said:

I use .020 styrene rod to pin small parts. Then I hit them from the inside of the body with Tamiya Extra Thin Cement. Sometimes, I'll add a drop of crazy glue to the pin before I cut it off.

I also pin with styrene rod and hit the back side with epoxy if possible.

If not, a tiny dab of epoxy in the hole, and the part is not going anywhere.

 

 

 

 

Steve

[customline]

It's drilling ahead of time with a #76, either before or after paint, and pinning with .020 brass and CA for anything I can hold between my time-ravaged fingers. If I've got to hold it with tweezers, then it's too small to drill so the clear lacquer/enamel method or just a pin-point drop of CA works. I cannot keep a #80 drill bit for more than the time it takes to mount it in a pin vise so....anyway, all good methods above; it's just a matter of the situation that determines which one to use. The matter of proper paint prep is the foundation for non-pinned attachments though, total agreement there. CA is good for this but if you fumble with the part and slide it around, you will melt the paint. I have made more than a few messes while "free gluing" with CA on painted surfaces so it must be done (in my case anyway) with extreme focus. CA is very strong and will make an excellent bond but the tiny part should be prepped by removing plating from the mating surface because that bond is pretty weak. That's my $00.02  ?