Effect of Sharpie on glue joints

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Jul 14, 2015
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Northern NJ
Sharpies are incredibly convenient for touching up certain kinds of small finishing blemishes. Sometimes, it is be useful to apply them in or around a glue joint area before gluing takes place. So the question is: does Sharpie adversely affect the strength off glue joints? Is the answer different depending on what kind of glue, or what kind of surface? Some possible combinations would be on wood or paper, with Titebond II, or on other surfaces with epoxy.

Anyone know, or at least want to take a SWAG?
Crazy, off the cuff answer. You know how you can often see Sharpie marks (and even pencil) through paint? If the paint won't effectively adhere to the Sharpie mark, then I would be willing to bet that glue won't, either. No research done.
Hmm, I just actually recently painted a test piece with black Tamiya acrylic over black Sharpie, and it seems to have stuck OK.... I guess I should try contrasting colors so I can see better.

Gonna run a quick test here with the glue.
Not the answer you're looking for but I use Sharpies to touch up chips and scratches on my black rockets as well. However I paint once the rocket is fully assembled. Are you pre-painting the individual components, then assembling?

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I'm building an Accur8 Ragnarok Orbital Interceptor. The dark blue skins are applied to the fins and BT before gluing, then a glue joint area is cut away from the BT skin. Because that area is a tad oversized, and the BT is white underneath, I'd like to (well, I've already done it some, trying to decide if it was a good or bad move) Sharpie around the edges of the glue joint area on the BT so any exposed bits will not show white.

There are a couple of other related bits of construction coming up, all of which boil down to pre-skinned parts being glued, and you can't effectively touch up afterwards without really messing up the skins.
Crazy, off the cuff answer. You know how you can often see Sharpie marks (and even pencil) through paint? If the paint won't effectively adhere to the Sharpie mark, then I would be willing to bet that glue won't, either. No research done.

I thought that seeing sharpie through paint was a result of the paint dissolving the dried ink.

I reckon that as long as the glue adheres through the substrate, you should be good. If the glue is meant to only adhere the surface, first reconsider the meaning of your life, and if the glue ends up bonding to the sharpie, there may be some decrease in strength. As long as the glue penetrates the material or has alcohol level solvents (minimally powerful) (Epoxy probably qualifies) to be able to dissolve the mark and contact the surface, the strength should not be decreased.
I'd put it at slim to none. Even when using a regular white/wood glue. I've never noticed a difference gluing over an ink mark versus bare paper, and I use wood or white glue for most of my rockets, even the J-K capable ones.

Like Tony said, anything with a solvent property will likely dissolve the ink. If you really want to remove it, use a little alcohol.
Some permanent type markers will bleed through all coats of paint applied, even blocker primers. They must be removed with solvent before painting. Though they can "bleed" through various glues, it's more of a "stain" not affecting the bond in typical use.

Paint is not sticking, nope......it's sharpie bleeding through the paint, primer, epoxy, glue..etc.
Something else to keep in mind is that Sharpie ink is used as a resist in some forms of metal etching. If Sharpie ink is resistant to ferric chloride, it probably resists aliphatic/PVA glues also. Mind you I'm no chemist though.
I've been finishing Contest Gliders and rockets for decades with Sharpies of all colors. sometimes over the glues sometimes before the glues. In all cases I've never had a single seperation problem with the glue joints. As a matter of fact Sharpie coloring is the perferred method of adding color and contrast to most NAR contest gliders, helicopters and Altitude models. If it were a problem with glue adhesion I'm sure at some point over the past 40+ years, the practice would not be as pervalent as it is through-out the contest flying community.

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