How To: Preparing G12 (Filament wound) air-frame for primer?

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jahall4

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I have performed a cursory search for a thread specific to the title and found nothing. So I thought I’d start one. Frankly I’m sort of surprised so if I have overlooked one my apologies.

So here’s the specifics… after you have cleaned the parts maybe even used alcohol as the final step to remove absolutely all traces of greases and oils…

… is it beneficial to sand? If so what grit or progression of grits?... and why?

The assumption is that any filling and shaping was done prior to this step of primer preparation. For instance on a defect-free tube or nosecone there may be nothing to fill or sand.

Thanks in advance for your recommendations!
 

rms

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I prime with automotive high build primer after sanding the fibreglass parts with 120 or and 180 and then 220 grit. Once primed I sand the primer with 220 and then 320 and then paint. Why that way? That is the way I have painted cars. I have never seen the need to go to 400 grit or finer. I do use two stage paint though and sanding scratches aren't a problem. I don't wet sand just because I don't like the liquid mess it makes but in saying that I have wet sanded the clear coat with 600 to 1500 or 2000 and polished to take out orange peel. Clear is a lot cleaner when wet sanding or I just don't see the mess:) I have not seen a fibreglass tube that is so perfect that the primer doesn't fill something, be it pin holes or cloth weave. In my thinking primer is cheap insurance in getting a good base for the topcoat.

Greg
 

dhbarr

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I've read this thread more than once, but I don't recall it providing any info about painting. Does it? It's a log thread, where?
Apologies, misheard a general fiberglass prep query, not a paint-specific one.
 

mikec

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I've always just used one coat of regular primer, no sanding or maybe a light dry sanding with 400 grit, and called it good. I've never had what I felt was a significant defect on a G12 tube.

I'm sure you'll see a whole spectrum of painting level of effort being discussed. Do what makes you happy.
 

mpitfield

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I like to use about a 100 - 120 grit on the clean fiberglass, the lay down a couple of light Dupli-color filler prime coats then inspect for imperfections, fill imperfections with 3M spot putty sand with a 220, repeat until tube is defect free. If defect free from then start then move onto the paint, although on glass I typically wet sand with 400 before starting my base coats, or on paper tubes I use 320 dry.
 

OverTheTop

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My fiberglass birds always start with a wash as per the suggestion in that bonding thread (although in my case I choose MIBK as the solvent). That gets rid of any mold-release compound. I then build the rocket, and when ready to paint it gets a light sand with 220 grit. Then I use a plastic primer before application of the rattle-can paint. I generally stick to more reputable brands like 3M and Dulux.

If they go in for the automotive two-pack treatment with my friend I have no idea what the prep is (but the results are great :)).
 

jahall4

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Apologies, misheard a general fiberglass prep query, not a paint-specific one.
No worries always a good read and not surprising the folks are using around 220 for paint, much like is recommend for epoxy bonding in that thread.
 

jahall4

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So what I’m gleaning is the most use between 220 – 400 grit before laying down a primer.

Also a few of you have mentioned a filler primer like Dupli-color which is a go to product for me.

Anyone not sand G12 at all or something else very different?
 

mikec

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Anyone not sand G12 at all or something else very different?
I've never sanded it at all before primer, but like I said above, there are wildly varying levels of painting effort and no "right way" IMHO.

If there's nothing to fill you don't need a filler primer, but it can't hurt if you like it. Duplicolor doesn't fill much anyway in my experience.

Keep in mind that filament-wound tube is a far different beast than laminated fiberglass over a substrate. The old G10 tubes were even better than filament-wound but alas, nobody seems to be making them any more.
 

caveduck

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After a solvent wash to kill the mold release I go straight to Klass Kote epoxy primer, which is pretty high build, sandable in a few hours, and has amazing sanding properties (practically will not load up the sandpaper). Sand with 320 - either wet or dry - and you're good to go.
 

jahall4

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After a solvent wash to kill the mold release I go straight to Klass Kote epoxy primer, which is pretty high build, sandable in a few hours, and has amazing sanding properties (practically will not load up the sandpaper). Sand with 320 - either wet or dry - and you're good to go.
Interesting... Do you spray or apply with a brush?
 
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