Fixing fiberglass screwups?

I fiberglassed a bunch of shrouds on a Cosmodrome Vostok, I extended the fibreglass past the shroud onto the tube to give them more strength (ie: that wasn't the screwup ). I used a random orbit sander to sand down some of the imperfections and in a few spots along the shoulder between the shroud and tube I sanded through the epoxy and exposed the glass cloth.

Question 1) Have I screwed myself? Do I need to re-fiberglass the whole shroud now? The fiberglass was added to protect the paper shrouds, it's not really meant to be structural so I'm hoping I can just fill the glass with CA or something...

Question 2) What should I use to fill the divots/pin holes in the epoxy? I see a lot of talk about 'spot putty', are there some that're better than others? I used West Systems epoxy to lay up the cloth, are there certain putties I should be using with that?

Thanks!

Fiberglass is like working with metal, it can almost always be fixed. Post some pictures if you can. From the sound of it, what I would do is tape off the exposed area (doesnt sound too deep) lay down some resin to cover exposed surface (enough to overlap mask a bit) and pull masking before it sets. Then the filling and sanding starts. I'd use Bondo spot putty with a 360 grit paper. If I'm going for a killer finish, I'll sand, primer, fill, sand, prime as much as four times before final prime.

I dont think there is a right or wrong way but I personally wouldn't coat with CA. Hopefully someone with more experience will chime in.

even if you completely sanded through the glass, if it's not structural some clear resin or even a little bit of CA that's nice and smoothed will work great to keep the paper good. and if the glass was properly wetted before you left it, the glass is still impregnated and the paper is still good.

but like the above poster said, if you're going for a good finish, it's a little more work

Damage is illustrated below, I've got a couple of small spots like that. I think I was a) a bit skimpy with epoxy when wetting out the cloth b) used a bit too light of cloth so it didn't absorb much epoxy rendering the final cured result fairly thin. I used 2 layers of 0.75oz cloth thinking it'd keep the weight down - I wasn't using it for structure, I just wanted to protect the paper shrouds from my clumsiness during transport.

The spots are fairly small, could I just use the spot putty to cover it up or should I epoxy it first? I don't have the 'glazing putty' stuff that comes in the tube and you apply directly, I have the 2-part stuff similar to epoxy that you have to mix up first before spreading on.

The astute reader will note that my Vostok shrouds are black as opposed to the white poster board that by default comes with the kit. I screwed up one of mine and had to find replacement paper, for whatever reason the nearby Staples didn't have white...

hmm, i would say anything nonporus that doesn't leave small bubbles, so a good filler putty could easily do the trick, or epoxy if you think the glass might be porous. if you're gonna use putty you should rough up the spot a little, too fine a grit will make it hard for the putty to stick, other than that, it should be a pretty quick fix.

if you don't want to put on the gloves and do a whole ordeal, there's no need to

Can you still make this the part that goes up against the core BT? If so, there's no need to patch it up at all.

That small spot is a non-issue. If it were a high-performance rocket, it might be, but that doesn't exactly describe the Vostok.

Don't sweat it.

-Kevin

cosmodrome said:

Can you still make this the part that goes up against the core BT? If so, there's no need to patch it up at all.

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See, now that's the kind of advice I was hoping for. (No disrespect to those that posted helpful replies, I'm just really lazy). That's exactly where the hol occurred: where the seam on the shroud meets the lower tube. If you look carefully in the photo you can kinda see the seam running up and to the left, you can also see the bow in the shroud where I squeezed a bit too hard when waiting for the glue to set when attaching it... Getting a good looking Vostok is proving to be challenging for my meagre skills.

troj said:

That small spot is a non-issue. If it were a high-performance rocket, it might be, but that doesn't exactly describe the Vostok.

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*heh* Yeah, I won't be setting any altitude records with it. So I take it on a high/fast flier the issue with a hole in the fibreglass is that it a) creates a weak spot in the tube potentially leading to tube failure b) could maybe delaminate the rest of the epoxy at high speeds?

Spurkey said:

See, now that's the kind of advice I was hoping for.

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Glad I could help.

Spurkey said:

*heh* Yeah, I won't be setting any altitude records with it.

Click to expand...

Maybe a 'lack of altitude' record?

Spurkey said:

So I take it on a high/fast flier the issue with a hole in the fibreglass is that it a) creates a weak spot in the tube potentially leading to tube failure b) could maybe delaminate the rest of the epoxy at high speeds?

Click to expand...

'tis indeed a weak spot. For high performance, yeah, it might create an issue. But for something like the Vostok? It's an annoyance, nothing more, and the idea of hiding it is perfect!

-Kevin

If it wont be seen, who cares. If it's visible, fix it. Otherwise spend your time on something else.

Experience tells me you should use resin after sanding the surrounding area and blend as best you can. Let dry, lightly sand (scratch it up) with 120 or 80 grit so the resin gets a good bite. Go to you local auto supply store and get polyester putty. Works like plastic body filler only it's creamer, smoother, fills pin holes better, easy to sand down to 220 grit. I always glaze coated my plastic work with it to fill deep scratches and pin holes. It's catalylized so there will be no shrinkage as long as you you don't dump primer on it and give it ample flash time between sanding and additional coats of primer. Laquer will soak in and sometime shrink later on as laquer thinner will actually soak in the filler and make it swell, then long term flash will shrink. I'd use enamel prime if possible or epoxy primer or a catylized primer.
I've fixed many a glass hull boats and Vets and SMC panels.
If you are like me, it's a showing of who you are and what you can do so mistakes that show isn't what you want. But mistakes can always be corrected and will never show if done right.
Woody