First Fiberglassing Questions...

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Well-Known Member
Dec 30, 2003
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I hate to make another thread about fiberglassing, but I need some answers.

I am probably going to get a Cosmodrome Black Brandt , and I decided this will be my first fiberglass rocket. I do not have many resources here (Walmart.....) I need to know a few things:

1. Can I use Devcon (viscous) 30 Minute Epoxy instead of ordering a somewhat large/expensive epoxy, such as west systems or aeropoxy laminating?

2. Could I use bondo (Or whatever is the brand that Walmart carries...Ill check it out soon) on this kit? Would I need a lighter oz glass?

3. Do I need to put a thin layer of epoxy under the glass, then a thicker layer over so that it soaks in the glass?

4. (correct me if im wrong) You are not supposed to sand fiberglass, just use filler/primer to fill in the weave (according to shadow composites, I think) right?

Ill probably have more questions later on, but thanks in advance!
I can't really answer your questions point by point but I can tell you what I'm doing to save some money on my fiberglassing job.

I'm using a $7 can of polyester marine resin in most areas.
It has a strong long lasting odor so it can't be used inside the house. It's not as flexable as epoxy so in fin joints I'm using 90 minute epoxy. I'm going to put a thin coat of Bondo filler over the whole thing to get a smooth finish. Total cost to me is $7 since I allready had the cloth, the 90 minute epoxy and the Bondo.

Please do yourself a really big favor.

Save the polyester resin for your boat! Then sell the boat!

Don't try to save money that way, you will regret it. Honestly.

There is absolutely no comparison between polyester resin and epoxy resin. They are not even close.


It's working great actually. Hercules couldn't pull it off and if he did it would take wood and phenolic with it. That being said though I do use epoxy in high stress areas just to be sure. I also use epoxy if I'm glassing to G10.

OK, if it works for you.

I can't argue with success


As far as which epoxies to use, a thinner epoxy such as West Systems or Hoby Poxy Finishing resin is highly recommended. The big disadvantage of Polyester resins is the is strong and unsafe...use of this resin requires a well ventilated area. I used to use Polyester resins in the past...many years ago, but with Epoxy resins being odor safe and stronger than polyester on the whole, they are the way to go. A glassing resin kit with Epoxy Resin and hardener will cost about $12 at the hobby shop.

I have not used Bondo filler, but I have user Evercoat Formula 27 General Purpose Filler for boats and it works well. I would imagine Bondo would also do fine.

I put resin all over the bodytube fairly thick, then pay ther cloth over top. It will absorb the resin and "wet out" by itself. A squegee will force the excess resin up through the weaves and out from under the cloth and some resin is used on top of the cloth to keep your squegee "lubricated" while in use. Resin first guarantees the cloth will adhere to the bodytube.

As far as sanding goes, you can lightly sand the cloth to remove some of the dried resin, but in general you are correct, sanding too heavily can cut into the cloth. In this case, you can just hit it with some resin, let it dry and re-sand. For heavier cloths, 6oz and above, many will glass with the cloth, then lay another wrap of 1.5-2oz cloth over top. The finer weave cloth requires less sanding and filling.

Good luck :),

When fiberglassing, should I overlap the cloth or leave it flush?
I overlap and then sand the overlap down to flush with the original layer. If you can get it flush, go for it, but I've personally never been able to get in the ballpark the way the weave shifts on glass.

Try this link below and see if the pics help; it's how I glass and you should have pretty good luck with it if you try.

<a href="">Glassing Bodytubes</a>

Thanks!! That link helped out a bunch. After about 5 glassing attempts, I think I got the basic technique down. Now for another question:

If I made the cosmodrome black brandt, would I want to glass the body tube before everythink is assembled? How would I cut out the fin slots again?

Glassing fins: is there any special technique to this? Do you just lay glass out on a epoxy coated fin? Note: I know I probably dont need the fins to be glassed, but this is going to be my glass experiment kit before I try my hands at a LOC V2 4" (although if it becomes a problem, I might get a glass sock from giant leap for the body tube).