Fiberglassing a fiberglass part to steel

[Biba69]

Hopefully there is a hot-rodder in the crowd who has done this. In my case I'd like to fiberglass in an aftermarket fiberglass hood scoop to the steel hood. In this case the edges are slightly rounded on the scoop.

My (current) plan is to use some chopped glass in the rounded edge area, then a couple of layers of glass cloth. However, since the hood is almost flat I don't see how I can feather it out and have it not have a bulge all around the scoop. I'm not an experienced enough fiberglass person to add a sheet over the entire hood and have it come out smooth.

I'm also a bit worried that over time when the hood is dropped to close it, the edges will start cracking.

Suggestions?

Biba

[Geezer]

If the scoop has a flange all the way around you could mount the scoop from the inside. Then use flush aircraft rivets to hold it in place. That way you would only have a small area to touch up and the rivets should disappear.

[conedriver]

Biba,

Here's a somewhat similar situation. In 2002, I gave my '76 Spider to a friend in Columbus, Ohio for a "generic" inexpensive paint job. He began emailing pictures of progress and, to the dismay of my budget, I saw things that I had not expected. The fiberglass fender flares had been previously screwed on, but Brian explained how these would now be bonded: he told me there is one type of epoxy that adheres best to bare steel, and another that adheres best to fiberglass. He laid a layer of one type epoxy on the bare metal, let this harden, then used the other type to fasten the fender flare to this.

Now that I look at the old picture, I see what must be small screws or rivets holding the flares in place. This was done in 2002, and the result has been flawless; there are no cracks or evidence of screws showing through.

Quote:

Originally Posted by Biba69 Hopefully there is a hot-rodder in the crowd who has done this. In my case I'd like to fiberglass in an aftermarket fiberglass hood scoop to the steel hood. In this case the edges are slightly rounded on the scoop. My (current) plan is to use some chopped glass in the rounded edge area, then a couple of layers of glass cloth. However, since the hood is almost flat I don't see how I can feather it out and have it not have a bulge all around the scoop. I'm not an experienced enough fiberglass person to add a sheet over the entire hood and have it come out smooth. I'm also a bit worried that over time when the hood is dropped to close it, the edges will start cracking. Suggestions? Biba

[k76]

I'm not sure about the adhesion to steel, my background is boats. If we forget about the adhesion issue this is how I'd go about it:
1. Mix up some epoxy and microballons, and make a 5-10mm radius all along the scoop.
2. get some 200g/sqm carbon fibre cloth, 60mm wide and laminate all around. If you use the resin sparingly this will only build 0.3mm, so you could add another layer just for good measure. If you use two layers stagger them to taper the laminate
The reason for using the carbon is that it is way stronger than chopped glass for the thickness
3. Sand down any protrusion and fair in over a decent area
4. Laminate from inside as well, this way you get some mechanical locking

Whatever you do don't use polyester resin, it's glueing properties are hopeless. Roughing up the steel will help adhesion too

[Biba69]

K76, thank you for this very detailed 'how to', along with a list of 'ingredients'. However, would you mind going shopping with me? For starters 60 mm is roughly 2.5" (inches). I pretty much got stuck with the first site I went to: Applied Vehicle Technology I do not understand their numbering, nor would I know if I want plain; twill; UNI; satin. This place sells the epoxy resin in Very Large containers.

This second one is for hobbyists: RC Foam Discount Hobby Supplies - Tapes for Foamies I'm guessing 2" (50 mm) would be wide enough. Is hinge tape what I want? It implies to me it is flexible. 5 yards should be enough but I'd probably get two or three rolls (since they're cheap).

I haven't even started looking for microballons. Primarily aircraft applications seemed to pop up.

The hood scoop is mostly for looks (decorative). However, if I install it on a GTV6 hood (which I think are very ugly), this might give me some additional room up front when I install a Twin Spark in my Alfetta GT. The question would be whether I would cut out underneath the hood scoop to make it functional. If I do it could then be laminated from inside if - I feel the scoop has enough integrity to make up for the missing metal.

Biba

[lowmileage]

Quote:

Originally Posted by Biba69 My (current) plan is to use some chopped glass in the rounded edge area, then a couple of layers of glass cloth.

[Biba69]

I appreciate all posts on the subject, but definitely don't feel k76 is an idiot. In fact, since I can't/won't be able to lay a wide strip around the hood scoop - because it would look horrible - I need strength with just a narrow band. This is not remotely like fiberglassing in fender flares since you have a lip on them, can poprivet (or?) the edge to hold in place, and can then fairly easily feather it out. In this case the edge rounds Under, so most likely it will be just a thin narrow strip of (?) holding it to the steel hood.

Biba

[k76]

Quote:

Originally Posted by lowmileage Don't use fiberglass cloth - use Matte. Cloth isn't as strong and the weave pattern will come thru the paint. Saturate the matte fully with fiberglass resin. Fiberglass cloth Vs mat - Corvette Forum Ignor post # 5 - guy is an idiot who doesn't know what he's talking about. As far as chopped fiberglass, there use to be a product called "Tiger Hair" which you might want to look into.

[lowmileage]

Quote:

Originally Posted by k76 Hi lowmileage, Biba was actually poster #5, but I take it you meant to insult me?

[k76]

Biba,

Sorry for working in metrics, but 200g/sqm is about 7oz/yard. It can sometimes be hard to find this stuff as Boeing and Airbus are very fond of it. Satin is a very fine weave and twill is a course weave. Plain is somewhere in the middle. I wouldn't be too concerned with what you get, satin is the best but also more expensive. If you can get tapes that's nice and easy, but you could cut it yourself too.

If there are any composite shops in your area I recommend going there. They will cut just the length you need, and have various sizes of epoxy etc. Model shops might be good too. Some people will charge you silly prices for a little bit of carbon. If you can't get a decent price I probably wouldn't bother, fibreglass probably will be ok

[k76]

Quote:

Originally Posted by lowmileage NO NO NO - A THOUSAND TIMES NO - I was talking about the #5 post in the link I provided from the Corvette Forum. You know I wouldn't have said anything like that to you. I apolige for the misunderstanding and I will now correct my post.