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JPPadula 10-24-2010 10:06 PM

repairing fiberglass hood
 
2 Attachment(s)
Going to be doing a repair to this 2004 Cobra hood that I will be swapping onto a 2001 GT. I got it reasonably cheap, but it needs some work. For the area pictured, I was thinking of laying glass over the GT's hood to make a mold, and then pulling a part to splice into the damaged hoods leading edge. I'd trim the patch to a smooth edge, trace it to the hood, cut the hood to match the patch and remove damaged area, feather meeting edges of hood and patch glue/duraglas patch in place then lay several laters of matt into the feathered area. Let cure several days to settle in and then grind flat, poly prime and repaint. Not sure if this hood is actually fiberglas or SMC, or what the two materials might do in heat and sun. Since its a hood it'll need to stay flat. Any recomendations?

MARTINSR 10-24-2010 10:57 PM

This is not a detailed explanation but your plans are all wrong in my opinion. What you would do is simply thin this glass down by "grinding" it ,though I wouldn't use a "grinder" I would be using an 8" Orbital sander, much more user friendly.

Anyway, so you thin the glass down to just about nothing. Then you brush it with resin and then lay pieces of resin soaked mat over the area. Sand that just like you would a body filler, shaping it to match the hood. Finish it off with "Fibertech" from Evercoat and there you have it. Once you get the top into shape you turn the hood over and do the same thing on the underside.

Splicing in a section is very difficult in that you are VERY likely to end up with a problem with "ghost lines" after the whole thing is done.

Remember that this hood isn't "fiberglass" but "SMC" and you need special resins and filler (The Fibertech) when working with it.

Brian

JPPadula 10-24-2010 11:17 PM

I understand what you are saying. My fear was looking at the pics, that the glass may be fractured over a fairly large area and that I might get spider cracks. I will try your idea first, I can always cut and spice if it doesnt work out. What "Special" resin should I look for to do the repair. I've seen SMC repair kits at the paint store, but not sure what they contain. When I said grind, I was imagining using a 2" angle grinder with 36grit. What grit are you thinking on the D/A?

MARTINSR 10-24-2010 11:29 PM

Quote:

Originally Posted by JPPadula
I understand what you are saying. My fear was looking at the pics, that the glass may be fractured over a fairly large area and that I might get spider cracks. I will try your idea first, I can always cut and spice if it doesnt work out. What "Special" resin should I look for to do the repair. I've seen SMC repair kits at the paint store, but not sure what they contain. When I said grind, I was imagining using a 2" angle grinder with 36grit. What grit are you thinking on the D/A?

The small angle grinder will work but it is a little hard to control. But yes, that will work. I just like to thin the "glass" more like feathering so your transition from the worked area to the good area is smoother. The resin is simply labeled for SMC.

Brian

JPPadula 10-24-2010 11:40 PM

I went to Evercoats site to check out the fibertech you mentioned and they are showing it as a repair compound that stands alone without matt, Are you suggesting to use it over the SMC resin/matt repair as a filler?

MARTINSR 10-24-2010 11:44 PM

Yes, JUST to level it off and cover up your mat.

Brian

JPPadula 10-24-2010 11:51 PM

Thanks! I'll post when I'm done messing it up...errr repairing it.

JPPadula 11-23-2010 06:39 PM

Ok so I stripped this hood this weekend. 80grit on the DA down to the SMC. As I feared, there are stress cracks in multiple areas. The worst of them I plan on repairing by thinning the SMC in an area around the damage and laying 2 layers of 1.5oz matt using the SMC resin over the surface as a patch, then filling with the recommended fibertech filler.

What is concerning me however is that there were many more stress cracks in the painted surface than show in the SMC now that its stripped. Is it possible that the paint cracked but the SMC surface didnt? Or, might there be invisible microcracks in the SMC that will telegraph back through the paint as it cures? A possible solution that came to me is possibly repairing the broken areas and then laying one continuous layer of 1.5oz matt over the entire hood to hold down any tiny cracks. I've been told that the SMC resin does not wet out the matt well, so I'm concerned that laying a large piece of matt might be impossible with that material (not to metion the 45$ a quart price) Would it be feasable to use standard polyester resin if I'm laminating the whole hood? Input?

MARTINSR 11-23-2010 07:53 PM

Unless someone else comes up with some other ideas if it's cracked it needs to be thinned down (sanded down) and mat and resin put over it to reinforce it.

Brian

milo 11-24-2010 03:31 PM

Use a one to one type Epoxy resin for "adding" or repairs to broken fiber glass or smc, not regular fiberglass building resin.

http://www.a2zautoforums.com/attachm...chmentid=12653
Heres a common fiber repair project where existing material is left in place and the epoxy resin is allowed to "drool" into the fractures..

enjoy-->
http://www.a2zautoforums.com/showthr...6383#post36383

Chris Kemp 11-24-2010 03:47 PM

Fiber glass is great and if used like Brian has stated you will not have a problem. But just like he said, you have to thin down the damaged areas and that means the hairline cracks also. If there was cracks in the paint then the hood is cracked there too. The only way to repair it so it will not come back is to thin down the cracked areas and then fill in those thinned down areas with a repair material. I have had great success using a product called MarineTex. It is a marine epoxy that has been around along time. I have used it from start to finish on the same type of repair that you are doing. It will not shrink or show ghost lines down the road after the sun has baked on it for a while. Not to put down Brian's method because it will work great but IMO MarineTex works on smc better then regular fiber glass.

milo 11-24-2010 04:07 PM

Quote:

Originally Posted by Chris Kemp
It is a marine epoxy that has been around along time. .

good stuff ! :thumbup: the key word is "epoxy resin"

http://www.a2zautoforums.com/attachm...achmentid=9792

JPPadula 11-25-2010 05:17 PM

I would be all for Epoxy resin as long as I knew it would adhere to the SMC. I noticed in the last picture posted that fiberglass cloth was being used. Cloth is necessary when using epoxy because the binder in matt doesnt disolve properly with polyester resin. This leads to another question. I've always heard that you shouldnt use fiberglass cloth under finish coats due to the texture of the cloth printing through after time. Is there a special primer that will hold the texture down? I'm under the impression that polyester primers (what I was planning on using to hold down the repairs) cant be used over epoxy surfaces.

milo 11-25-2010 09:11 PM

Your pictures of your hood are what prompted me to post the link of a project like yours I did in the past with the same smc typ..
http://www.a2zautoforums.com/showthr...6383#post36383 ,

If you do the repair in stages you'll have a easier time being in control, yes shallow the repair area add in some cloth and top/finish with a 2 part putty then your primer will behave

oldBodyman 11-25-2010 10:41 PM

JPPadula,
"This leads to another question. I've always heard that you shouldnt use fiberglass cloth under finish coats due to the texture of the cloth printing through after time. Is there a special primer that will hold the texture down? I'm under the impression that polyester primers (what I was planning on using to hold down the repairs)"

If you go to a boat repair supply house, ask them for a fiberglass cloth/matting called 'veiling', a super fine cloth on one side, a fine matting on the reverse, works perfectly for what you are doing to your hood. It's NOT cheap but the labor savings and finished product more than make-up for the cost.

Get a piece large enough to cover the hood + overhang on 4 sides.

Wet out the hood and place the piece (matting down) starting in the center and work out from there. The dry matting will release any air bubbles thru itself, it's also MUCH cleaner and easier this way

Re-wet the matting from the center out.

Real marine gel-coat works much better than any polyester filler/primer can hope for. Ask for and follow the instructions from the supplier.

Have fun with it.


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