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Old 08-12-2008, 04:22 PM
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Bonding fiberglass to steel

I'm just looking for some opinions. I have been cutting a steel hood, grinding the area of attachment with 80 grit, then SPI epoxy primering the area, letting it cure for a day or so, then mixing up 2 part marine epoxy adhesive and applying it to a ground down fiberglass flange 2 to 3" wide and also to the hood. I am setting a woven fiberglass hood scoop with its flange on this area, which is now upside down. I lay some heavy bricks on the part and let it cure this way for 2 days. I then proceed to my bodywork and paint job from there. So far, I have done this twice and first one I did over a year and half ago is holding up just fine. The hood gets plenty of abuse and lots of hot sunshine and sudden rains. I think this method is more than acceptable. I have heard of times when the parts would crack at the seam, or something similar. Has anyone some experience on this type of procedure? or another way to accomplish the same objective..

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Old 08-12-2008, 04:32 PM
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fiberglass and steel don't mix due to the expansion rate diffrences.. if the way your doing works and has held w/o cracking for over a year. it's probably a better way to do it than others, but eventully, it will crack on you
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Old 08-12-2008, 05:07 PM
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I glue fiberglass scoops and other panels( look at the ricer in my photo album) with a two part urethane adhesive from SEM that is for bonding fiberglass to metal. I have never had one crack except in a wreck and that didn't break the bond. It tore the metal. I have a 65 elcamino i just put a glass L-88 scoop on and I have been riding in it for months with no cracks what so ever. and that hood gets slammed often. I do the finish work by sealing the bond area with an epoxy then do the blending body work with dyna-glass and filler to finish it off. Then 2k and sand for paint. Thats how i do it any way, Tim
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Old 08-12-2008, 05:14 PM
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I epoxy straight to the metal, never to the primer, I don't believe the primer is designed to hold anything onto the car except paint. I use the coarsest paper possible, at least 36, sometimes just a grinding wheel then clean the area thoroughly - twice.

Sometimes I use a polyurethane glue like 3M's 5200 this also requires the metal to be prepped in the same way as the epoxy.
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Old 08-12-2008, 09:37 PM
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Fusor has an adhesive designed for mounting fiberglass and plastic to metal that I've used several times with never any failure. Fusor directions stress the use of a quality epoxy primer over the bare steel before applying the adhesive. I think the epoxy primer offers better adhesion, and the adhesive makes up for any expansion rate differences. I use regular fiberglass and filler proceedures to blend the part in after the adhesive cures.

In the old days people tried all sorts of ways to bond fiberglass parts to steel and I never did see any hold up for very long. Epoxy primers and good adhesives designed for the job are the only way to go IMO.
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Old 08-13-2008, 12:08 AM
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I am wondering if - because of the bonding area I have of a min. 2" to around 3", that, that is helping.. a huge fault/expansion or movement would have to occur to break this bond.
I was thinking about using Marintek adhesive for this, but it would be pretty expensive I think. and would you want the adhesive to flex ?? possibly breaking the bodywork bond on top of the hood???
I start the body work using everglass on the topside, not much is used, I keep the filler to a minimum..
on using the epoxy primer before the epoxy resin adhesive, I ways always told to treat the metal first, I could maybe grind a little courser, if that would help.
But again, I didn't experience a failure yet.
maybe the primer is acting as the flex absorber???
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Old 08-13-2008, 06:37 AM
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Just to clarify - when using regular fiberglass (polyester) I agree it does not bond to metal well, it is not an adhesive although sometimes it does work as one. But when using epoxy adhesive - as stated in the OP - it is not necessary to use primer (check the data sheets), epoxy adhesive is designed to stick to metal.

But there are many ways to do this and if using it has worked for you then I wouldn't worry about it.
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