structural adhesive

[Dennis D.]

Doing a r&r on my 70 header reinforcement. Have the bonding strip rivited to the steel bar. Plan to use norton structural adhesive for the bond. Ther are a couple of places where the old adhesive ripped off and left some exposed fiberglass.

Can I use the norton adhesive to fill these few spots?
Or was the underside of the surround gel-coated, and what is the correct way to repair/prep for the install?

Lastly,do the small triangular brackets that bolt the bar ends to the fender wells locate the bar correctly for proper headlight location?

Thanks in advance. Also have a very good used original header bar with a rivited bond strip I can't use. (only has provision for a single vac relay) If anyone needs, I'll sell for what I paid for it. Email me

[Chuck S.]

Re: structural adhesive

...what is the correct way to repair/prep for the install?

Dennis, I have no experience with the Norton adhesive, nor can I say that it's use is appropriate. What I can say is that for any suitable adhesive, the proper prep would be to grind the surface of the fiberglass where the bond is to be made with a coarse grit (36) grinding disc, then air blow and/or wipe the ground area dust-free. The factory sand blasted the fiberglass in the bond areas, but grinding it is more efficient for a small job on the car. If you're having it judged, try to hide the grinding in the bond area as much as possible, because there was no grinding at the factory.

...do the small triangular brackets that bolt the bar ends to the fender wells locate the bar correctly for proper headlight location?

The headlight units are individually adjustable through the bearings and linkage. The height and positioning of the fiberglass surrounding the headlights, and in fact the entire front grille area, is influenced by many more factors than just the small triangular brackets. The triangle bracket hole size in the front bulkhead is too large to provide any precision location from these brackets...I consider them only as reinforcement from the front bulkhead to the nose fiberglass. The long rod brace from the front cross member to the reinforcement angle over the top of the grille opening is what will strongly influence the nose fiberglass height.

[Chuck S.]

P.S.

I recommend you do a preliminary fit-up on the front end, attempting to place the fiberglass in proper alignment to the headlights at about mid-range of the total headlight adjustments. This approach will provide the most room to work for final adjustment of the headlights if minor changes occur during the final fit and bonding. If you can determine the original positons of the all the front end braces, then that is probably the best starting point, but double check the fit-up to see if you can improve it.

Carefully check the complete fit of the hood as well, because movement of the nose fiberglass changes the hood to surround fit. If you need to remove or add hood hinge shims to get the front of the hood level with the fenders, you need to do this before the final fit-up. Check the hood to fender fit, including gaps, all the way back to the cowl...you may find you have to compromise on a best-average fit to the fenders or get into a LOT more work adjusting the inner fenders.

The header bar will pretty much be riding along until the adhesive cures, and then it will be extremely resistant to any large changes in fiberglass position due to the triangle braces to the front bulkhead, so...you want to get it ALL right before you bond.

[Craig S.]

Re: structural adhesive

You might also want to consider LORD adhesive's FUSOR line.......Craig




Lord Corp's FUSOR bonding adhesive line

[Craig S.]

Re: structural adhesive - another link

Here is a link to the FUSOR line of products......Craig




FUSOR Line

[Dennis D.]

Re: P.S.

Great suggestion to mock up a mid point fit. Going to try that. Do you know if the underside was gel-coated, and the best way to repair the few exposed fiberglass spots? Thanks Dennis

[Dennis D.]

Re: structural adhesive - another link

Craig

Thanks for the fusor link. Going to check that out. Dennis

[Chuck S.]

Re: P.S.

Factory fiberglass panels were never gelcoated; the slick surface you see is simply the polyester resin used in making the panel. You WANT to remove that slick surface completely before you attempt to bond anything to the panel. Preparing the surface by grinding with a 36 grit disc will roughen the surface to improve adhesion and remove any loose fibers. Any slight irregularity in the ground surface will be leveled by the adhesive layer.

[Dennis D.]

Re: P.S.

Chuck

The nos bonding strip has a grey factory coating on the fiberglass textured bonding surface. Is this ready to bond or also need to be prepped?

Also the loose fibers look like raw mat in a few spots. If I grind I'll go right through the surround. Thinking of filling them with the structural adhesive. The product claims to be able to do this. Then I'll gring it with 36 grit. Sound right?

[Craig S.]

Re: structural adhesive - another link

Dennis - as I recall, the 127EZ is a good bonding adhesive for attaching fiberglass to metal....Craig

[Chuck S.]

Sounds Like You Are Waist Deep in Alligators...

The nos bonding strip has a grey factory coating on the fiberglass textured bonding surface. Is this ready to bond or also need to be prepped?

Textured?!! Both sides of the bonding strip? The surface of an NOS bonding strip should be almost perfectly smooth unless it has already been prepped by sandblasting. I wouldn't think GM would prep their fiberglass parts before sale. You should be able to SEE the fiberglass strands curling around randomly in the surface, but you can hardly feel them. If the bonding strip is rough on the surface, that almost sounds like hand-laid fiberglass which is neither NOS or GM. I would have to see it and feel it to evaluate the "texture", but to be on the safe side, I would say a little surface grinding to prep would be preferable.

...the loose fibers look like raw mat in a few spots. If I grind I'll go right through the surround.

Fiberglass panels are about 0.080"-0.100" thick. If a couple of passes with 36 grit would put you through the surround, then you have huge chunks torn out. Check the top surface of the surround for any indication of roughness (fibers sticking up) above the torn area. Also shine a flashlight from below and see if you see any light transmitted through...you may have already torn through the surround. It's not hard to do, I've done it myself trying to separate an inner fender from the fender.

If you have already torn through the surround, my approach would probably be to taper grind the torn area and build it up with resin and mat before attempting to bond the header bar, rather than depending on the adhesive to replace the fiberglass. You will probably also have to grind the top surface of the surround and apply resin and mat to the top as well in order to insure a good repair.

Others may be able to offer you better advice on whether the adhesive will be OK to fill the void and repair the top surface. I haven't tried using bonding adhesive to fill holes in the exterior body surface. If it were polyester adhesive, I would have a higher degree of confidence in it working OK since the factory did it that way...all the seams have bonding adhesive finsihed to body contour. In any event, you need the glass fibers in the repair for strength in my opinion.