Glue hood skin to structure - HELP!

[chaos52]

The factory "goop" is gone in a couple places on my hood, causing it to oil-can.

I just tried Valvoline Pliogrip flexible foam. It's one of those 2-part epoxy things. The results were absolutely disastrous. There's only a 30sec working time and it foams up to 10 times in volume. I ended up with most of the tube on the floor and the rest on me. The damn thing cost $37 too.

I read in another thread that Bill440RT used fiberglass filler on one of his cars, but it caused dimples in the hood on a hot day. Can anyone make any suggestions??? I'll just be sitting here trying to scrape foam off my hands, legs, arms and various other body parts.

[bill440rt]

Go to the auto body supply store. Tell them you want door skin intrusion beam foam. It is found on newer cars inside door skins. Keeps the skins from oil-canning on the intrusion beams. 
You could also use seam sealer, but IIRC the original stuff is more foam-like.

Yeah, I remember the fiberglass filler trick. It doesn't expand/contract like the foam would as does the metal.

[chaos52]

Go to the auto body supply store. Tell them you want door skin intrusion beam foam. It is found on newer cars inside door skins. Keeps the skins from oil-canning on the intrusion beams. 
You could also use seam sealer, but IIRC the original stuff is more foam-like.

Yeah, I remember the fiberglass filler trick. It doesn't expand/contract like the foam would as does the metal.

The stuff I used said it was for intrusion beams and rockers....not too wild about trying that again. The bits that did make it on the hood didn't dry hard either - it's about the texture of packing peanuts. When I tried to cut away the excess it leaves a porous surface that would look terrible painted.

The factory stuff is pretty hard. (granted it's 45 years old) Maybe I'll try seam sealer if all else fails.

[Troy]

I figured out that there's low expanding foam and high expanding foam. The high expanding foam goes inside rails and door support beams and probably isn't a great idea for hoods or trunks. I'm gonna fill up my valance corners with it...

Troy

[chaos52]

I called the guy that's painting my car and did a bunch of searching online. Based on what he said and what I found online, I bought SEM 39977 Panel Vibration Control. (Another $55 )

I also was able to borrow the proper gun from the local Auto Value. I'm headed out to the shop to clean up yesterday's mess and try the new stuff. I'll report back with the results.

[chaos52]

The application certainly went better. I will post photos later.

We'll see how it performs after it cures....

[Silver R/T]

You could've also used windshield urethane. Once dries it holds underhood structure and it doesn't expand so it won't swell up and cause problems.

[bill440rt]

You would be faced with a different problem. Paint doesn't stick very well to windshield urethane.

[chaos52]

I hope my mistakes will help future readers of this thread.

Lessons in hood gluing...

1. Do not use foam. Also check the working time on the product. If it's only 30-60 seconds, you're going to have a bad time. It will harden in the mixing tip before you can say "Goodbye $40". The other problem with foam is that you cannot cut away excess without it looking like crap. (you WILL need to with an expansion of 10x)
2. USE THE PROPER APPLICATOR GUN. Seriously, don't try to rig something like I did. The product expands when it mixes together, so it will push back into the cylinders and ruin the entire tube. The applicator guns cost over $100, so try to borrow one from a local body shop, auto body store, friend, etc.

[chaos52]

3. Use SEM 39977. It has a 60 minute working time, doesn't expand rapidly and is thick and viscous, unlike the foam product that has the consistency of water and runs everywhere.

[bill440rt]

Nice work! 
Yep, that's the stuff. I had to get one of those guns, too. Expensive, but if you use them a lot they are invaluable.

[1ol72charger4me]

I was hoping somebody had come up with a technique to solve my loose trunk skin dilemma but I can add a couple of things I've done in the past. For those not wanting to invest in the 2 part gun(which they do make a cheaper one, you just have to ask them to order it) the regular tan body sealer will handle most of the separation issues. To maintain the factory look I just reglue the separated old sealer on whichever side it broke loose on. Usually this is easier than digging out the old stuff. A lot of times it seems that the spacing is just the right width to glue a paint stick in with the sealer and you can tool the edge to hide it. A cool restomod type of upgrade is to caulk all of the seam where the skin touches the inner structure and tool it smooth by spraying some sort of wipedown solvent and using the right size finger. It's time consuming and will probably get you a cut or 2 but will give a nice feel and sound to the panel. Over the years I've noticed that  high end cars (Mercedes, BMW, Jag, Lexus) use a lot of tricks like that to help give a quality feel to whole car. I like to use a urethane 2 part sealer that is non settling or thicker (usually 3m). The work time is short so you can have someone run the gun while you tool or like I do, caulk about 6 inches, tool it then squeeze out the 6 inches of material that are setting up in the nozzle for fresh material and repeat. After you get a rhythm for how long you have , you can do large areas with a single tube. One caution, when changing tubes, dig out all the hard material or gun out till you get perfectly clear new material because even the smallest bit of old sealer will effect the mixing and possibly leave you with a mess of non hardening or semi hard sealer. I keep plenty of torn off shop towels ready to wipe up mistakes or clean  fingers. You can try gloves but your finger has a magic touch of it's own for this kind of work. Insert joke here. Masking tape can help by setting a border line for tooling the sealer up to, giving you a nice clean edge.

[Silver R/T]

You would be faced with a different problem. Paint doesn't stick very well to windshield urethane.

I asked windshield urethane rep and was told it can be painted. Besides being urethane based product (windshield urethane) why wouldn't urethane base/clear not stick to another urethane based product? I have a tube, I guess I need to try it out myself.

[bill440rt]

That's what windshield primer is for. Helps create better adhesion with the urethane to the paint. Otherwise, it wouldn't stick so great. 

[Silver R/T]

There's primerless windshield urethane available now.

[bill440rt]

Ah-hah! Yes, you're right, there is. 
But still, the product chaos52 references above would be my choice over windshield urethane.

[green69rt]

 

[chaos52]

I blocked out the hood yesterday. All oil canning is gone and there weren't any high spots where I applied the product. 

[oldcarnut]

I started another thread on this but then saw this right after using a different search.
I stripped and blasted my hood down to bare metal in prep for paint but noticed the calking/adhesive blob spots have come unstuck in several locations.  While sanding down the hood I noticed there were some dips in the contour that had been leveled out with filler on a previous repaint. If I press open the gap a little more between the brace and skin it will take care of most of it without filler but if I press the skin down on top of the old calking blobs, it gives the dip.  Did these calk blobs shrink over time as well as come unstuck?    Did the windshield stuff work for you?  I already have one of those mixing guns and a bunch of panel bonding where I've been putting in my rear window plug and the hood extension for the bird clone build.  Do you think the panel bond will work for this application with giving problems with heat buckling etc. and would you go by the old glue spot stops or gap it accordingly?

[chaos52]

I stripped and blasted my hood down to bare metal in prep for paint but noticed the calking/adhesive blob spots have come unstuck in several locations.  While sanding down the hood I noticed there were some dips in the contour that had been leveled out with filler on a previous repaint. If I press open the gap a little more between the brace and skin it will take care of most of it without filler but if I press the skin down on top of the old calking blobs, it gives the dip.  Did these calk blobs shrink over time as well as come unstuck?  I started another thread on this but then saw this right after using a different search.  Did the windshield stuff work for you?  I already have one of those mixing guns and a bunch of panel bonding where I've been putting in my rear window plug and the hood extension for the bird clone build.  Do you think the panel bond will work for this application with giving problems with heat buckling etc. and would you go by the old glue spot stops or gap it accordingly?

It has been while...if I remember right the new goop products don't shrink like the original caulk. When I glued my hood I left the metal at a relaxed state (rest the hood on a stand on the inner frame - right side up) and put the goop wherever I thought was necessary. Certainly didn't follow the original blob locations as that would have still left weak spots. I did use bondo filler on the hood to fix low spots where necessary.

I think I'd be more comfortable using bondo filler to fix low spots on relaxed metal than having metal under tension supported by the goop. I'm not sure how heat factors in.

Someone else chime in here to confirm or deny...

[oldcarnut]

I ended up using a product called sikaflex 221.  Time will tell how it works out with hood temps but otherwise did a good job.