Aluminum panel bonding

[rtbellah]

Has anyone ever tried using 3m panel bond adhesive in place of silicone for panel bonding/sealing. It is used extensively in the autobody repair industry and would be much stronger than silicone. It seems to me that we should be using the strongest adhesive available...any thoughts?

[egchewy79]

rivets will be doing most of the work. i suspect that the 3M is much more expensive than your average GE silicone.

[cob427sc]

The other issue to remember is a lot of us, for various reasons, at some time in the future or even during the build need to remove a panel. It's not easy getting one off that has been silicon glued without bending/damaging the panel. Not sure you could save a panel using that material.

[JohnK]

I know it's tempting to look at the recommendation to use silicone and think... "pffft, there's way better stuff out than that!" I know, I've thought the same thing and asked the same question before installing my panels. This actually gets asked with some regularity. The overwhelming consensus by those that have built many, many of these things is that silicone works, is cheap and easy to find, and is plenty strong enough. That said, there are folks that have used other products and those work too. Do you need extra strength beyond what you get with silicone? I have no idea, but my guess is probably not. In the end, do what you're comfortable with. No real wrong answers here (unless you need to remove a panel down the road).

[J R Jones]

RT, absolutely stronger and not removable without damage. I build combinations of disparate parts into project cars. 3M and Pliogrip panel bonder is tough and long lasting.
One of the toughest materials to bond-to is cross-linked polymer (CLP) injection moulded parts. I had to make a Lexus ECU mount box molded in CLP fit a street rod. The OEM mounts were removed and threaded mount blocks were fabricated. Bonding them was required. To select a bond agent I set-up an experiment. I cut one inch lengths of one inch aluminum angle. I bonded them to the back side of the CLP box. After four days I broke them off.
Urethane silicone, structural cyanoacrylate and Pliogrip broke off with increasing difficulty. The Pliogrip was so effective it pulled out a chunk of the box material.

I build bodies from raw materials, sheets, tubes and angles, bent and cut to fit fixtures. I started bonding with epoxy resins and adhesives, and added panel bonder. The thickness and working time make it easy to work with. I have used glass cloth in Pliogrip for additional strength. It is like chemical welding.
jim

[Avalanche325]

.....because of all the roaders out there that the panels are falling off of?

Most of the silicone is for waterproofing. Rivets hold the panels on.

[Avalanche325]

I should add..... Just joking around. There is nothing wrong with thinking about better ways to do things.

[NAZ]

I've used 3M Panel Bond and found it to be great at bonding non-structural panels PERMANENTLY. But you you ever want to separate those panels in the future -- good luck with that.

[edwardb]

I posted this in my truck build thread... I've normally used silicone for my builds. GE Silicone 2 from my local Home Depot at around $7.00 per tube. It's plenty strong enough. As already stated, the bonding is a combination of the adhesive and rivets. Done with the proper amount of adhesive and recommend rivet spacing, the strength is more than adequate. It will come apart if you have to, but even with silicone you have to be careful as the parts will get distorted getting them apart. Sometimes to destruction. Sometimes not. I've experienced both. My main complaint about the silicone RTV products is they're a pain to clean up excess and squeeze out. I've found plain old isopropyl alcohol or Goo Gone Gel work OK and about the same. Haven't found anything better. If you wait too long and it skins over (happens pretty quickly) gets a little harder. On one build I tried Sikaflex 221 polyurethane adhesive. Didn't really like it. Granted I'm sure it's stronger. To the point where panels are probably permanent. But I found it thick and messy to use and also not particularly easy to clean up.

For my truck, there are 1" sheets of insulation foam between an upper and lower floor. Also used on the hot rod. The Factory Five instructions said to use 3M 5200 Marine Sealant White to glue it in. Although it's apparently been around for years, first time I've heard of it or used it. Turns out it's a stock item also at Home Depot. A little more pricey than RTV at about $18 a tube. But still much cheaper than some other exotic materials. After using it, I may try it on the next build (if there is one...) for regular panel bonding. It has a nice consistency, sets up much slower so lots of working time, and cleans up instantly with a wipe of a rag with mineral spirits. It's a polyurethane product and very strong. I had a couple spots to clean up after it cured and the bond was very strong. This too would be an absolute permanent attachment. But something to consider if you really want to go that way.

[jts359]

I have been using 3m 5200 for years on marine use , That said if you have any plans of taking anything apart dont use it , Its that strong , Ed

[Lidodrip]

I have been using 3m 5200 for years on marine use , That said if you have any plans of taking anything apart dont use it , Its that strong , Ed

Completely agree with Ed - some large catamarans will use 3m 5200 to bond the keels to the hull. Strong enough to keep the keel on, but in the event of a grounding or strike of a submerged object it will shear off, leaving the hull intact. If you want something that is similar to 5200, but with the potential ability to separate later down the road, consider using 3M 4200.

[Rdone585]

I used silicone primarily so the aluminum panels would not rattle years later. Good news is that worked. I've ridden in some that didn't use silicone and they didn't feel as solidly built. Perhaps everyone now does it, and some also use the dynamat (or a cloan) product to give the car a solid feel.

[J R Jones]

There are two priorities in this thread, ultimate bond strength and potentially removable. With both in mind I will point out not all silicones are the same. Original 100% silicone with the sharp odor (acidic acid) has the strongest bonding. It is also corrosive in electrical environments. Alternative silicones are available known as "sensor safe" electrical grade , it is slightly more gray in color and does not have the sharp odor. The third silicone is multi purpose, similar to electrical grade.
I did development of a jet watercraft and had to seal the pump to the bottom of the hull. I originally used 100% silicone but the service guys could not remove the pump, prying it out removed some gel coat and fiberglass. I switched to the electrical grade silicone and everyone was satisfied. I retained adequate sealing and the reduced bond strength was serviceable.
jim

[frankeeski]

If you decide to use silicone, don't buy large sized tubes. Buy the smaller, toothpaste sized tubes. If you don't seal the end of the large tubes they turn into a hassle un-clogging the end. And if you use the smaller tubes, you're less likely to over-apply the silicone. You'll thank me later.

https://www.youtube.com/watch?v=qyXOKHhONxY

[rtbellah]

If you decide to use silicone, don't buy large sized tubes. Buy the smaller, toothpaste sized tubes. If you don't seal the end of the large tubes they turn into a hassle un-clogging the end. And if you use the smaller tubes, you're less likely to over-apply the silicone. You'll thank me later.

https://www.youtube.com/watch?v=qyXOKHhONxY

Thanks for the tip...at least in the tight spots it will make life much easier!

[Andrew Davis]

I agree that smaller tubes of silicone would be helpful or less wasteful.
Considering their use, I believe the design intent is for sealing cockpit area against fumes, noise, moisture and vibration. Especially as none of the aluminum panels appear to be structurally significant. I may be 180 out on this, wouldn't be the first time.

[edwardb]

I agree that smaller tubes of silicone would be helpful or less wasteful.
Considering their use, I believe the design intent is for sealing cockpit area against fumes, noise, moisture and vibration. Especially as none of the aluminum panels appear to be structurally significant. I may be 180 out on this, wouldn't be the first time.

I made this statement some years ago not long after I joined the forum, e.g. the panels weren't structural. Was challenged by a bunch of forum members. They apparently do add some stiffness to the chassis. Look up "stressed skin."

[J R Jones]

I made this statement some years ago not long after I joined the forum, e.g. the panels weren't structural. Was challenged by a bunch of forum members. They apparently do add some stiffness to the chassis. Look up "stressed skin."

Yes, ultimately one cannot add material to an open steel tube structure without improving the physical characteristics. 0.035 aluminum and pop rivet's is not much structure and in an instrumented analysis the incremental improvement would be small.
Empirically, I expect one could not "feel" a difference.

The Tool Baron's video demonstrates using a foil sheet to fill a fillet joint; that is not even 0.035 structural, but it brings to mind my experience last night. I have an old Ferrari Dino body going on an "eight one eight" chassis and the vintage bonding of FRP panels is crappy. The door frame delaminated at the upper edge and along the hinge jamb where outer and inner panels meet. I ground away the crap and got out the Pliogrip panel bonder,
I often squirt-out an appropriate blob and mix with a putty knife for small tasks. This was a big job and getting the bonder into deep narrow fillets justified a mixer nozzle. I layed-down beads in the door jambs and challenged self-poisoning by licking my finger and shaping the bead into the fillet. It looks marvelous, and does not taste half bad.
The upper frame is an almost blind cavity and access with an 18 inch gun difficult. I pried open the cracks from the outside, squirted out a bead and worked it in with my finger. Moving to the inside of the joint I could deposit blobs of bonder but not as deep as they need to be. I spied my air hose/gun on the floor.... I blew the wet bonder into the joint which also spread and smoothed the bead. I was amazed. This morning the spring clamps came off and all is well.
jim

[edwardb]

Yes, ultimately one cannot add material to an open steel tube structure without improving the physical characteristics. 0.035 aluminum and pop rivet's is not much structure and in an instrumented analysis the incremental improvement would be small...

For the record, the majority of the aluminum panels Factory Five uses are 0.040 inch. I've seen thicker. Like the firewall on the truck I'm building right now and I assume the hot rod is the same. But never thinner.

[NAZ]

Jim, using compressed air to move the bonding agent where you need it is a clever idea. I'll have to keep that in the memory bank for some future need.

[J R Jones]

For the record, the majority of the aluminum panels Factory Five uses are 0.040 inch. I've seen thicker. Like the firewall on the truck I'm building right now and I assume the hot rod is the same. But never thinner.

Fine point for the record. On the occasion of fabricating inner panels for the rear fender wells, I searched out the original 818 parts. I have a shed full of unused FFR parts and my measurement was casual, ignoring the Kaiser .040 printed for all to see. Actually my old Mitutoyo now says 0.038.
On the topic of adding structure to the chassis, my Dino body is a hand laid cloth monocoque, end to end. This was necessitated by the flimsy VW bug pan that lived there previously. The major beam structure is in the rocker panels. The roof trusses and wheel wells also contribute to body stiffness, I reworked the (818) rear spring tower crossmember to pick-up the inner well well surface to stabilize the upper body. The .040 aluminum panels were not going to do it. I fabricated new panels from pre-formed epoxy cloth sheet, 0.100 in this case. I achieved the structure I was seeking and more. I also tie the door hinge jambs into the steel structure at the front of the cockpit. I obsess over structure, and have never made anything but cosmetic parts from .040 aluminum.
jim

[valvestud]

Acetone readily removes uncured silicone.

[narly1]

Has anybody done a build using VHB tape instead of silicone to fix/seal the aluminum panels to the frame?

You'd still need to use silicone for panel to panel corner joints though....

https://www.3m.com/3M/en_US/vhb-tapes-us/applications/transportation/

[edwardb]

Acetone readily removes uncured silicone.

OK for plain aluminum. Acetone doesn't play nice with most powder coats or paint if you've gone that way.

[JohnK]

Jeff Miller shared this about cleaning up silicone caulk that squeezes out of a joint in a thread I started a while back, and it was a wonderful bit of advice. It made cleaning up joints when bonding the panels a breeze:

"when you get a little excess squeezing out that you want to remove... spray it with Windex before you scrape. The Windex wets the area around the bead and causes a skin on the silicone so that it scrapes off cleaner. Also spray it on the scraper you are using. Every time you clean it, spray it again. It's a trick I used when I had my auto glass shop for cleaning up seallants...daBat"

[rtbellah]

Has anybody done a build using VHB tape instead of silicone to fix/seal the aluminum panels to the frame?

You'd still need to use silicone for panel to panel corner joints though....

https://www.3m.com/3M/en_US/vhb-tapes-us/applications/transportation/

THAT is an interesting question...I hope someone has used it and replies as to the effectiveness...VHB would be less of a mess and wouldn't end up all over every surface within 10 feet like silicone tends to. I would be more concerned about the ability to adjust panel positions as you assemble - once you stick it - it is stuck! Curious why you think panel to panel would still require silicone? For me silicone is like working with Henry's asphalt cold roofing compound - no matter how careful I am I still get it all over unintended surfaces. :D

[narly1]

Curious why you think panel to panel would still require silicone?

Sorry I should have been more explicit: I meant sealing a right(ish) angle vs lap joint where there is no surface to surface interface between the two panels. Envision the thin edge of one panel butting up against the flat surface of another...

And I agree with your "you only get one shot at placement" sentiment...I hadn't considered that.

Earl