Using Something Other Than Silicone

[jbs72697]

I’m getting sort of close to beginning the early stages of my 818, which means doing the floor pan panels. The manual says to use silicone adhesive along with the rivets. Silicone makes a good sealant, but it’s not the greatest adhesive. I’m considering using a two-part epoxy adhesive (Pro-Set) which should also add some strength to the bonds. Is that something that might work, or is it not recommended?
Thanks

[edwardb]

Silicone plus the recommended rivet spacing results in a very strong bond. It's very difficult to take back apart without serious damage to the panel. I know from experience. Thousands have been built exactly that way.

If you're really determined to use something else, polyurethane is another choice. I tried it and didn't particularly like it and found it harder to clean up. But something to consider. Breeze sells Bostik. https://www.breezeautomotive.com/shop/bostik-1100-urethane-adhesive-sealant-black/. Sikaflex-221 is another choice.

I personally wouldn't use 2-part epoxy.

[narly1]

Has anybody considered or tried 3M VHB tape?

It's routinely used in utility trailer construction to bond sheet aluminum exterior panels to the steel frames of enclosed utility trailers.

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

[FF33rod]

As I understand it, the silicone is recommended more to eliminate rattles than to provide structural strength. I doubt that any of the aluminum panels in any of the kits are a structural part.

Steve

[JohnK]

Lots of folks have asked this question, myself included. The overwhelming guidance is to use what's known to work, i.e., silicone. It's inexpensive, easy to find, easy to clean up if it squeezes out, and it works. I powder coated my panels a metallic silver, so I splurged and went with the GE Metal Silicone II (https://gesealants.com/products/metal-silicone-2-sealant/).


Has anybody considered or tried 3M VHB tape?

It's routinely used in utility trailer construction to bond sheet aluminum exterior panels to the steel frames of enclosed utility trailers.

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

I'm a fan of 3M VHB for other uses, but I think it's too thick to use to join sheetmetal panels in this case. I think it would create problems with gaps between panels that are otherwise supposed to be laying flat on top of each other. Tolerance stacking problems with sheetmetal fitment can become a real PITA.

[J R Jones]

jbs, I recently bought an unfinished 818 to modify for an alternative body. I questioned the assembly manual direction to use silicone. 100% silicone with the acrid smell has better bond strength than the sensor safe blend.

None the less, body shops and assembly lines use methacrylate or an epoxy. Methacrylate is better for metal. They are especially good with different materials.
Ashland Panel Bonder, 3M and Plio Grip, but you will never get the panels off without ruining them.
I had to remove some of my aluminum panels and the silicone sticks better to the aluminum than the powder coated steel, but they peeled off with a putty knife.
The body shop panel bonding kits (220ML) is cheaper than the smaller epoxy (50ml) kit, like Loctite EA 9460.
I don't use polyester resin anymore. Epoxy has better physical properties, but more expensive.

[edwardb]

As I understand it, the silicone is recommended more to eliminate rattles than to provide structural strength. I doubt that any of the aluminum panels in any of the kits are a structural part.

Steve

FWIW, I made a similar statement several years ago in a thread (e.g. aluminum panels aren't structural) and was quickly corrected by a number of experienced builders whom I believe and respect. I'm not an engineer so can't provide any data or proof. But apparently they do provide some measure of added strength and/or stiffness.

Panels properly installed with the minimum recommended number of rivets (2" spacing on panels only, 3" spacing into frame members) aren't going to rattle. I'm surprised how many times this comes up and people think that. Adding silicone or another adhesive (e.g. polyurethane) adds more strength and seals the joint. I've mainly used plain GE Silicone 2 from Home Depot and the couple times I've had to take something back apart, I had to be very careful to not ruin the panel. As I mentioned before. More exotic materials don't hurt anything. But in my experience not necessary.

[ggunter]

As others have said silicone is a great bond and the panel adhesives are also good. The marine industry uses 3M 5200 as a sealant and bonding agent. After that stuff has set you can pretty much take the fasteners back out and it will stay there forever. It has the texture when cured, of a stiffer silicone. For disassembly I would slide a piece of piano wire under the panel and cut the seal by pulling the wire with two handles, almost like a garrotte.

[narly1]

...I've mainly used plain GE Silicone 2 from Home Depot and the couple times I've had to take something back apart, I had to be very careful to not ruin the panel.

I haven't used it on a FFR car, but I do know that if you can get a piece of string in between two parts bonded with silicone you can use it like a wire saw to cut through the stuff.

The string technique also works for removing double-sided tape and adhesive backed velcro.

[FF33rod]

FWIW, I made a similar statement several years ago in a thread (e.g. aluminum panels aren't structural) and was quickly corrected by a number of experienced builders whom I believe and respect. I'm not an engineer so can't provide any data or proof. But apparently they do provide some measure of added strength and/or stiffness.

Panels properly installed with the minimum recommended number of rivets (2" spacing on panels only, 3" spacing into frame members) aren't going to rattle. I'm surprised how many times this comes up and people think that. Adding silicone or another adhesive (e.g. polyurethane) adds more strength and seals the joint. I've mainly used plain GE Silicone 2 from Home Depot and the couple times I've had to take something back apart, I had to be very careful to not ruin the panel. As I mentioned before. More exotic materials don't hurt anything. But in my experience not necessary.

I stand corrected, thanks Paul

Steve

[jbs72697]

Thanks for all the feedback everyone. I am in the boat business so I’m pretty familiar with a good variety of sealants, adhesives, caulking (3m, Boatlife, Sika, Pettit, West System, Pro-Set). That’s why I questioned silicone. Any silicone I see is only labeled as a sealant. It’s just not a great adhesive. That being said, the fact that thousands of cars have been put together using it and the advice here I may just go ahead and use silicone especially if down the road I need to take something apart. It would certainly be easier