Adhesive/Sealant Instead of Silicone

[Blwalker105]

Anyone out there using alternatives to silicone for aluminum panel installation? I am looking toward strengthening the rivet bonding juncture instead of just waterproofing it. My neighbor is a race car fabricator and likes Loctite Hysol, but at $15/1.69oz I would need to mortgage the house. I did a bit of research and really like the reviews and specifications of a urethane sealant/adhesive called Sikaflex 252. It's about $13 for a caulk tube. I have one on order from McMaster and am going to conduct some failure testing against silicone. I will post some results and also advise on disassembly feasibility.

[edwardb]

Just for the record, the silicone is intended to do more than just waterproof the joint. It does in fact provide a structural bond. I've had to take apart several panels after they were assembled with silicone and rivets. In a couple of cases I had to make new parts because they were damaged trying to get them apart. Not saying that something else might be stronger (and probably is) but is it necessary? I'm not so sure. This method has been successful thousands of times now. Just saying.

[Blwalker105]

Yeah, overkill is in my genetic makeup. Probably not going to be a budget build.

[wallace18]

After building 5 FFR kits I have to say silicone is the way to go. But it is your build and do what you se fit to be done.

[edwardb]

Yeah, overkill is in my genetic makeup. Probably not going to be a budget build.

I've never been accused of budget builds :eek: so that's not really the point for me. There are dozens of decisions during these builds where something can be "better" but the bigger question is whether it's really necessary. This is likely one of them. Good luck with your build and whatever you decide.

[Jeff Kleiner]

I'm with edwardb and Wallace. I've also built a multiple cars...no regrets or reason to use anything other than GE Silicone II in my opinion.

Jeff

[oldguy668]

I've done 2 kits with silicone, 1 with 3M VHB tape, and 2 with Bostik 1100 (sold by Breeze). I recommend the Bostik because it's strong, easy to apply neatly, and paintable.

[russelljones48]

Since I was interested in this post I just did some quick research and the PDS's for both products state a tensile strength of 213 psi for the GE SII and 240 for the Bostik. Although it probably isn't the whole story it's not enough of a differentiation for me - especially given the price and availability of the GE SII

[PapaBear]

I have been to build school, but I have forgotten. Are standard rivets aluminium or ss? I thought aluminium.
Any long term corrosion issues between the steel frame and aluminium panels/rivets?
Galvanic corrosion should be expected between the steel and aluminium. Silicone and ss rivets should prevent the issue almost completely.

[Zach34]

If you want to epoxy your panels in, more power to you, but if your goal is to make the frame stiffer you would be better off welding in additional steel rather than gluing panels in. The rivets are aluminum. The galvanic corrosion discussion has been tackled before and it gets pretty ridiculous. IMO, unless you're storing the car outside next to the ocean you shouldn't have any issues.

That being said, never let an internet forum dissuade you from doing what you want.

[theburner9]

Anyone out there using alternatives to silicone for aluminum panel installation? I am looking toward strengthening the rivet bonding juncture instead of just waterproofing it. My neighbor is a race car fabricator and likes Loctite Hysol, but at $15/1.69oz I would need to mortgage the house. I did a bit of research and really like the reviews and specifications of a urethane sealant/adhesive called Sikaflex 252. It's about $13 for a caulk tube. I have one on order from McMaster and am going to conduct some failure testing against silicone. I will post some results and also advise on disassembly feasibility.

Where I work, we use Sikaflex 252 for a similar application. I'm tempted to try it on my next build. Being able to do all those aluminum panels with no rivets would be a huge plus in my mind. You almost for sure will need more than a standard caulking gun to apply the Sikaflex though.

And correct me if I'm wrong, but the aluminum panels aren't likely intended to add strength to the structure of the frame so simply bonding the aluminum to the frame with Sikaflex would be acceptable.

[edwardb]

And correct me if I'm wrong, but the aluminum panels aren't likely intended to add strength to the structure of the frame so simply bonding the aluminum to the frame with Sikaflex would be acceptable.

I thought that too, and said so some time ago on the other forum. I was corrected by a bunch of people saying the panels do add strength to the frame, by design. I haven't seen or heard any official response by Factory Five, but I suspect it's correct.

[jcjorgensen]

Using something similar on my build just because I am familiar with it. The link is where I purchased mine but you can find it from a lot of different places.

http://www.skygeek.com/sikaflex-0221243-90893-black-221-non-sag-poly-sealant-10-3-oz.html

I am 100% confident that any silicone would have been perfectly fine for my build.....but like a lot of the very experienced guys state on these forums, it is your build. In the aviation world I work with PRC-1440 and Sikaflex, both are used as galvanic protection when bonding dissimilar metals, installing fasteners wet, formed in place gaskets and sealing up everything from gas tanks to floor boards. Both of these are overkill but most all of our mods are!!

The nice thing of Sikaflex is it can be used in a normal caulk gun and cures even in very humid conditions (polyurethane). Hope this helps.

[6t8dart]

If you really want strength, 3M panel bond adhesive is the choice. Just don't ever expect to separate the panels from the structure, unless you use an air chisel. I saw a test once that two pieces were joined at a seam, and then mechanically pulled apart, the metal tore before the seam split.

[Blwalker105]

Well, informally, the Sikaflex 252 cures with moderately more hardness than silicone, but not nearly as much as I would have thought. I'll do more thorough testing today. The panel bonding adhesive is much more what I had in mind. I would definitely NOT think to use the Sikaflex product without riveting also...it has a lot of squirm. I would, however do that with panel bonding adhesive. I think a combination of pba and riveting would make for an incredibly strong and stiff structure. I feel that while silicone gets the job done just fine, one of the above methods may just provide another nth degree of margin for close encounters with both moving and inanimate objects.

For those who are multiple builders, a question:
Roughly how many tubes of silicone does a typical build require?

[edwardb]

Well, informally, the Sikaflex 252 cures with moderately more hardness than silicone, but not nearly as much as I would have thought. I'll do more thorough testing today. The panel bonding adhesive is much more what I had in mind. I would definitely NOT think to use the Sikaflex product without riveting also...it has a lot of squirm. I would, however do that with panel bonding adhesive. I think a combination of pba and riveting would make for an incredibly strong and stiff structure. I feel that while silicone gets the job done just fine, one of the above methods may just provide another nth degree of margin for close encounters with both moving and inanimate objects.

For those who are multiple builders, a question:
Roughly how many tubes of silicone does a typical build require?

Personally, I wouldn't omit the rivets no matter what adhesive is used. When you dry fit everything and match drill all the holes, that establishes your alignments. You will need to tweak some bends, occasionally do a little trimming, create some clearance for weld beads (just did that last week with some trunk panels), and you don't find all that out until you get everything properly pulled into place. Clecos and riveting gets everything back where it belongs, plus creates a tight joint allowing the adhesive to do its job. I think it would be very difficult and of questionable value to try the same thing with clamps, contact tape, whatever. Just my opinion.

2-3 of the large caulking gun tubes should be plenty, although I sometimes have trouble with it setting up in the tube once its opened because there can be some time between when you initially open and then use it all. And I've tried everything to seal them properly. I've had to buy another tube because a half full one wouldn't dispense any more.