General Weld vs bonding

[Hellkaim]

So...
As you may expect I have stumbled across some rust. Some of it I can repair with tin and soldering (not sure how to call it in English), but the other has eaten away some non structural panels.

Yes, I know that one should cut the beast out, make/get replacement metal part and spot-weld it back in place. At least what a conventional wisdom tells us.

But, as we are in 2026 i.e. XXI century why not to use modern technology or better say chemistry?!

I am speaking about 3m structural adhesive bonding line.

As far as I know the main 3 products in the field of weld free panel attachment are:

• 3M 08115
• 3M 08116
• 3M 07333

The main difference is a failure mode.

The 08115 is the strongest but it will partially pull itself from the panel in case of stress.
The 08116 is the one which will brake internally leaving a coat on bonded panels
And the 07333 is a mystery for me.

I know from a fact that nowadays Fiat recommends 08116 as it leaves that protective layer of adhesive in case of an accident not letting the metal to be exposed and rust to occur.

I am calling for our forum knowledge here: what should I use for repairs? Mainly I will do a small panel behind rear wheel arch (one facing the bumper) with intention to rivit it for additional strength (mot that I think it needs it but anyhow).

Thanks gor your opinions!

 

[bugsymike]

So...
As you may expect I have stumbled across some rust. Some of it I can repair with tin and soldering (not sure how to call it in English), but the other has eaten away some non structural panels.

Yes, I know that one should cut the beast out, make/get replacement metal part and spot-weld it back in place. At least what a conventional wisdom tells us.

But, as we are in 2026 i.e. XXI century why not to use modern technology or better say chemistry?!

I am speaking about 3m structural adhesive bonding line.

As far as I know the main 3 products in the field of weld free panel attachment are:

• 3M 08115
• 3M 08116
• 3M 07333

The main difference is a failure mode.

The 08115 is the strongest but it will partially pull itself from the panel in case of stress.
The 08116 is the one which will brake internally leaving a coat on bonded panels
And the 07333 is a mystery for me.

I know from a fact that nowadays Fiat recommends 08116 as it leaves that protective layer of adhesive in case of an accident not letting the metal to be exposed and rust to occur.

I am calling for our forum knowledge here: what should I use for repairs? Mainly I will do a small panel behind rear wheel arch (one facing the bumper) with intention to rivit it for additional strength (mot that I think it needs it but anyhow).

Thanks gor your opinions!

Speaking as a retired motor engineer who also was a Mot tester and foreman of a dealership many years ago, unless I got a direct Ministry of Transport directive regarding "bonded" panels I would fail them out of hand. Some years ago they banned brazing metal panels which some could argue flowed into the metal and joint far better, less likely to rust and lasted longer than some poor spot or tack welds.
As I understand it some specialist high performance cars are now using bonded aluminium construction, however it is done under modern robot computer controlled systems and if they have an accident later then a highly specialised repair has to be undertaken, certainly not left to your local bodyshop.
I am not saying the products you suggest would be weaker in the correct environment, just until widely accepted most people would reject it.

 

[Patjes]

Metal is still the same material as 100 years ago, Bondo, polyesther, cardbord, the neighbours-newspaper, are not the right materials for the job.
Cut it out, clean it properly and weld is in my opion the only way to fix it right. Rust always eats further until its structual, because you cant see it doesnt mean it isnt there on hidden places en structural placexs

It lost a good friend 2 decades ago because of a cheap conartist had bonded the sidesills on that bloddy Opel (Vauxhall) Astra, causing it to break in half on a impact not faster then 20mhp/h

 

[bugsymike]

Metal is still the same material as 100 years ago, Bondo, polyesther, cardbord, the neighbours-newspaper, are not the right materials for the job.
Cut it out, clean it properly and weld is in my opion the only way to fix it right. Rust always eats further until its structual, because you cant see it doesnt mean it isnt there on hidden places en structural placexs

It lost a good friend 2 decades ago because of a cheap conartist had bonded the sidesills on that bloddy Opel (Vauxhall) Astra, causing it to break in half on a impact not faster then 20mhp/h

When I was doing Mot's some of the rubbish that came in for testing was frightening, newspaper and polyester resin was common with a good coat of under seal. Had one bloke who couldn't understand why I failed a structural wing that should have been welded , he had spent days drilling and bolting hundreds of 2BA nuts and bolts in it. I told him he would have been better asking a bodyshop to weld it on probably for less labour than he could of earned at his day job instead of doing the drilling and bolting.
Brakes pipes covered in grease as though the rust would go away, others where they had polished/sanded the rust away so the metal was paper thin.

 

[Hellkaim]

covered in grease as though the rust would go away

Oh, gosh - that's the classic one.

No no, it is (a) not structural and (b) it might actually be a good idea to cover it all in grease, spray some gasoline on top and watch it burn. At least it will reveal all the rusted spots faster!

 

[Patjes]

3M is very clear on there dutch site: ( i am from the netherlands, therefor the dutch site)
The 3m products you mentioned are with a big disclaimer from 3m to only used by trained proffesionals.
and NOT to be SOLD to private people,
Here in Holland you need a license of a certified company before even the purchase can be done.
3M doesnt do things like this without a reason.

 

[Hellkaim]

bonded the sidesills

My condolences. That part of the car can't be bonded unfortunately. But.. yeah.)

Ok, I got the idea.

I will fabricate the replacement anyway and then talk to some local chaps to see what they can offer in terms of welding.

I am.mostly asking abou the 46724075 - joining element under the rear wings (see ePER breakdown

 

[Hellkaim]

That is the part in question.
We are looking toward the wheel from the back of the car upside-down

 

[bugsymike]

That is the part in question.
We are looking toward the wheel from the back of the car upside-down

Personally if it was steel originally, I would make up a plate in steel, clean and prep the area and make safe from fire risk , then ask your local chap to weld it, then clean , derust, seal it and paint well.

 

[Hellkaim]

if it was steel originally

There is not much on B that was not steel in regards to the body.