Structural adhesive on seams

Hey what's going on guys I have a 97' thunderbird. It's completely stock engine wise, but has a good amount of suspension parts. The purpose of this post is to find out how many of you guys have used structural adhesive OR any kind of panel bonding adhesive on the seams of the unibody? 
 

ive recently come across this where people seal the seams with these adhesives and it help out with the rigidity of the car. By how much I'm not sure, one thing is for sure. It's a lot cheaper than finding somebody to stitch/seam weld up the whole car. 
move seen the new type R civics have seam sealant all around the shock towers and many other areas.

https://forums.nicoclub.com/project-garage-pignose-hatch-build-t608543.html

here's an example of sombebody who did it on a 240sx. by the looks of it he simply cleaned up all the seams and then sealed em all up. I was hoping to use it in the e tire engine bay, interior/roof and possibly the trunk area. Also if this works good enough I'd say it's eve possible to hit the underside where the frame rails and body meet up. 
 

obviously my car is a lot older and has ZERO sealant anywhere in the engine bay. 
 

anyways, who's tried it? 
 

thanks in advance!!

I haven't tried it. 

I have done full seam welding, and stitch welding. 

Im skeptical of the adhesive being applied to surface doing much, but hopefully get proven wrong as it would be WAY easier on finished cars.

Putting panel adhesive on top of the seams won't do anything for rigidity.

It says right in the thread it is for non-structural use.   And that is when it is actually bonding the two panels together by being sandwiched in between the panels that are bonded.   There is absolutely no way you are going to get it in between two panels that are already spot welded together.

Panel bond adhesives require a surface area to create a strong bond.  This is the area where the two panels overlap when they are bonded.

There is no significant surface area when the panel bond is used on the outer seam where the panels meet.

I just stitch welded my NB Miata. There was a HUGE quantity of structural joints that were primarily bonded with adhesive. 
 

Standard method is spot welds spaced too far apart, and adhesive holding the panels together. 
 

Note that I stitch welded. So, I was looking for more structural rigidity than the adhesive was offering. However I do intend to seam seal the whole car with structural adhesive (in addition to the welding). 
 

YMMV

In the article the guy says they did it on his friends mini and it made a huge difference. And also 3M sells another one called "structural adhesive" and that's the one he was referring too. It supposed to be great for repeated impact areas aka my damn shock towers. I don't see why it wouldn't work, if you can get just a bit in between the seam and a good contact patch up top it should be able to hold at least a lil bit. I bet it's more for NVH on most new cars.

so has any body done it on here? I'd like to try but would want to pull the motor when I swap to a 4v and do everything up in there. As right now I'd only be able to get to the easily accessible areas. 

In reply to SV reX :

Not sure where you would be winning this war.

Panel adhesive lets go if you heat it to 350 ish degrees. That is for 3M 8115, so I expect it to be representative.

I suspect that the longer distance between spot welds on the Miata is to avoid damaging the glue bond. Also guessing the glue is the primary strength provider in the assembly and the spot welds are just there to hold parts in place while the glue dries.

If you stich weld or seam weld the tub, I imagine you would get the surrounding metal hot enough to release the panel bond. Overall, I see less rigidity from seam sealing  a chassis that was glued together.

Noser7 said:

And also 3M sells another one called "structural adhesive" and that's the one he was referring too.

No, he's not-

3m 8115

Note: Panel Bonding Adhesive should only be used to bond structural components such as pillars, rockers or frame members when specified by an OEM (Example: Aluminum Ford F-150). Unless specified by an OEM, structural components should be welded.

It's been said above in this thread, but you need a decently sized area to bind PLUS proper surface prep.

I would very seriously question if just laying down this adhesive on existing joints will do much. It may have a sort of placebo effect in that it might quiet some rattles or eliminate gaps that sound was getting through, so a quieter chassis might trick someone into thinking it was stiffer. 

BA5 said:

It's been said above in this thread, but you need a decently sized area to bind PLUS proper surface prep.

I would very seriously question if just laying down this adhesive on existing joints will do much. It may have a sort of placebo effect in that it might quiet some rattles or eliminate gaps that sound was getting through, so a quieter chassis might trick someone into thinking it was stiffer. 

id be happy if it even did that to be honest. I've noticed most new cars use it in a lot of locations. 
id say since your sealing up the whole seam from end to end, in conjunction with the stock spot welds it should make for at least a quieter ride. At most it'll cure a lil bit of flex, which is much appreciated. I've been looking at the civic type R and their use of sealant over the seams. It's like the liberally apply a bead over both seams. I have some pictures so you see what I mean. 
 

you see all that sealant? That's what I mean, on my bird there is not a single bead of anything there only spot welds. If the manufacturers do it over the seams, there has to be a reason for it.

NOHOME said:

In reply to SV reX :

If you stich weld or seam weld the tub, I imagine you would get the surrounding metal hot enough to release the panel bond. Overall, I see less rigidity from seam sealing  a chassis that was glued together.

Why?  Is that a typo?  Did you mean you see less rigidity from seam WELDING?  I can see the argument that breaking the panel bond could lead to a less rigid connection, but I don't see the any reason why seam sealing an already welded chassis would be a bad idea, or lead to less rigidity.

You're right. The heat should release the panel bond. Plus, you need to get most of it out of the joint to have good welds. 
 

That's exactly why I want to do it. To re-bond any gaps possible after the welding. 
 

I also want to seal the gaps to prevent moisture from getting in the joint and starting to rust. 

In reply to SV reX :

Standard method is spot welds spaced too far apart, and adhesive holding the panels together. 

You did mention that the spotwelds in the car were further apart than in earlier cars where there was no adhesive used, and that would make sense since the glue is doing most of the work and the area directly around the spotweld is going to have the glue compromised by the heat of the spotweld.

If heat from seam sealing damages the glue, and there are few spotwelds to take up the load, then the car might not even be as solid as it started before you did the seam welding.

Noser7 said:

In the article the guy says they did it on his friends mini and it made a huge difference. And also 3M sells another one called "structural adhesive" and that's the one he was referring too. It supposed to be great for repeated impact areas aka my damn shock towers. I don't see why it wouldn't work, if you can get just a bit in between the seam and a good contact patch up top it should be able to hold at least a lil bit. I bet it's more for NVH on most new cars.

 

so has any body done it on here? I'd like to try but would want to pull the motor when I swap to a 4v and do everything up in there. As right now I'd only be able to get to the easily accessible areas. 

I have experience using regular panel bond as well as 3M 07333 structural adhesive joining unibody panels and both have their place. These types of materials are designed to be applied to properly prepared metal and then tightly clamped together in order to provide the intended structural integrity. Failure to prep the surfaces and/or pinch the pieces tightly greatly reduces the ability of the adhesive to function as intended.

I also have experience fully welding frames, adding strategic welds to frames, reinforcing frame areas, and adding welds to unibodies.  

Was there any actual "testing" of the structure of the Mini?

When 3M refers to "impact" areas they're referring to crumple zone areas, here's an excerpt from their website concerning the 07333 product below.

"Impact Resistance and More
3M™ IRSA is designed to absorb collision energy forces and delivers increased torsional rigidity for OEM-specified automotive structures. It allows for spot-welding (form squeeze-type) in an uncured state, typically up to three hours after application. Properly applied adhesive will seal joints completely, and perform when exposed to very hot and cold temperatures. Its corrosion inhibiting formula delivers lifetime corrosion protection. The cured adhesive can also help decrease NVH (PDF, 325.12 Kb) in the vehicle."

The "spot welding" that can be done when the structural adhesive has first been applied is pinch type resistance welding NOT the mig/tig type plug welds many DIY people use.

Simply squeezing adhesive into voids between sheet metal panels probably won't do much because the surfaces can't be properly prepped so you'd only have a bond between the adhesive and whatever paint/primers rather than prepped bare metal. Plus the adhesive would be too thick. Smearing adhesive on the outside of sheetmetal joints will have little if any benefit.

These products are excellent at preventing corrosion, but, only on properly prepared surfaces. On surfaces where they may loose their adhesion due to paint/primer/dirt etc. they may actually increase the risk of corrosion by creating tiny cracks between the adhesive and body panels that wouldn't dry out as quickly as the same type areas that didn't have adhesives applied.

Be aware that the 07333 structural adhesive requires a different gun than the  08115 panel adhasive should you attempt this project.

Seam sealing with seam sealer may provide some reduction in NVH by dampening the body panels a bit. And, a quality seam sealer would probably do a better job of keeping water out of seams over a long period of time in most cases than the adhesives.

Overall, IMO,  using structural adhesives and/or panel bond on already assembled body parts is a waste of time and money compared with the minimal performance increase that MIGHT be obtained.

NOHOME said:

In reply to SV reX :

 

Standard method is spot welds spaced too far apart, and adhesive holding the panels together. 

You did mention that the spotwelds in the car were further apart than in earlier cars where there was no adhesive used, and that would make sense since the glue is doing most of the work and the area directly around the spotweld is going to have the glue compromised by the heat of the spotweld.

If heat from seam sealing damages the glue, and there are few spotwelds to take up the load, then the car might not even be as solid as it started before you did the seam welding.

I get the theory. Except that's not what experienced racers with my chassis have found (including Keith Tanner and Flyin Miata)

I took the welding plan directly off Flyin Miata's website (including the direction to remove as much sealant as possible to get good welds). 
 

I feel very good about my plan. I'll skip the theoretical. Thanks!

I hear ya loud and clear, I had been wondering if ANY body on here has fiddled with this but it seams like not really. Personally I'd like to try one day in the future, I mean it won't hurt anything regardless so I don't see any harm in it. If it were to work even a tiny bit great, if not it's always a learning experience.

Thanks!

Noser7 said:

BA5 said:

It's been said above in this thread, but you need a decently sized area to bind PLUS proper surface prep.

I would very seriously question if just laying down this adhesive on existing joints will do much. It may have a sort of placebo effect in that it might quiet some rattles or eliminate gaps that sound was getting through, so a quieter chassis might trick someone into thinking it was stiffer. 

 

id be happy if it even did that to be honest. I've noticed most new cars use it in a lot of locations. 
id say since your sealing up the whole seam from end to end, in conjunction with the stock spot welds it should make for at least a quieter ride. At most it'll cure a lil bit of flex, which is much appreciated. I've been looking at the civic type R and their use of sealant over the seams. It's like the liberally apply a bead over both seams. I have some pictures so you see what I mean. 
 

 

you see all that sealant? That's what I mean, on my bird there is not a single bead of anything there only spot welds. If the manufacturers do it over the seams, there has to be a reason for it.

Look at the location of all that sealer. Inside the wheel well, right where nice salty water will get driven into seams every winter by the tire splashing it up.

I've used 3M panel bond to hold wheel tubs to a truck bedside. The stuff has like a 400lb/sq.in. pull apart strength. Give it a flange to grab and I'll take it over welding in some locations. The problem is you aren't getting it between the seams, its on the surface. Before I would put any on a car that way I would lay out a bead on some plastic and spread it thin. Then test how easily it flexes or even tears. If it does either, it isn't going to do much for you.

In reply to jgrewe :

I see what you mean, it won't do squat if it doesn't reach INSIDE the seam aka from the factory. Buuut have you seen some of the seams of 90's Ford? My 97 in particular has slight visible gaps between seams. I was thinking of heading up the whole seam, using my finger to get it up in there and then applying another bead over all that. By the looks of it they even put it in the engine bay as well not just the underside. 
 

I also have these pictures from a Lexus RC-F which has the same seam sealer in the same places. 

Side note, this Lexus has a fender brace from the factory. Makes me also want to try and make a set for my car as well. Simply triangulation of the fender cowl area.

OK

First thing I see is that people are confusing "seam sealer" with "panel adhesive" NOT the same thing.

Seam sealer is a moisture barrier and to some degree minimizes NVH. Adds zero strenght to a structure.

Panel bond is an epoxy product that is meant to join two metal panels together  via a lap joint with a well defined surface area and glue bond thickness.  Both surface area and glue line thickness are critical factors.

Experiment:

Take two strips of tin and lay the two side by side. Lay a bead of panel bond on the top of the seam.

Take another two pieces of tin lay them side by side and run a bead of weld down the seam.

Now bend the two  along the seam line and let me know if there is a difference. 

NOHOME said:

 

If heat from seam sealing damages the glue...

I agree. Lots of confusion here. 
 

You have twice used the phrase "seam sealing" when I think you meant "seam welding".  I'm trying to clarify what you are trying to say. 
 

Above quote... there is no heat from seam sealing. So, the comment is confusing. 

In reply to SV reX :

You are correct.  

structural-adhesives-brochure-interactive.pdf (3m.com)

Strength in shear is given in the attached table at about 20 to 28 mPa; depending upon the part number of the particular adhesive selected. 

So the table translated to US units is 2.9 to 4 ksi (kips per square inch) (1 ksi is 1000psi.)    4 ksi = 4000 psi  

So the adhesives have strength in the range of concrete (though concrete has just about zero tensile capability)

Welding rods have an overall shear strength of  60 to 70 ksi. 

 Fillet welds with a 70ksi rod have a strength of 0.92 kips/inch per 1/16" of weld rod applied. 

If you want to make a chassis stiffer you would be better off filling the rockers and front horn above the strut with 2 part urethane foam. Get the 2lb /cuft stuff.

It may, or may not, have been a trick used in showroom stock racing years ago. Even if it was you can't prove I did it...

We use 8115 as a "seam sealer" of sort. But we go back and dress the seams afterwards for a cleaner look before we finish off our floors. 

As far as added strength even "shoving it in" with a finger... I highly doubt it. We are using the product in ways not intended. The prep work for a proper bond between the panels is not possible, nor is proper clamping procedures. We aren't using it like this for strength, we are using it to clean uo the appearance of seams. 

If it *does* add anything strength wise it would be in the single percentage ratio. You'd be much better off properly seam welding the chassis, for the effort required.  Preparing the floors and getting that E36 M3 to stick, and knocking it back so it doesn't look like a bag of isht, is a LOT of work. 

Were it mine, I'd prep the seams and seam weld it. Even using silicon bronze in some areas, similar to how factory backed motorsports shells are done. It's just a much better end result if you're after increased stiffness.

jharry3 said:

structural-adhesives-brochure-interactive.pdf (3m.com)

Strength in shear is given in the attached table at about 20 to 28 mPa; depending upon the part number of the particular adhesive selected. 

So the table translated to US units is 2.9 to 4 ksi (kips per square inch) (1 ksi is 1000psi.)    4 ksi = 4000 psi  

So the adhesives have strength in the range of concrete (though concrete has just about zero tensile capability)

Welding rods have an overall shear strength of  60 to 70 ksi. 

 Fillet welds with a 70ksi rod have a strength of 0.92 kips/inch per 1/16" of weld rod applied. 

 

Let me start by saying you are much smarter than me. I'm just trying to follow along...

I think the case you are making is that the adhesive bond is stronger than the weld. But I have a few questions...

The first is that you are comparing the area of adhesion to the linear length of weld. I don't think that is a valid comparison. It needs more maths.

The other thing is that there are very few places on a car where the forces would be pure shear. (Now I'm in over my head). 
 

If 2 pieces are trying to slide past each other, the joint would be in shear. (Perhaps a joint between 2 pieces in a door sill of a convertible). 
 

But a shock tower reinforcing plate is probably being exposed to cleavage stress when cornering hard. The same tower plate in an off-road vehicle may be dealing with tensile stress when the vehicle lands hard after a jump. 
 

Seems to me overall chassis rigidity is defined by many more forces than  just shear, and that it is hard to compare welded joints to bonded joints when just comparing bonded area to linear welds. 
 

I know this is off topic a bit. There are two different subjects being discussed... 1- panel adhesive used as seam sealer (I agree. Probably not worth the effort), and 2- bonded panels vs welding (I'm still in the camp that believes in seam welding, even if it risks compromising factory adhesive bonds. I would then want to do whatever was possible to reseal and/or bond the joint after welding)