Gluing in floor pans?

We see more and more adhesives in cars, roof panels, door skins, etc. Makes me wonder about gluing in floor pans. I know the welding is not that bad. But, if you're paying for it; there is cost/benefit. Thoughts?

Let me start with the fact that I'm a retired welder that has replaced 1,000s of floor pans over the last 28 years.

Bonding floor pans can be done if you are replacing individual pans as long as you don't need to replace the body structure that the pans are attached to. If its just the floor pans, it may even have an advantage bonding the pans in because the process seals the pan to the metal they are bonded to which likely will prevent future rust forming at the seam.

There is at least one disadvantage to bonding in a floor pan, the bonded area is an overlap. The new pan has to over lap the original pan by about a 1/2" all the way around the old pan, and that seam will be visible from under the car, if that is something that would concern you. Bonded panels are not butt welds that so many here are concerned about. A properly done bonded pan would have to have all of any paint or surface protection removed from both bonding surfaces all around the pan. Properly done, the bond is suppose to be as strong as any weld.

If body structure that supports the floor pan needs to be replaced, that replacement floor support needs to be welded into place, then the pan can be bonded to the welded in support.

It is not recommended for a full replacement floor pan assembly to be bonded to the body without several welds.The stress forces of the body to floor pan that is only bonded in place without welds, can cause the bond to fail. Unless the information has changed recently, a panel under stress was not intended to be bonded in place without additional welding support. Gene

i am a certified autobody tech with 35+ years experience.

i bond panels all of the time. every panel i bond also gets welded with squeeze type spot welds just like the factory uses.
the I-Car gold, VW certified bodyshop i work at uses 3M adhesive exclusively. it's says in the instructions to NOT USE IT on floor pans and rear body panels. my guess why is they get to much vibrations and flexing and might break the bond seam. once the adhesive drys it's very hard and rigid.
if you must use it i would recommend the impact resistant panel bond, 07333, over the regular bond adhesive.

A lot of years ago, 10 or 15, I called Fusor because their instructions said not to use it on rocker panels, and a few other areas. they told me the National Traffic Safety Board required them to warn against that. I forget the details, but it had something to do with the "crushability" of the car. there was also something about the "tension" strength being as great as a weld, but it was not the equivalent of a weld for 'shear" strength. In other words, it could be "peeled". As I said, that was a lot of years ago. I expect things have changed.

I love the things I can learn here every day.
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- Art

Always top notch info from Mr. T.

I'll add to that by saying if you're talking about bonding vs. welding on a resto of a 60s/70s car or similar, you can do whatever you think is best. If you're talking about collision repair on a modern vehicle, you should only do what the manufacturer dictates in their OEM repair procedures. For example don't bond the roof if the OEM calls for welding it. Google John Eagle Collision Center if you want to know why.

Google John Eagle Collision Center if you want to know why. [/quote]


What an awful experience for that family.

I've also welded in many floor pans.. Here's a reason I wouldn't want to rely on glued in panels, if you're involved in a collision in a unibody car do you really think a glued in panel at your feet and legs will stay in place? I sure wouldn't want a floor panel pop loose during a collision, it would be like a giant razor blade buzzing around at your feet and legs cutting everything it touches. Being in a car crash is bad enough, now you multiply the danger with sharp edged steel cutting your feet off, not for me. Weld those floors in place.

I used to have a Grumman airplane which was entirely glued together.

Do you really think the OEMs who design, test, and build the cars would specify bonding instead of welding if the floor would "pop loose" in a collision? If the guys who design, test, and build the cars say bond the panel instead of welding it, you bond it. It's that simple. Also, bonding is actually stronger than welding, depending upon the application.

"depending on the application" is the key.

strange things happen during accidents, so i won't recommend anything because of this.
when i was a fireman back in the 70's, i responded to a scene where a guy was trapped in his vehicle during a multiple vehicle accident.
his leg was trapped through the floor pan when the inner kick panel structure separated from the floor pan, his foot fell through, then the panels closed up trapping him. he was lucky to not loose his foot.
this particular accident had two fatalities.

now with that said, over my life i have built and modified countless items that have been against many "norms", some surviving "destructive" tests without any damage what so ever.
structural adhesive is a great product when used correctly, and i'm sure i will use it in an "inappropriate" application during my lifetime.
will it work out for what i will use it for ? who knows.........
just stating about me.
your results and mileage will vary.

If we're talking rust/resto work on an old car for which there is no OEM repair procedure, it would be best to research the types of adhesives that are available and applicable to the job at hand to see if they are a viable option. If we're talking collision repair on a vehicle for which there is an OEM repair procedure, you do what the procedure says, period. If it says weld, then weld. If it says bond, then bond. Anyone who deviates from that is a hack and an effing moron.

Welds can also separate during accidents.
One advantage to gluing it in is if done properly it's completely sealed and there's no heat involved that can cause rust in those areas.
Adhesive manufacturers claim that the bond is stronger then welding but on the other hand we all know how adhesives and chemicals can change with age and I'd tend to trust a trailer or roll cage that was properly welded vs one that was glued together. Different then a floor pan I know but still...

If rust was a "principle" motivation for bonding; then of course oem's could find a way to implement it AND justify it's use. Also HSS materials have been in use for some time & use bonding. Older cars did not use HSS materials. Something to ponder.

I'm sure corrosion prevention plays a role with the OEMs in some instances, but strength, energy transfer, and repairability are likely higher on the list. Some of the cars are manufactured with processes that cannot be duplicated by a repair facility, and in many of those cases, the OEMs specify bonding as the proper repair procedure, even though those parts were welded at the factory.

I read that John Eagle story. Sad. but I have 2 things to say about it
1) In the story, was something about State Fraud (OK, State Farm, I have my reasons for not being happy with them, as a customer of theirs-- nother story) putting pressure on the body shop to "control costs" and how the insurance company can override factory specs and procedures "by not paying the bill" Why would State Fraud not have been held at least partly liable in that case? They are driving the process and procedures by trying to drive everyone to "go cheap" and put lipstick on pigs so to speak... haven't we heard enough, about their demanding "similar" aftermarket parts instead of OE parts and the lawsuits of a few years ago relating to that? (also in the name of "fixing it cheap")
I would rather go to a junkyard and get say a good used OEM fender or bumper, than to use some of the aftermarket crap body panels on the market today. They don't fit right, the body lines "don't quite" line up, as don't some of the mounting points/// and as years have gone by, the OEMs have done more than enough in thinning out the metal used in body panels.... they DON'T need any help from the aftermarket, in thinning out panels....

and 2) a Honda Fit?? Cmon now.... not like that tiny little go cart would have had any hope of standing a crash vs a pickup truck, even if it hadn't been for the previous repair, the owners of such tiny cars should be at least partly liable because of their choice of "wheels" in the 1st place.
I mean its unfortunate what happened to this guy..... but nobody held a gun to his head and told him he had to buy a micro mini car, way smaller than even a "compact" car. Back in the day A bodies were "compacts, there's enough metal in an A body to build at least 2 Honda Fits. For that aspect of laying fault I think the victim should bear at least some portion of blame in that case. I don't think that he would have fared much better, if any, had he been in a Fit that had previously never been wrecked or otherwise damaged, and was exactly as it left the factory when new.

On the panel bond; my son has a 99 Dodge V10 powered, 2500 4wd. he got a pile of reciepts with it, from work done by a PO.... several of them for patch panels, Panel Bond and paint; the truck looked pretty decent 1-1/2 years ago when he got it. This truck is cab and a half with the back "1/2 doors" that open suicide style. the back doors apparently have at least partial skins on the bottoms, and stick out like a sore thumb as it looks like they slathered the panel bond on much like Bondo would be. When he got it the rockers and bedsides looked perfect. this is the 2nd winter he has owned the truck. Last spring, we noticed rust popping on the bed in weird places. Looks like right where they would have cut the wheelwell arches to replace with bedside repair panels. You can now see exactly where the panel bonded seams from having replaced those bedside wheelwell arch panels sometime in the truck's past. It looks awful. so for me? I have to say NO way to panel bond.
We also know someone that panel bonded quarters on a 64 Galaxie. That car looks AWFUL now, though it looked great when the job was initially done. so for me, I'll weld new sheet metal in when need be, no "panel bond" for me!

sorry to hear about your repairs on the truck.

just a FYI...panel bond isn't designed to be used on anything except the factory joining locations between 2 panels. or otherwise know as the factory lap joints, like where the 1/4 panel meets the outer wheelhouse in the wheel opening moldings screw into. of the pinch weld flanges under the glass bonds to or where weatherstrip goes over in the jambs.
it's not designed to be used in the middle of a flat panel near a body line where a lot of people sectioning a lower panel to a upper panel. you will have the same problem like using fiberglass to fill seam joints instead of body solder on older cars. there will be expansion differences and the seam will show up when it warms up. i have seen a LOT of shops use it that way and have the problems you describe later on.
it also doesn't like to have body filler spread over it. this will lead to adhesion problems and rust forming under the paint like you describe. if you HAVE to use it that way, CLEAN the lap join as best as possible to remove as much adhesive as you can. after that spray a couple of coats of epoxy primer down to seal off the area and then scuff up the epoxy and spread filler over the epoxy. you will still have expansion problems but there won't be any adhesion problems.

State Farm was dismissed from the suit. There was no proof that SF told the shop to do what they did. For the sake of discussion, let's say that they did, though. It's still the shop's responsibility to repair the vehicle to OEM specifications, using OEM procedures. If an insurer pressured a shop to deviate from OEM procedures, the shop has several steps they can take, including involving the customer. That's why SF was dismissed, and the shop was held liable. IMO, the people who worked on that car and oversaw the repairs belong in prison.

Also, you can try to blame all you want on the fact that the car was small, but people who know far more about the dynamics of an automobile collision stated unequivocally that the energy load path was changed by bonding the roof instead of gluing it. With that being the case, a similar result could've been expected on a larger vehicle as well. In fact, it may have been worse in a larger vehicle, given the increased weight adding to the impact with the pole.