Whaddya think: Weld or Epoxy?

[Wrecked944]

Okay, so I got this very rusty 1973T targa for free...yes, free. Problem is the bottom is rusted. So I bought brand new floorboards from Resto Design which are sitting in my house right now. But now I'm feeling frisky. Would it be better, worse, neutral to afix those floorboards to the chassis with structural epoxy instead of welding them?

[Formerly Steve Wilkinson]

I have found that stuff like JB Weld, which _can_ be excellent, is so subject to the need for perfect surface conditions and cleanliness that I'd opt for welding. I just spent months trying to JB Weld a slightly cracked household radiator--cast iron--and simply couldn't get it to work no matter how much I Dremel-ground the surface to get it clean, no matter what solvents I used to wipe it off. Finally replaced the area with a new piece.

[EarlyPorsche]

I wouldn't consider anything but welding it in. If you fit it I am sure a qualified mobile welder could finish the job for you.

[Wavey]

One issue with epoxy would be clamping the floorboards in place while the epoxy cures. Unless you have some very large, very trick clamps, it's going to be hard to reach some areas to clamp them. I guess you could use Clecos or screws and fill the holes later.

[the]

you forgot option 3: Pop rivets.

[Wavey]

Originally posted by the
you forgot option 3: Pop rivets.

There you go... or bent-over nails

[Porsche_monkey]

You can buy automotifve structural adhesives at your auto parts store. They are applied with a caulking gun.

Since I know how to weld I would never consider them, and I wouldn't be too keen on buying, or driving, a car that had new sheet metal glued to rusty old sheet metal.

Welding is the right way to go, IMO.

[scottbooth]

I have not been able to find any strength specs for structural adhesives besides JB Weld.

JB Weld specs their tensile strength at 4000 psi. By comparison a little research on the web gave me values between 35000 and 60000 psi for mild steel. There are other specs for shear strength etc. but you get the point.

I know that bonding is used in the manufacture of cars, bike frames, etc, so I would assume there are adhesives that have properties closer to that of the metals being bonded. But I would be concerned about the process as well - I imagine this industrial bonding is done in a much more controlled environment than the typical home garage.

I am curious about this because I am trying to repair some rusted areas in my 911 tub and some of it would be easier to bond than to weld, due to accessibility issues, but I still think welding is probably the best option.

Good luck,
Scott

[fty]

Id rivet them..or weld them.

[1982911SCTarga]

From a resale, restoration and originality viewpoint, welding is the only way to go.

Brian

[dogslovetrucks]

Rivets, JB weld, bent over nails and a big gob of chewing gum should all go in the same catagory here. Welding is the ONLY option IMHO

[Gearbox]

I wouldn't use JB weld, but there are specific epoxies to do this job made by 3M. As you all may know, most all new car manufacturers use this stuff religiously to mount quarter panels, roofs, door panels, etc. Although it is not meant for "structural" parts, it can be used in your application with rivets. Generally speaking, rivets every inch will give you a structural bond. However, the epoxy has a tremendious shear strength as well, so coupled with rivets every 3 inches should be more than sufficient. I've done this on inner and outter rockers, sectioning panels, and headlight buckets with great success and longevity. Rock solid.

Now here are the positives and negatives. The good is no welding, no weakening or distorting the panel with heat, and it's clean and easy. Since the epoxy runs along the entire surface, you have no air gaps between the bonded panels that would promote rust. The bad is that you have to make sure there is zero rust on the bonded surfaces. Rust will seperate the bond in no time, so you have to make sure it's super clean. The product is about $60 a tube and needs a special gun ($400 and not worth it, it's just a double piston chaking gun) to squeeze it out, but if you are handy, you can make the gun (or borrow it from a body shop).

Overall, my experience with the product has been great. After years of service, I have yet to detect any fatique or failures. But prepping the surface is the key. Good luck Allan

[DanielDudley]

Gearbox is correct. I once saw a Mach 1 Mustang with lapped, bonded and riveted repair sections on various sections of the car. They could only be detected by pulling off interior trim, and were viable permanent repairs. The new owner decided to redo all the body sections with welded in repairs. Due to the skill levels of those involved, he basicly ruined the car.
The moral ? A well executed patch is better than a hacked up weld. If you want to do it yourself, consider your skill levels, or consider increasing them. I learned to weld at a local vocational school in a night class. I understand that videos are now available, as well as affordable MIG welders, probably the easiest type of welding to learn. LOL

[Shaun @ Tru6]

The Miller 135 awaits.

[niner11]

Lincoln 140c or Millermatic 140 both are good for the money. Probably get set up with gas and a mask for 750.00 or less.
You would spend at least half that having someone else do the work

[kmhemi]

Better weld those. Leave epoxy for panels that aren't part of the cars structure and strength.

[Gearbox]

DanielDudley makes a good point. I have Oxyacetoline, Mig, and Tig welders. After years of playing around with these, I have mastered oxy welding and brazing, and pretty good at mig. But the Tig still alludes me. Outside of welding heavy gauge metals, I still blow holes in body panels with the tig. But back to the point. Buying the equipment and learning how to use it is always a good thing, but welding is much like an art where many many hours of practice will only get you to adequate welds...and that's a big maybe. Getting perfectly spaced "fish scale" welds may be beyond many of us no matter how many hours and lessons we have. So getting a current project done correctly and thinking that all you have to do is to buy a welder with no previous experience would be IMO pretty optimistic.

In certain applications, welding is a good thing, especially at the hands of an experienced welder. But the problems are numerious. Put too much heat on the panel and it will be guaranteed that the weld area will quickly rust out if not distort it immediately. Trying to butt weld is very difficult and over laping panel welds are usually done with one inch beads intermetently spaced so as not to heat the metal too much and distort the panel. This leaves an inch or so of bare metal around the entire repair that would be prone to rust.

The 3M panel epoxy isn't the cure for everything, but after using it for quite some time, I'm sold and use it when ever I can. As for the floor pan, It would depend on the extent of the rusted out areas. Which pans did you get? Full left and right sides, front and back, or just quarter sections? If you can cut back leaving about an inch of good clean metal to overlap the new section you're golden. Just clean both sides to bare metal, tweek the overlapped sections so you get a perfect flush fit, drill 3/16" holes through the overlapped sections every 2-3 inches, and coleco the panels as you drill. Once you are happy with the fit, remove the colecos and dril the upper panel with a counter sunk bit. Apply a liberal amount of 3M epoxy mix to the lower panel and fit the repair panel. Rivet the panels together before the epoxy dries with 3/16" stainless steel counter sunk rivets. I use some of the excess epoxy that squishes out to cover the rivet heads so it will be invisable once painted. The underside of the floor where the rivet sticks out can easily be covered with Wurth grey undercoating to make an undetectable repair. As long as you have clean rust free metal to work with, the repair should last decades. Good luck Allan

[ed martin]

If I recall it says right on the tube of 3M epoxy not for structural use. A good weld is stronger than the original metal. The floor has a lot to do with the structure and rigidity of the car overall. If that's not convincing enough, wouldn't you feel better cruising at highway speeds knowing the floor is solidly integrated to the frame without that bothersome concern that you and your passenger could just fall through the floor at any given moment because you tried to save money by gluing it?

[Gearbox]

You are correct in that panel epoxy is not recommended for structural sections by itself which I had mentioned in my first post and I also agree that a "good" weld is stronger than the metal itself. But the point I was trying to make was the chances of a first time welder with a new piece of equipment is probably not going to yeld a "good" weld. But the combination of the epoxy and rivets will provide more than sufficient strength. Monocoque race cars chassis' and aircraft are all assembled in this maner with no issues to structural integrety. The 3M product has a 4000 PSI adhesion strength and the 3/16" rivet has a 1000 pounds of shear strength each, so no, your floor won't just fall out. BTW 911's don't have frames rather it is also a monocoque construction.

[mb911]

since a floor pan is spot welded in it would be pretty quicl to pick up by the beginer the basic skills to do that. spot welders around here make about the same as a mcdonalds drive through worker makes so the skill level is not that high.. I would never epoxy it