Thread: Panel replacement

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A question for the experts...Is the new glue good for putting panels on, or is welding still the best?? Is mig ok, or should the panels be tigged??? Should a seam be welded full length, or is stitching ok???? Any neat tricks for keeping a panel cool when you're welding it, or just drink coffee and watch it cool down? Thanks for the opinions.

Dave, I've been away from it for a couple years, but I assume you're talking about two part adhesive for bonding panels. e.g. Lord Fusor, 3M, etc.

I know the factories are using these systems on new cars, most of which are unibody. That's a key point, because the entire shell is a stressed member to some degree or other. As such, bond integrity is critical to maintain crash resistence. So, in a word, they work great. Many of the OEM's have, to my knowledge, resisted authorizing wide spread use in the autobody repair arena because of a concern for adherence (pun intended) to proper procedures. At the factory they control the variables, temperature, pressure, bead size, placement, etc., to get repeatable results. It's their opinion that not all repair shops are willing to go to that much effort. The adhesive suppliers, of course, believe they have developed procedures that will allow the repair shop to closely duplicate the factory "performance". I would say you should read the material specification and procedures literature from your preferred adhesive supplier to find out how confident they are in performance, and whether or not you can duplicate their recommended procedures.

We used door skin (non stressed panel) adhesive for years. In fact I insisted on it because of the ancillary values. One, it made for a "quieter" door, two, with a full bead of adhesive around the shell flange there was no opportunity for moisture entrapment. I would hate to see a repair come back in a couple years with rust "dust" showing around the skin flange. We never used the material for larger body panels, mainly due to the OEM warnings. By now the technology may be more advanced, or the experience curve is farther along. If your subject repairs are on the older cars with separate bodies and frames, then I think the opportunities would be more favorable. With the exception of convertibles/roadsters, there really aren't any stressed, exterior panels of a critical nature. Depending on which panel it is, and where your cut line is, theoretically you could attach a complete panel with no welding. Again, follow manufacturer (adhesive) recommendations for proper application. As for patch panels I can speculate, though again, the adhesive company tech department can probably give you better answers. I'm not a big fan of putting in patch panels with the flange method. It's easier for the novice who hasn't developed butt welding skills, but it is also more difficult to reshape (due to double thickness), and is a great place for moisture entrapment. With adhesive, you won't have the heat to distort the panel, and the bead would provide a barrier to moisture incursion. A panel seam (at the cut line) e.g. at the quarter panel to roof sail, should probably still be welded for integrity of the filler base sake.

We used mig welding all the time with acceptable results. Of course we weren't doing concours metal work either. The "old boys" prefer gas welding so they can hammer the bead flat (mig beads are pretty brittle, and don't hammer well, partly a heat thing). Tig is supposed to be better as it is less brittle, and you can control heat, thus distortion of the sheet metal, better. Any method should be acceptable depending on what you're best at. Each guy seems to have his own ability to figure out a way to make whichever method he prefers work for him.

Stitch welding is a starting point. The voids between welds could be a source of "movement" or additional flex, eventually damaging the filler and/or finish on top of it.

Check with your welding supplier for "heat dam" materials. We used to use a blue material that looked kinda like paper mache. I'm sure it was some sort of non-asbestos, organic material. You'd wet it, put it near the weld area, and it stopped the heat migration. It was pretty amazing stuff. Sorry, don't remember what it was called. Otherwise, there's the old wet rag routine. Again, I've seen some be successful with it, and others make a choclate mess causing warpage. Practice, practice, practice.

BTW, most geezers won't believe in the panel adhesive thing, so if you're going to try to get opinions from users in the field, you'll probably need to be talking to the younger guys. Change sometimes comes hard for some.

where would one find such panel adhesive (paint supply store?) and by what name/brand shoudl one look - even a web site link would be helpful.

Dave,
i have quite a bit of hands-on experience with panel adhesives (3M and Fusor mainly) from my former career as a body tech and can tell you they work great for what they were designed for......that is external panels only (no structural panels, i.e. intrusion bars, supports, ect are to be "glued") and dont try to use filler over glued exterior seams (like sail panels)...the glue expands and contract differently from the fillers and you'll end up with cracks along the seam line (per the manufacturer), ya gotta weld those seams! Surface prep is very important, grind the mating surfaces with 80 to 36 grit to give the glue somthing to bite on and clean with a fast evaporating solvent like laquer (sp?)thinner.

The shear tests done by 3M are pretty impressive and i belive the delamination temp is around 600-800 degrees..so if you screw up all you have to do is get out the heat gun and take it off!

So, I should glue on a replacement door panel, and I would be better off welding the rest of the body mods?? To clarify, I am talking some extensive quarter panel and rear end mods on my Ranchero. Any seam that will require filler should be welded because of the different rates of expansion, is that correct?? Hey Streets, if I TIG the panel on, is lead ok over that too??? I quit body work many years ago, but am forced back into it because I can't find anyone to do the work the way I want it done. I guess this is why we are all hot rodders in the first place, huh ?? I really appreciate the input guys, I have a lot of catching up to do on the new body procedures. Thanks much for sharing your knowledge and experience.

Just to clarify the door skin thing for those that may not be familiar with it. You still want to "fold" the edges over the inner shell flange even though you've bonded the face. In other words, a normal skin replacement except for adhesive instead of welding.

Sounds like you have the rest of the idea. You could still bond the quarters on, just weld the mating seam to the sail. (Sorry if that wasn't clear in my original post.) You could lead over TIG, it doesn't know the difference, but, unless you're going for bragging rights, polyester fill would work just as well.

I know what you mean about not finding someone to do it your way. Twenty five years ago I tackled my first metal straightening for the same reason. I had a '51 Hornet that some kids had used the roof for a trampoline when it was laying in a field. The rest of the car was so sweet, I had to save it. Great learning experience hammer and dollying all those little ripples.

The ones who really knew how to do body and fender work on REAL cars and trucks in this neck of the woods went and got old and retired !!!!...I too have had to learn how to do the work myself...I don't try to build for show to someone else..Just for ME...I take my time and my old Chev trucks look pretty damn good...I just love to own em..drive em..repair em...Al...

Thanks much for all the help, guys. The Ranchero project is coming along just fine. Will post some pics when it is in primer. BTW, I use epoxy primer now, but when all the tin work and welding are done and ground, what is the best "1st coat" to put over the work before the smoothing and blocking begins??? Thanks again for all the help.

Dave
I do all the block sanding with lacquer based primer surfacer till I'm satisfied with the results then I coat everything with epoxy primer for the final block sanding. I have been using bondo for a long time and it doesn't crack when done right unless you crash it. I use the fiberglas reinforced filler over seams and then a finish coat of regular filler to get a smooth finish. I don't put filler over primer or paint. It adheres best to bare metal.
AL

Dave,
Epoxy primers are not considered a filling primer, its more of a sealer then anything. (isocyanate free)
Primer Surfacer is a filling primer ( and used for filling & blocking to make smooth panels)which have isocyanates,and most refer to these as K2 primers .

This is what I would do if it were me:
1: Strip down to bare steel.
2: Spray DP 40(graygreen), Dp48( White), Dp50 (Gray),DP74 (Red)or DP90 ( Balck) This is PPG's Epoxy primer.
3: do my bondo work over the DP sealer, and yes it is highly reccomended to do this by PPG's people!better adhesion of the bondo.
4: when all body work is done , Spray 4 coats of K-36 or NCP 271
Primer Surfacer.( another PPG product)
5: Block sand with 180-220( and these primers sand real nice)
6: Spray 4 more coats of K-36 or NCP 271 & block out with 400 grit.
7: Then panel should be ready for paint!!

I would stay away from Lacquer products as they are 25 years behind times & the Paint industry has Improved greatly since then.
These products dont have the shrinking And soaking up like lacquers do, plus they have a tad bit of flex to them.
remember the old days of lacquer and all the little cracks in the paint , this is the reason why, metal expands & contracts , lacquer doesnt expand & contract.

Do it right the first time .

SprayTech

I would tig weld your pannels on they have less heat distortion then a torch and you can hammer weld. which means weld a 1/4 inch then hold the dolly on the back side of the weld and hammer on the fornt to strech the shrunken weld. if you can not get to the back of the weld you can use a nail gun to put a nail on the weld and use a slide hammer or a rivit gun with a cone shap puller on it to bring the shrunken weld back up. then you can fille off the weld and posible metal finish your pannel.If you are going to use lead or filler I would put it on 24 or 36 grit grinded bare metal the put the yellow rust preventer primer on It stikes to bare metal the best then put your filler primer on for the monior imperfections

Thanks for all the help, guys. Seems the more questions I ask, the smarter I get!!!!!! Someone should start a thread that would give a cumulative total of CHR members combined years of experience doin hot rods !!!!!