seam sealer

[GoMangoBoys]

One area of bodywork where I am totally ignorant is seam sealer.  I have seen that in some cases on cars, there is a sealer between 2 panels and the spot welds are done right through the sealer.  When making repairs, I have never replaced that sealer.  Now we are about to replace the roof skin.  The seams where the roof skin meets the gutter had sealer and that seems like a place where it is really needed.  I am going to replace the spot welds with plug welds since I don't have a spot welder.  Is there a seam sealer that I should put between the panels before I weld them together, or should I just coat the seam after it is welded?
Thanks

[JS29]

@GoMangoBoys After!!!!  Shops now day's panel bond there, They weld the area under the glass front and rear.  Panel bond seals as well, so less chance of a water leak down the sides.  And no welds to grind

[GoMangoBoys]

Thanks.  I have been a bit sceptical about using panel bond.  I have no problem believing that it is awesome in new cars.   I am concerned about the long term adhesion to metal that was once rusty.   Will it fail to adhere over time? I know in 30 years my would will still be good.   I am not arguing against it, I am just concerned that I will trade a long term quality repair for short term convenience.

[JS29]

Unless you can get to and clean up the back side of a weld, you already started the rust process with the heat from welding.  You must have clean metal to start with ether way. 

[GoMangoBoys]

I try to make sure rust is cleaned up well before welding.   Maybe I am just paranoid about something I am unfamiliar with.

[7E-Bodies]

Use a good quality weld through primer on the welded surfaces prior to welding. I use 3M brand in rattle can from my paint supplier. Cashy at $20/can, but we'll worth it. I plug weld also. I also use their seam sealer. If you want, I can get you the exact product numbers when I get home.

Kevin.

[JS29]

What are you using for weld threw primer?  I have been guilty of resisting the new method of things. The bond works well. follow the instructions and you will be surprised, I have used it, and my friend with the big shop in the neighboring city were i live, has been using it for years.  I will admit it dose feel like it's cheating, compared to the weld and grind way of doing it.       

[GoMangoBoys]

This is the weld thru primer that I use.  The Copperweld is easier to weld with, but I think the etching primer might bond better.  With the etching primer, I pray the mating surfaces, then after they are together, I scrape the exposed areas of the joints to expose the metal before I weld.

[GoMangoBoys]

@7E-Bodies   Please tell me what seam sealer you use.  I am on the fence about which way to go and want to consider this option.  Thanks.

[jimynick]

Some points to consider before welding, if I may? JS29 has already spoken about weld-caused corrosion and then there's the grinding and trying to make the ground areas look like a factory job. As for bonding being "iffy". You could always call any of the Big 3 (and most imports as well) and ask them if they think their new vehicles will have a failure "down the road". I can assure you that they don't and as a former sceptic myself (and an old school bodyman), I've become a convert. Not a blind convert mind you, but one who would do what was recommended earlier and put some spots in the corners and bond the rest. If you apply it right, it squishes out slightly and you can tool it to look like an oem sealer, thereby killing 2 birds with one stone and ending with a tighter, more structurally sound and well sealed end product. At the end of the day though, it's your car and your call. Here endeth the sermon. 

[7E-Bodies]

Here's what I use. I believe it's what Cody recommends on his How to Paint a Show Car Finish wrote up. Search out the way to apply it best, as seen on previous threads here.

[70 Challenger Lover]

There is a product I used on my roof rails last year that was amazing. I can't seem to find it but basically, you lay it down in the rails after you're done installing the roof. It lays down flat and smoothes out. Seals everything in and creates a nice clean finish that can be sanded and painted. I'll look around for the tube. I'm going to have to do the roof on my current project and I definitely plan on using this sealer again in the rails.

[GoMangoBoys]

@JS29  @jimynick   Please tell me what panel bond product you are using.
Thanks

[Skid Row]

  2016 E-150 Ford Van "Door Skin" on my company van. I'm not convinced on panel bonding.

[JS29]

@GoMangoBoys 3M8115.