Bondo, seam sealer, and caulk

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I was wondering the other day as I patched rust on my beater pickup what the difference is between seam sealer as applied at the factory and ordinary caulk like you would get at the hardware store.

I'm running "siliconized acrylic" caulk that's 99 cents a tube and presumably a grade worse than the pure silicone that's two or three times the price. I'm patching a rust hole on the lowest part of the b-pillar where it meets the rocker panel on my 94 sonoma: a common spot for a hole. I want to keep water out and also need to seal up any holes exhaust could conceivably enter the passenger compartment in order to pass state inspection.

My stick welder doesn't do sheet metal so I'm drilling holes and using pop rivets. If I were to use body filler I'd have to dimple the rivet heads inward which is complicated and requires lots of mud. When I use that much mud it bubbles, cracks, and falls out. Plus I simply lack the patience.

So my new plant that I enacted on my truck is to simply apply caulk over the rear of the patch panel that applies over the hole and has an inch or two of overlap over good metal. I figure it's better at keeping abrasive spraying water out and doesn't absorb liquid like bondo. Plus the patch panel is already flat and shiny so I don't need to sand it. Just quickly smooth out the "ooze" on the panel line, dry, paint, and I'm done.

Wondering what a hack I am as I don't hear of this technique much. Only has to last a couple years as the frame itself is also getting rusty.
 
i use poly butal caulk on my out door duct work, and that holds up very well and its not very expensive $3.89 a tube when i bought it last week, and it sticks to everything! cleans up with mineral spirits, when you go to the store DONT use my spelling smile!
 
Factory seam sealer would be more like 3M's "5200" marine polysulfide sealer. Much like "Liquid Nails" or "F26". Sure they all have slightly different recipes, but close.

Bob
 
I also paint, and know my glues.
Household caulk can be OK, depending on what you get. You can't paint over most silicon infused caulk.
Proper seam sealer is thick and sticky. It works the best on cars.
 
I can't think of the name of the stuff, but there's a body panel glue. It comes in two tubes and gets mixed. Modern body shops are using it as a substitute for welding.

I'm going to use it on my 68 roadrunner where the quarter meets the outer wheel well housing, that way I won't burn through any coating that will prevent rust around that area. The rest of the quarter will be welded, however. It seals out moisture as well.
 
Most stuff in 2 parts is an epoxy that should be very strong. Thanks for the feedback. My caulk says it's paintable.
 
Aaah, good to know. I still get a warm fuzzy knowing the space between metal layers is sealed off. Will make better effort to ensure no caulk is gooped outside the seam.
 
For internal seams, there is a product called "gutter seam seal" that is very good. I just discovered it, runs around $3-4 dollars a tube and sticks very well but never completely hardens. I keep finding more uses for the stuff.
 
Eljefino, I just resurrected an 88 BMW 528e using over 1000 pop rivets and some sheet metal. I have been refining my technique for about 30 yrs. It is slower than welding but less prep is involved.
 
Egads that's less than an airplane but not by much!
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I sure hope you have a pneumatic riveter or you'll be getting carpal tunnel at that level of production.
 
Heh heh, slow and steady. gloves help. I spent about 10 months on the project , so it wasnt too hard on the hands. Lotsa hammering too.
 
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