Can anyone help me figure out the appropriate replacement for this sealer. It is different from the brushed on seam sealer in the engine bay and the spray type used throughout the body.

This product is definitely a no sag formula but it is black and not beige or white like elsewhere. And most notably, it’s hard and brittle vs soft and pliable.

Edit: it also is porous, which I don’t think is ideal…

I used Wurth seam sealer but have no concern for originality.

Nor do I particularly. Original experience definitely, but not outdated products. My concerns is more about function. After removing one side, I’m thinking this was meant to be an NVH foam. It looks like the same product between the welded seams.

Does that make sense?

No it’s a Bitumen based sealer of some sort. Agree it does have some air bubbles but it is not a foam. It is brittle and chips right out easily (mine did).

Definitely not NVH Material in a modern sense.

I suspect it was simply cheaper material to use than the brush sealer used in engine compartment and other places that would see enough heat to soften Bitumen. Probably pumped from bulk and picked up air when pumped. Would be cheaper to apply than the beige rubber based seam sealer used elsewhere.

I don’t know if you have a sealer gun. I used the Wurth seam sealer gun and just used the nozzle tip to get it up in the corner rather than spraying it. Basically a pneumatic caulk gun for their sealer.

Ok, Copy all. Now that I’ve got mine all chipped and wire brushed out, I agree it wasn’t applied with any intentionality. I bought a pneumatic caulking gun, but I’m not ready to spring for a spray sealer gun… too expensive for such a specific tool. I did see a 3M video during my evening youtubing that showed a technique to apply seam sealer and then use an air nozzle to spread and push it deeper into crevices.

I plan to spray in some acid etch primer and then use that trick with my seam sealer that is also suitable for DTM contact.

As always, thanks for the help!

I was just about to order some
ACDelco GM Original Equipment 10-2013 Body Joint and Seam Filler Compound - 10.1 oz
Any reason not to use that?

Is anyone using silicone for underbody sealer? not original but grabs, holds and flexes for many years

but it does cure "solid" in the sense that its not tacky.
that can make it leave the surface even though you can barely detect that.
water can be drawn under that surface between silicone and metal.
making a rust trap?

the butyl based sealants are better in that regard.
they don't completely cure hard on the interior.
they can develop cracks but its usually in the top surface and usually due to exposure to direct sunlight and UV.

have seen a huge amount of silicon sealant failures on roofs here.
roofing plumbers love it.
causes endless capilliary leaks.
its not as flexible as it looks long term.

i'd be hesitant about it.

i used a butyl based soft sealant on the falcon ute where they had used a soft sealant for screw on panels etc at the factory. and the body seam sealant (the hard stuff) that i had to redo i did with the wurth seam sealant. did it by gun and finger method. no silicone anywhere.

I’ve determined that the sealant pictured is the same as the sealer used between the spot welded panels. Both instances I’ve found of that sealer were hard, brittle, and slightly aerated. I’ll be going with a high solids 3M urethane for all uses on this project. 3M also makes a rubber based high solids sealer, but I think urethane will weather a bit better especially since it’s become the standard base material choice for windshield sealant for decades now.

For application I’m going to try multiple passes and blowing the sealer in with an air nozzle after the first pass to ensure I’m not leaving any cavities. If that doesn’t work, I’ll probably abort and spend the money on a sprayable seam sealer setup like superkhawk996 uses.

Disagree, silicone sealants are far better in virtually every regard than butyl. Most failures are due to improper preparation. I am sure all silicone sealants are not equal, Dow Corning is the gold standard.

Also far superior to any urethane. If in doubt, do your research

Silicone is an abomination to paint. God help the next guy that tries to paint anything after silicone has touched it.

Silicone has no place in the autobody industry. If you want endless paint issues use it.

This is an Autobody based urothane applied prior to the installation of the sill. The sealer is squeezed out ro form a bead.

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We have been using Dow Corning 756 for many years as it's a paintable silicone. Far superior to any other sealant, bar none

Wurth SKS with their special application gun

As a sealant for glazing sure

As a body sealer for automotive application - no.

From Dow technical manual
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If serious about using this - better talk to your paint supplier about comparability.

Phil,
Is there anything you are not on top of? We have 756 always on hand, and for undercarriage work it is my go to. In 50 years I will be 120 y/o

Thanks for the tech info as always

It’s not that I’m on top of everything but more so that I’ve been around automotive manufacturing most of my adult life.

Silicone and silicone compounds are a no-go around the body line and plant paint shops. So much so that those that work in them are basically forbidden from using skin care and makeup products that contain silicone compounds as an ingredient. A contaminated paint line is a manufacturing nightmare.

Likewise, my first paint job ran into issues with fish-eyes because someone had used a silicone based paint care product and I didn’t know and didn’t get it prepped / cleaned off properly. I got to do that paint job all over again and got to strip it to bare metal to solve the problem.

Not trying to be hyper-critical if you’ve used it with success. However, that would be an exception to the general rule that silicone products and automotive paint are not compatible and others should be aware of that when there are trusted products that were developed to be used with automotive paint.

@930cabman

Agreed, almost 100%, fish eyes can be often near impossible to be rid of and I would never consider using any silicone near any finish paint.

But for sealing and flexibility I have had nothing but success with silicones (Dow Corning)

TBH, I really appreciate the debate on this and always love it when superhawk996 gives no fee consultation. So here’s where I’m at, I’ll be coating the underbody and engine bay with 3M Dyna-Pro
It’s a rubber based product and I think it might be worth a test to see how it gets along with a silicone product like the dow product we’re talking about.

My only concern is how well the sealant would bond to bare metal vs painted/primed.

I’ve chosen the 3M systems in order to ensure compatibility and I really don’t want to experiment unless I’m confident in a distinct advantage.

very interesting conversation.

i'm with @Superhawk996 on silicone has no place near doing anything with cars.
.......and paint.

at a micro level not only does the paint not take to it (leading to other potential catastrophes) - but the edge between where paint ultimately finishes (long term) and where the silicone starts is your weak point for moisture to enter the system.
silicone sure likes sticking to glass. it bonds beautifully to it. but as i noted above, down the track its adhesion to metal long term has a question mark on it for me.
having seen so many failures after fairly short service life. admittedly it was exposed to UV (fairly extreme and hostile) and a lot of temp movement due to thermal expansion and contraction.

polyurethane is an interesting substance.
these days its falling out of favour in my industry down here. construction industry.
for long term environmental impacts i guess and because ultimately its totally unrecycleable, can't really be turned into anything else and hangs around in the environment for a long time. strangely its all swinging back to butyl based sealants, older tech but i guess with improved formulations and performance.
germany has been leading the charge on this for some time and is out to basically eliminate polyurethane in all its forms out of construction.
its beginning to gain momentum down here too.

but that does not mean its not applicable to the sealant job @VanB is doing in practical terms.

i think that @Superhawk996 has it right though. you want a sealant you can paint over so that the paint surface is continuous and does not break down where it crosses the line between metal and sealant. if it does that is where your rust will start all over again.

Wurth (or SEM) seam sealer - designed for use on bare metal or over painted surfaces. Takes finish paint like a champ. Tried and true. Available in either rubber or urethane.

Just saying

In all seriousness I’d assume 3M is very similar. You’ve got to wonder how many suppliers there really are. Probably one and they just stuff it in different branded tubes.

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LOL I still remember when that episode was new… and when the simpsons was funny. Hell, wonki was probably half American back then!

So, I have this 3M Urethane seam sealer but I am now considering the more old school rubber based 3M Dynatron for the underbody and engine bay since it will be top coated with the rubber based undercoating.

Then I’ll use the urethane for locations that will get paint as the top coat.

i was

i was watching the simpsons in chicago when it first came out.

dead set it was one of the funniest things i had ever seen.

back then i did not conform to aussie stupidity when it came to my friends the yanks.
they have the best sense of humour out there. you just have to get it.

i was at a comedy club in chicago when bill hicks did his "meltdown".
i could barely contain myself with the laughter.

the simpsons were red hot when they were fresh.

american working classs = australian working class.
same people, just speak a different language. still understand each other but!