Hot Rods Seam sealer

i an finishing floors in my model a coupe.
All the pieces are butt welded and I plan on some sort of undercoat on the outside and sound deadener on the inside.
Does one normally seam seal butt welded floor joints?
Inside and out?
Do you apply it to bare metal or primed metal?
What product would be recommend and how does it get applied normally?
Sorry for all the newbie questions, want to do this once.
Thanks.

 

Good questions that I also would like to know the answers to.
So here's a bump for you!

 

After primer, I’ve always used a sealer or oxide primer.

I have read that it’s no good to use seam sealer on top of etching primer , won’t bond well
And never in bare steel

 

I always seam seal. It fills pinholes and seals the weld area. Lately I've been using POR Patch, a Por 15 product which comes in a tube. I put a thin bead over the seam, smear it with a nitrile glove on and brush it out. Dries in 4-6 hours and is thick enough not to run on a vertical surface. Like it.

 

There are many different kinds of seam sealers. Single application, two part, brushable, self leveling etc. If you are going to use seamsealer, read the directions on the product to see what the recommendations are for substrates.

Having said that, I really don't understand why you would go thru all of the work to butt weld in panels and then apply seam sealer. It defeats the purpose of making an invisible joint. Your primer. undercoat, and sound deadener should seal up any pinholes. If I was planning to apply seam sealer from the start, I would just overlap the panels, spot weld it in and then apply the seam sealer to seal the joint. It would save a lot of time & effort, and visibly look the same when done

 

My metal guy had me use All-Metal to seal up welded joints and a primer or sealer over that.

 

There are some seam sealers that are DTM, but I still prefer to prime first. On exterior panels I like 2 part sealers, but hidden areas the goop in a tube will work.

 

The brushable stuff from wurth is awesome. Is flexible and spreads easy. It will work fine on your model a. I use it a lot in trunks and floorpans as well. Like stated. It will pull up the primer Usually. It’s usually grey in color. Make sure you get acid core brushes. As it will smoke your regular paint brushes. They are usually 1-3 bucks each. You’ll need a few. Also you can paint over it!

 

Weld pin holes closed.
If you need a smooth surface use a bit of body filler.

 

Sand and clean the new floor. New metal usually has oils on them. I prefer an epoxy on bare metal. Then seam seal over the epoxy. I have fixed a lot of rust under seam dealers over the years

 

I have used seam sealer on bare metal welds . Never had a problem with it. It was just seam sealer that I purchased at the parts store in the aisle.

 

So I’m sure you have a normal caulk gun? If so 3M urethane single component seam dealers are approved for direct to metal applications. If you really want it to look nice you can frame of the areas with 3/4 in tape, appply the sealer, brush it or spread it, pull you tape while it’s wet and make it look nice.
It’s never a bad idea to it over a 2 part epoxy primer either

 

Thanks for the prompt and in depth responses. Very helpful info!

 

I don't see any good reason to seam seal a butt weld. if there are pin holes weld them up.

 

My nephew has been the the autobody trade for thirty years. Very anal about his work. Taught me the same trick and likes to use self leveling seam sealer. No one will e really see it but it does make it look so much more professional. If you want original looking spread it on with a trowel!

 

Also, wear gloves. It will stick to your arm hair and hurt coming off if you don’t get to it quick.

 

Be careful during piss breaks.