Technical Strange etching from rust on floorboard?

I wondered if anyone has ever encountered this? Putting in some new carpet and wanted to check the floor boards and seal any minor rust. The pans looked really good, but those lines you see are actually “etched” into the metal. Just deep enough to maybe catch your fingernail. I went ahead and sealed them with por-15 but I’m puzzled how those deep lines came to be? When I pulled out the old sound deadening and insulation it was damp on that side. When I bought this old pickup the heater core was unhooked. I pressure tested it and it leaked, so I put a new one in. My guesses are…
#1) Maybe some type of acid like reaction between the old glue and moisture/antifreeze?
#2) The original pan didn’t have a uniform finish way back when it was built?

 

The 26 T I’m building has some metal that’s etched lightly. It looks like it came off the line like that though.

 

Looks cool

 

The rust worms were crawling around under the carpet.

 

Mine has a face rusted in the side of it

 

That’s some back seat boogie

 

That really does look like a face!

 

Call a priest!!!


But for the original OP my guess would be battery acid or something of the like .

lots of dumb stuff can happen to an old car over the years .

 

Wow. At first glance it looks like you peeled a wet sheet of plastic off of it. But damn, that is really eaten in there really deep, and more shocking is it wasn't a ball of brown rust, it looks damn clean.

I don't know what's up with that.

 

Like @rusty rocket said, kinda looks like it was always there. Strange.

 

One of my other buddies said the same thing.

 

Anthony, is that truck from Turin, Italy by any chance?

 

Nope.
Postal Service somewhere in Florida

 

I kinda thought that too since the pan is in such good shape. Seems odd to me it would “rust” just along those lines.

 

I would say it's from salt water, since you live by the ocean, or if it was ever up north from road salt.

 

Spookie! Bad ground.

 

That’s a good thought, it spent its whole life in Oklahoma. I think they get snow there occasionally.

 

I expect the insulation was in contact everywhere except where the rust happened....so moisture must have been able to only get to where it was not in contact.....

 

that, and maybe related to a 'string' of adhesive used to hold the insulation in place.

 

What year is the truck? Did it possibly have sound deadening material on it that cracked in that pattern, and the pattern is the area that wasn't protected from moisture?

 

My guess it had the old tar type that had dried and cracked. It left the exposed cracks that rusted. As mentioned you don't know the history but someone could have tried to chemically clean it, found that a fail, in removing the rust, or offer a solution to the resulting mess, then went further removing the crap and the tar stuff. Looking you can see grind scratches.
But so what. What you have to ask yourself is what are you going to do about it.

 

I think that might be it.

 

I thought this too definitely.

 

I think so, it had like the old style insulation and then over that was a black almost plastic feeling layer that I’m sure was just dried out.

 

Yes, the original stuff was still intact when I took it out last night. The lines aren’t deep, just enough to catch your thumbnail. But the truck sat undisturbed for 20 years. So all things considered it’s in amazing shape. I don’t think it has any effect on the structural rigidity of the floor. I’d just never seen anything like that in all the old stuff I’ve messed with. I mean it’s under the carpet, but I think I’ll put some seam sealer in those lines just to even it out.

 

Is that a road map of Hazard County?

 

I'm sorry I would have to skim coat that with some filler and block it then use some direct to metal Evercoat 4+1 polyester primer and block it with 150 then apply another coat of primer and wet block it with 400. and paint it. Then 4 coats of base, 3 or 4 coats of clear, 1500 wet and buff it. Lippy

 

possibly cracks in the sound deadening concentrated the liquid to form those lines?

 

You never know what them Duke boys are up to? Hahaha!

 

Road salt wouldn't do that. Road salt would rot the underside out long before it would etch grooves into the top.