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Old 06-26-2019, 09:37 AM   #1
shifty
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How to handle - Floor surface rust

Shy of replacing the foam gasket on the fresh air intake of my GMT400, I fixed all water leaks in my truck. Now I need to clean up the damage of PO ignoring them.

I'm installing tar-like adhesive-backed sound deadening mat (Dynamat) on my cab floor, but I want to deal with some rust first.

What's the best way to handle these bubbled up and surface-rusted spots before installing the mat?

Sand, self-etch prime or rust bullet/POR15/similar rust sealer? Paint over that?

How long should I wait after treating and paint before installing the mat?

Any "aha!" things I should know about, like the rust at the seam sealer up front?

Feedback is appreciated. Looking to get this started soon.

Pics, hopefully the forum doesn't make them too "potato" quality, if it does, I'll post better close-ups later today. (edit: Yup, it potato'd them out, I'll post better hi-res pics in a few hours)
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Old 06-26-2019, 02:16 PM   #2
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Re: How to handle - Floor surface rust

I'd take a sanding disc and clean the spots to bare shiny metal....then put epoxy primer on those spots..
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Old 06-26-2019, 06:09 PM   #3
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Re: How to handle - Floor surface rust

Here we go, here's a better shot. Especially along the body seams.







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Old 07-05-2019, 10:27 AM   #4
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Re: How to handle - Floor surface rust

Your floor has been painted previously without using epoxy primer. Epoxy primer prevents rust "creep" which is exactly what's happening to your truck.

Because we know there's no epoxy primer, I'd reccomend stripping all loose paint to bright metal and apply epoxy primer as Mongo suggested. If you are more determined and enthusiastic, you might consider stripping all coating on the floor and then apply an epoxy over the entire area.

Once the epoxy is dry in 24 hours, you can apply paint or just put the Dynamat over the epoxy.

If chose any product other than "epoxy primer" you are wasting your time and money as there's no substitutes for what epoxy primer does.
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Old 07-05-2019, 11:20 AM   #5
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Re: How to handle - Floor surface rust

I'm obviously not an auto body expert but I can say these Polycarbide Abrasive Wheels from HF work really well for removing the rust and surrounding paint without removing as much metal as say 40 grit.

I ended up buying one of HF's $12 angle grinders to use with these wheels as my good 15 amp angle grinder is too powerful - their cheap one (item #60625) is only 4.3 amp - also I've heard the dust from these disks is not good for the angle grinder, so for $12 it is hard to go wrong.

The wheels come is 4-1/2", 4", 3" and 2" and are rated to 11,000 rpm.

The 4-1/2" wouldn't fit on the 4-1/2 angle grinder as it hits the guard; but the 4" one does fit.

Those welds are interesting in the photos - are those done by welding robots in the GM factory? They are good looking welds.
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Old 07-05-2019, 01:11 PM   #6
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Re: How to handle - Floor surface rust

Gromit....that's seam sealer....not welds
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Old 07-05-2019, 06:31 PM   #7
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Re: How to handle - Floor surface rust

Quote:
Originally Posted by Foot Stomper View Post
Your floor has been painted previously without using epoxy primer. Epoxy primer prevents rust "creep" which is exactly what's happening to your truck.
Awesome. Paint is factory, I guess GM didn't use epoxy primer on body panels in '98! I figured the white/grey was the factory primer. Truck's never been in an accident, repainted, nor carpet replaced.

I've got all the tools to take the paint up, now I know what to use. Only other concern is whether I need to do anything special at the body seams, you can see the rust rolls right under the seam sealer in a few spots.

For whatever it's worth... This rust is courtesy of the massback under the carpet staying saturated for years under the previous owner's watch (cowl/3rd brake light water leaks).

It only dried out after I got the truck, removed 3 of 4 seats, folded up the carpet and put it in the blaring sun with the windows down all day for several weeks. Recently pulled the carpet to see how bad it was ... yeah.
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Old 07-05-2019, 07:05 PM   #8
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Re: How to handle - Floor surface rust

I'd remove the seam sealer...clean it all up ,epoxy it,and reseal it
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Old 07-10-2019, 02:53 PM   #9
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Re: How to handle - Floor surface rust

Any tips on how they get that awesome TIG welded look on the seam sealer?
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Old 07-10-2019, 03:01 PM   #10
mongocanfly
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Re: How to handle - Floor surface rust

https://m.youtube.com/watch?v=5BEVI5FCYd4
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Old 07-10-2019, 05:02 PM   #11
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Re: How to handle - Floor surface rust

Quote:
Originally Posted by shifty View Post
Any tips on how they get that awesome TIG welded look on the seam sealer?
That's a cool video Greg shared.
If you want the sealer to look like that, That video really helps.

Here is my opinion.
I was employed at an automotive plant for 18 years.
I don't care to mention which one.
Four of those years I was in
the part of the plant that
put the sealer on the cars.

The reason it looked like that is the sealer gun was turned up high
so that it would cover the seam fast. The floor seams was less critical
for appearance (because they get covered up) than the door seams or seams that are visible.
The seams that are visible get squeegeed smooth like in the video on the second seam (but with no air ) .

(My Suggestion If you smooth Your sealer out it will get down in the seam better
and be flat on top so it will be less likely to hold water in the future.

Working in the sealer area I learned why there was sealer in area's
that might not require sealer.
Reason #1 : If your friend working down the assembly line put's there
hand in the same spot on each car( to brace their-self)
They will get messy
Reason #2 : If you put a Big Pile of sealer where they sit in
the car (to do there job) and they don't see it






.
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Old 07-11-2019, 07:02 PM   #12
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Re: How to handle - Floor surface rust

My thinking is, the rust started in those seams under the sealer...clean that seam seal out, spray the seams with ospho so it will seep in the joint where you can’t clean out and then spray with epoxy...reapply the seam sealer.
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