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Thread: Surface floor rust (outside), what to do?

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    Default Surface floor rust (outside), what to do?

    Hi guys,

    I've been under my z today and found some external surface rust. I know it's only external because i pulled the carpet up and their is no rust inside.

    I don't have the time or money to completely strip the undercoating underneath, so i'm wondering if i can scrape the immediate undercoating around the rust off, scuf the rust up, and coat it with por 15.

    Do you guys think this will be a good fix? That will stop the rust from going any further correct? Let me know what you guys think.

    Thanks,
    Jay

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    Biafra for President e_racer1999's Avatar
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    por is easy fix? yes. will it guarantee that the floor won't rust out? no. your best bet is to strip the undercoating (no matter how much that's gonna suck) and get all of it (if there is more).
    Jason King
    6/72 240Z / HLS30 89646 (Yellow)
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    Quote Originally Posted by xray View Post
    As unfortunate as it may be, if you want to vintage race, go Euro....If you want to race for real, stick with the Z!

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    Jason,

    So you're saying that the por 15 will stop the rust where i coat it, but it will rust in other places, or that it will rust anyway even with the por 15?

    If i striped the whole floor of undercoating, i should por 15 the whole thing?

    Thanks,
    Jay

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    In order for POR to do ANYTHING for you, you MUST strip the metal of ANY AND ALL PAINT. POR must be in direct contact with the metal. You should read up on how POR must be applied before considering the use of it. The metal must be PROPERLY prepared for the application of POR or you will be wasting your time and money.

    There are many threads on this. Use the search function to find them.

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    Actually only one thread on what i wanted to do and i read it. And i was not happy with it's contents, which is why i posted this question. But thanks for the search concern...

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    Registered User Schev's Avatar
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    You said you lifter up the carpet to check if there was rust there. Does youre car not have the tar paper linging on the floor? If you did not remove it, that should be there covering up the metal
    '73 240Z - HLS30-171979 *Under Construction*
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    Biafra for President e_racer1999's Avatar
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    ^that's true.... the tar might be (and probably is) painted body color, so it may appear as though you are looking at the metal...


    what i am referring to by saying that it will rust in other places is murphy's law of rust: if there is rust in one spot, there's rust somewhere else.
    Jason King
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    Quote Originally Posted by xray View Post
    As unfortunate as it may be, if you want to vintage race, go Euro....If you want to race for real, stick with the Z!

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    Quote Originally Posted by Jayru
    Actually only one thread on what i wanted to do and i read it. And i was not happy with it's contents, which is why i posted this question. But thanks for the search concern...

    If all you found was one thread on the application of POR, you aren't using good search terms. POR15 application to Floorpans has been discussed literally dozens of times.

    What specific questions do you have?

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    Quote Originally Posted by Bambikiller240
    POR15 application to Floorpans has been discussed literally dozens of times.
    I'm sorry Carl, your wrong. We have not discussed this dozens of times. I think it's been discussed hundreds of times.
    The 1973 240Z 165540 Slightly modified. L28, 5sp, cam, headers, MSD 6AL, power windows, power door locks, leather seats, custom this and custom that.

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    (Ten Charecters)

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    Quote Originally Posted by Bambikiller240
    If all you found was one thread on the application of POR, you aren't using good search terms. POR15 application to Floorpans has been discussed literally dozens of times.

    What specific questions do you have?
    My specific questions:

    1) Is it ok to scrape the undercoating (and paint) off the visible rust and coat it with por 15. then lightly undercoat the (por) spots to protect the surrounding non rusted, non por'ed area. Would that fix the problem in those areas?

    2) if it is starting to rust through (good point about the tar paper Schevets i didn't even think about that ) Then only treating the underside would not stop the rust? Or would the por 15 attack the rust as a whole, chemically chainging it on the other side (inside the floorboard) as well (even though it hasen't been physically painted on the inside)?

    Specific enough?

    I still think it's just surface rust, i guess i'll know when i hit those spots with a sander/grinder. I don't want to go through the hassle of striping the tar paper if it's not all the the way through.

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    Quote Originally Posted by Jayru
    My specific questions:

    1) Is it ok to scrape the undercoating (and paint) off the visible rust and coat it with por 15. then lightly undercoat the (por) spots to protect the surrounding non rusted, non por'ed area. Would that fix the problem in those areas?
    POR will only protect metal that it is direct contact with. Any metal that you strip and is not prepared properly and treated with POR will be subject to potential rust. Undercoat will not protect the "surrounding non-por'ed area" from developing rust. (that's how the rust you want to treat got there)



    Quote Originally Posted by Jayru
    2) if it is starting to rust through (good point about the tar paper Schevets i didn't even think about that ) Then only treating the underside would not stop the rust? Or would the por 15 attack the rust as a whole, chemically chainging it on the other side (inside the floorboard) as well (even though it hasen't been physically painted on the inside)?.
    POR will stop rust that it is in direct contact with. If the metal is rusted through and you don't treat both sides of the panel, the rust will continue on the un- por'ed side, thus you won't have accomplished much.

    PS: It is VERY COMMON for there to be rust under the tar-mat. What looks like minor surface rust under the mat often turns out to be significant rust. (personal experience talking here)

    The logical time to remove the tar-mat is when you see ANY rust on that side of the panel (in other words, before it has ruined the floorpan so that it must be replaced)

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    Why would non rusted (floor pan) sheet metal sprayed with undercoating be prone to rust? Is the metal in these cars just that bad? I'm assuming the 33 yr old undercoating was crap, but i would think the newer stuff would lock out moisture? It would kind of seem pointless to sell undercoating if it didn't protect the metal no? That's what it's made for.

    Not implying anything, just asking.

    How do newer cars avoid this problem? There undercoated no?

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    Quote Originally Posted by Jayru
    Why would non rusted (floor pan) sheet metal sprayed with undercoating be prone to rust? Is the metal in these cars just that bad? I'm assuming the 33 yr old undercoating was crap, but i would think the newer stuff would lock out moisture? It would kind of seem pointless to sell undercoating if it didn't protect the metal no? That's what it's made for.

    Not implying anything, just asking.

    How do newer cars avoid this problem? There undercoated no?
    First, undercoating is not a 'Rust Proofer".

    Second, Undercoating get's damaged by the elements. Rocks, Road Salt, Chemicals, etc which allows moisture etc to come in direct contact with the metal and traps it there.

    Third, the metal on these cars is thinner than modern cars, that's why these cars are light. Also the metal was not well treated for corrosion resistance

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    If I may intrude....

    Carl is spot on. He should be--he's discussed this loads of times.

    Undercoating is mainly there to deaden road noise and provide some thermal insulation. Oh, yeah--since it is porous it also does a heck of a job keeping moisture up against the poorly-prepped sheet metal of the floorpans. So, the "tip of the iceberg" is very true to form on these cars.

    Take off the tar crap, I suggest heat gun and paint scraper, but it sounds like dry ice also works from other folk's impressions. I then took a small skinny screwdriver and jabbed it into the floor pan, "mining" for rust. I found it along the front firewall, drain plugs, seat mounts and along the rearward weld line. Not much, but the pock-marked looking pinhole type problems. All of this was covered by the tar insulation, giving the intial impression of being "rust free." "Rust free" and "Z" rarely go in the same sentence!

    Grind away. Wear a mask. When everything around you turns dusty-orange, you may have had enough fun with the grinder. Vacuum, rinse, then scrub it down with Marine Clean to get the last bits of grease and grime off. Rinse again and allow to dry. Since the bulk of my pans were pretty solid, I used Metal Ready to get the good metal prepped. (POR Inc. states you don't need to use MR if only applying to rusted areas.) Rinse again. Apply the POR in multiple thin coats according to the directions. Cover the floor pans entirely, you will thank yourself later.

    Work in a well-vented area. Wear a mask. Wear gloves. All those kind of things.

    Hope this helps.

    X

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    In addition to the previous advice I found that a wet/dry vac is very useful when working on the inside. Several of the POR15 steps require rinsing with water and a wet /dry vacuum will get most of it out in a hurry. There's also a lot of other debris that comes out with it. I know that this thread was started talking about the underside of the floor pans but to do it right you really have to treat it on both sides. If there's rust at all under the undercoating there's going to be rust under the tar mat.
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