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Thread: POR-15 Surface Prep Question

  1. #1
    Senior Member Traveller's Avatar
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    POR-15 Surface Prep Question

    Hi All. I have a quick (and likely stupid) question...

    I've never used POR15 before, but ordered the kit from amazon which arrives today. I see that it includes some kind of metal prep / etching primer as part of the kit. I plan on using this to paint the cast section of the IRS differential tonight. My question is that the differential (bought from FFR) came painted from the factory. I assume I need to strip that paint off to get the POR products to adhere properly. Is that correct?

    Also, is there a recommended brand of clear topcoat? I see POR makes one, but I did not purchase that.

    Thanks,
    Jason
    MK4 Complete Kit #9673 | Ordered: 08/07/2019 | Pickup: 08/24/2019
    Gen 2 Coyote, TKO600, IRS, Power Steering, 18" Halibrands, Kirkey Vintage Race Seats, Gas-N Headers and Pipes
    Build Thread: https://thefactoryfiveforum.com/show...IRS-Build-9673

  2. #2
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    I'm not going to be able to help too much, but I thought I'd chime in.

    First, please don't apologize for asking questions. We've all learned as we went along. Questions are good.

    Building this car was my first time with POR-15 too. Now I use it for a lot of things. I purchased the spray can, and just spray it on top of whatever I'm painting. I haven't used the primer. My rear was from a junk yard (Not IRS) and it had a lot of surface rust. I cleaned the entire rear end with brake cleaner, and sprayed several coats of the POR-15 on it, and it's still on there just fine. But mine really needed it, and your differential has been newly painted (if I understand correctly). It doesn't come in contact with anything during it's life (hopefully), so I wonder if you need to paint it again. If you're happy with the appearance of the painted differential and you want to put clear on top of it, just add several coats of POR-15 clear coat on top of the already painted item.

    HTH
    Last edited by DadofThree; 09-16-2019 at 03:09 PM.
    Dave
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    Senior Member edwardb's Avatar
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    First I've heard of the IRS differential received painted. Are you sure? Would be interested in a picture if you could post one. Whether the iron case (which is the one I believe FF supplies) or the aluminum case, every one I've seen and used was unfinished. The iron case version turns rust orange almost immediately, which is the reason many of us paint it. If yours is already painted, maybe don't even mess with it.
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  4. #4
    Papa's Avatar
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    POR means Paint Over Rust. Wire brush the loose stuff of whatever you plan to coat with POR-15 and make sure there isn't any grease, oil, silicone, etc. and brush or spray the stuff on. It's very forgiving and as long as you don't try to recoat it when it's tacky, will self-level to a nice smooth finish. You should use top-coat if the area you are treating will be exposed to sunlight as POR-15 has no UV protection and will fade. I've never used primer or top coat and everything still looks like it did the day I applied it.

    P.S. wear gloves! If you get this stuff on your skin, plan to wear it for a couple of weeks!
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    doddmoore's Avatar
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    POR is for Paint over rust as others have said. I am currently using it and have found if it does not have rust on it, as mine does not, the surface should be cleaned really well then scuffed really well. It will need something to adhere to and the scuffing gives it better adhesion. I tested with the scuffing and without and the scuffed was MUCH better.
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  6. #6
    Senior Member Traveller's Avatar
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    Quote Originally Posted by edwardb View Post
    First I've heard of the IRS differential received painted. Are you sure? Would be interested in a picture if you could post one. Whether the iron case (which is the one I believe FF supplies) or the aluminum case, every one I've seen and used was unfinished. The iron case version turns rust orange almost immediately, which is the reason many of us paint it. If yours is already painted, maybe don't even mess with it.
    Pretty sure... Here ya go:
    MK4 Complete Kit #9673 | Ordered: 08/07/2019 | Pickup: 08/24/2019
    Gen 2 Coyote, TKO600, IRS, Power Steering, 18" Halibrands, Kirkey Vintage Race Seats, Gas-N Headers and Pipes
    Build Thread: https://thefactoryfiveforum.com/show...IRS-Build-9673

  7. #7
    Papa's Avatar
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    That looks like undercoating. I'd probably just install it as is and call it done.
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    Senior Member edwardb's Avatar
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    Agreed, that's a factory coating. Evidenced partly by the factory handwriting on the case. Same as on previous NIB versions. Interesting change from our friends at Ford. Like I said before, the main reason most of us were painting them was to hide the orange rust that starts the day after they're built. I'd be inclined to leave it as is as well.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
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  11. #9
    Senior Member VAHokie's Avatar
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    Great timing on this post as I was planning to POR15 a few things this weekend including the diff. Mine came with the undercoating as well and I had the same question, so thanks for beating me to the punch! Would duplicolor's engine enamel gloss clear be sufficient or should I look to something else to seal it up?
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  12. #10
    Senior Member DavidW's Avatar
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    This would've helped but looks like some insight has eliminated the need.

    FYI thinning out the second coat of POR 15 really makes a nice smooth finish coat, similar to a powder coat finish.

    https://www.por15.com/POR-15-Technic...ion_ep_62.html

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  14. #11
    Senior Member KenWilkinson's Avatar
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    Another similar product. Also in silver

    http://www.magnetpaints.com/underbody.asp

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  16. #12

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    PREP ! That's funny. Once you use it you will find that it sticks to EVERYTHING ! Were rubber gloves, put down cardboard, take off your shoes before you go in the house.....etc.....etc....etc...da bat

  17. #13
    Senior Member Traveller's Avatar
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    I took everyones advice and left the undercoat on it. I cleaned it up with some acetone and hit it with some clear coat (the duplicolor ceramic that you mentioned) and it looks great!

    Thanks all.

    Quote Originally Posted by VAHokie View Post
    Great timing on this post as I was planning to POR15 a few things this weekend including the diff. Mine came with the undercoating as well and I had the same question, so thanks for beating me to the punch! Would duplicolor's engine enamel gloss clear be sufficient or should I look to something else to seal it up?
    Last edited by Traveller; 09-17-2019 at 09:02 PM.
    MK4 Complete Kit #9673 | Ordered: 08/07/2019 | Pickup: 08/24/2019
    Gen 2 Coyote, TKO600, IRS, Power Steering, 18" Halibrands, Kirkey Vintage Race Seats, Gas-N Headers and Pipes
    Build Thread: https://thefactoryfiveforum.com/show...IRS-Build-9673

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  19. #14
    Senior Member Traveller's Avatar
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    Love it... Looks like I wont be using the POR15 this time, but I am anxious to use this stuff.
    Quote Originally Posted by j.miller View Post
    PREP ! That's funny. Once you use it you will find that it sticks to EVERYTHING ! Were rubber gloves, put down cardboard, take off your shoes before you go in the house.....etc.....etc....etc...da bat
    MK4 Complete Kit #9673 | Ordered: 08/07/2019 | Pickup: 08/24/2019
    Gen 2 Coyote, TKO600, IRS, Power Steering, 18" Halibrands, Kirkey Vintage Race Seats, Gas-N Headers and Pipes
    Build Thread: https://thefactoryfiveforum.com/show...IRS-Build-9673

  20. #15
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    The Jeep frame that I painted with POR15 was sandblasted with no other prep and it still looks great. I did top coat on any surface that saw direct sun.

  21. #16
    Senior Member GTBradley's Avatar
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    Mine was the same, I just clear coated it and moved on.

    Bradley

    Build thread - Mk4, Coyote, IRS, Wilwood brakes, old-style soft top and accessories.

    The distance between "finished" and finished is literally infinite.

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