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I'm part of a college student engineering organization and we were just able to get a 2005 Ford Explorer for free. It's in good condition except for the roof which has rusted pretty badly due to years of not being used often and rain pooling on top.

We are able to store it under cover and aren't too worried about looks or absolute best practices, but we would like to keep the interior safe from possible water damage in the future and prevent anything from getting too bad on the roof.

What is the best way to cheaply slow the spread, seal, or fix a roof like this? I've heard coating it with flex seal will work well, but my question is how long will that last? I've included photos below.

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3 Answers 3

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Does not look too bad, possibly not through-rust. Sand the roof to bare metal and use a rust-stop product, such as POR-15, following the instructions. If desired, sand with fine sandpaper after and cover with a bedliner product. Those two combined should pretect it for the next decade.

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    Vera, if you use POR-15, you must cover it with another product, or UV from sunlight will degrade it within a matter of months. A bedliner product such as this answer suggests would work fine as protection from UV, as would car paint or any other paintable product intended for use on a car body.
    – MTA
    Sep 13, 2023 at 13:01
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If you leave rust around, it will almost certainly spread.

I have personally repaired roofs that appeared to be in similar condition as your team vehicle's roof, and worse (impossible to know the exact condition of your roof until you remove all the rust).

What I've done to repair such roofs:

  1. Grind, then sand, the roof down to bare metal. Expect this to take 5 times as long and 10 times more effort than you originally anticipate!
  2. Apply Bondo body fill to any areas that require filling. Allow to fully dry.
  3. Sand the Bondo.
  4. Wash the roof and dry it super well.
  5. Use tack cloth to remove anything that washing didn't remove. You don't want any tiny metal fragments left behind from step 1.
  6. Apply several layers of Flex Seal to the roof. I use the spray can variety. I typically apply 3-5 coats. Make sure you hit the corners especially hard.

That's it.

I have vehicle roofs that show no sign of problems after more than half a decade after performing the above steps. And some of those vehicles are older than your vehicle.

Good luck!

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  • You have to put some kind of sealer or something to stop the spread of rust. Just grinding/sanding will not get rid of all of the rust. Maybe even soaking it in Evaporust or vinegar to kill the rust would be needed to stop it, then do as you suggest. Sep 13, 2023 at 13:56
  • @Pᴀᴜʟsᴛᴇʀ2 On expensive vehicles, I would definitely recommend doing exactly as you mention (applying some sort of dedicated rust inhibitor and sealant). For inexpensive vehicles, I have found Flex Seal to be sufficient. I think, perhaps, Flex Seal forms a sufficient bond/barrier to prevent the rust from reappearing, but I honestly don't know because I've never needed to remove Flex Seal after I've applied it because it's always worked so well. I always make sure all visible rust has been removed before applying it. Sep 14, 2023 at 5:27
  • @RockPaperLz-MaskitorCasket do you ever paint over the flex seal? Or do you usually keep it exposed. How does the flex seal visually look? Do you cover the whole roof or just the rusted part?
    – Vera Fodor
    Sep 14, 2023 at 13:09
  • Good questions. I never paint over the flex seal. I don't think it would look good, because it leaves a rough finish. I always leave it exposed. I think it looks great. I use the black Flex Seal. It looks similar to a truck bedliner, except the finish is matte. I cover the whole roof with Flex Seal. Sep 14, 2023 at 13:19
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I've used Permatex Rust treatment in the past, with excellent results. It lasts about one year before you have to re-coat. If you prime and paint after coating, it will last indefinitely. No need to sand.

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