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Thread: which first, primer or filler?

  1. #1
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    which first, primer or filler?

    I've got a section of bare steel on the truck, it needs a skim of filler.

    I've always primered then filled, as I'm paranoid about it rusting under the filler.
    I've read that others fill then prime.

    What's the right way to do it?

  2. #2
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    I fill them prime but never wet and dry filler always use production paper.

  3. #3
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    Quote Originally Posted by mitty85 View Post
    I fill them prime but never wet and dry filler always use production paper.
    +1

    If the metal is clean before the filler is applied, then sealed with paint, there is no way for the metal to oxidise. Filler also adheres to the metal better than paint and you will get a better feather edge.

  4. #4
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    wet and dry filler always use production paper.
    I'm not sure what the difference is? I thought it was aluminium oxide based or do you mean the process is important i.e. not introducing water?

  5. #5
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    Quote Originally Posted by regcheeseman View Post
    I'm not sure what the difference is? I thought it was aluminium oxide based or do you mean the process is important i.e. not introducing water?
    process I think.

    the old man always used to go onto bare metal when he had his bodyshop.
    Alan says: Selling the $hit in the garage pays for new toys

  6. #6
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    some fillers are porous, if you sand them wet, the metal behind the filler can start to corrode . Rust can exert 2500lbs per sq inch so it's better to keep it as dry as possible.

  7. #7
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    Quote Originally Posted by mitty85 View Post
    I fill them prime but never wet and dry filler always use production paper.
    thats a +1 from me to!

  8. #8
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    In my huge experience I can never understand wet sanding - Filler & primer is like a sponge

  9. #9
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    it's easier/faster and less dusty?

    I also cringe when I get that dry dust on my hands, but that's probably just me being a bit of a mary. I cant deal with chalk and chalk dust either, so 2 years of teacher training was a dumb idea really!

  10. #10
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    Polyester based fillers are porous, but aluminium based fillers are not porous. Learnt that from practical classics i read today. They doing a body filler test.

  11. #11
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    this is a chicken or egg question, the answer depends on who you ask,

    for me i find sealing the metal before anything else means i can then wet and dry it, wet sanding will always gives a much smoother finish.

  12. #12
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    this is a chicken or egg question,
    Indeed hence the title.

    I've always put on the primer first, simple because when I've worked on cars that have been filled with no primer first, they are often rotten behind the filler but then that may just be down to poor prep to begin with.

    Then you have the adhesion problem of filler onto paint...

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