Rust spots in coving through polyfilla & primer - what is going on?

Discussion in 'Other Trades Talk' started by To DIY or not DIY, Feb 25, 2021.

  1. To DIY or not DIY

    To DIY or not DIY New Member

    Doing up a bedroom (new floor, skirts, coving, decorating) where nothing is straight. After a lot of research I decided to use nails to put in the coving (I know it's not ideal but it was just not staying up). Covered the nail heads with polyfilla, primed them and then applied one layer of topcoat but this seems to have brought out previously invisible rust spots (see pics).

    Currently I am thinking of digging out each nail spot, re-filling/priming and using a matt white emulsion but obviously don't want to repeat the mistake but at a loss to how to avoid it, as I thought polyfilla should have been enough. What should I be using to prevent the rust coming back??
     

    Attached Files:

  2. Astramax

    Astramax Super Member

    Sheradised nails, the nail heads are rusting as can be seen, you should of primed over each nail head with, Zinsser 123 before filling.
     
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  3. AnotherTopJob

    AnotherTopJob Screwfix Select

    It's because you're using water based products straight over the nails.
    As mentioned, you need to use a suitable (oil based) primer or paint to seal the metal.
     
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  4. To DIY or not DIY

    To DIY or not DIY New Member

    Thanks Astramax & AnotherTopJob, can you put Zinsser 123 over rust ie will it be a problem if I can't sand down all the rust on the nail heads?
     
  5. To DIY or not DIY

    To DIY or not DIY New Member

    Also this may be really obvious but the product description doesn't mention you can use a filler on top. Will polyfilla take to it?

    Really glad to get your advice on this as it's really unclear which primers are definitely oil based. Even Zinsser says it's water-based which as a new DIYer is quite misleading!
     
  6. Astramax

    Astramax Super Member

    Yes you can it will be easy enough to wipe over the rust with sandpaper to remove it.
     
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  7. To DIY or not DIY

    To DIY or not DIY New Member

    Great thanks Astramax, that's brilliant. Obviously the hard bit is yet to come (I'm not looking forward to chipping away the paint/filler to get to the nail head) but glad to know what to do next.
     
  8. Wayners

    Wayners Screwfix Select

    I'd pull out. Was interesting talking to guy working with concrete and the rust from bars inside concrete and how and why it travels so far through concrete in bridges ect.
    It's like plastering beads or car rust and just a pain. It's like a cancer so decide either to punch way in or the better option to pull out and be rid of it.
     
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  9. To DIY or not DIY

    To DIY or not DIY New Member

    Thanks Wayners - yeah it would be better to get to the root cause but I assume pulling the nails out of coving will be as painful as it sounds. Either way it's been a steep learning curve!
     
  10. CGN

    CGN Screwfix Select

    Aerosol of Zinsser bin.
     
  11. Wayners

    Wayners Screwfix Select

    If I was doing that I'd get my grinder and horizontal slot grinding off nail then as above use zinsser bin in spray can warmed a bit. Ronseal 2 pack resin filler nicely so minimal sanding as no water in that and 120 / 180 grade sand paper to smooth then paint
     

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