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  1. #1
    Join Date
    May 2009
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    melb
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    Default Newby painting/preping steel

    I bought some mild steel from Surdex over the weekend. Its not painted or anything and just coated in oil.

    I cleaned the oil off and I notice that the surface is really dark. Do I need to remove it prior to priming + painting?

    I removed some of it with a flap disc and its much shinier under the dark layer.

    IMG_20210620_175514.jpg

    Also, with paints in bunnings is there much difference between this Rust-oleum, White knight and Dulux?

    White knight is much cheaper

  2. #2
    Join Date
    Dec 2013
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    56
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    Default

    It's best to remove the mill scale, or over time it removes itself taking your paint with it.
    This is why companies have things sandblasted to remove mill scale, weld splatter, etc.

    As for paint its all metal paint, but depends on the purpose.
    If it's a piece of furniture and needs to look nice I'd go with a quality paint.
    On the other hand if it's a shed bench use the cheap stuff.

    I use Supercheap export spray cans as there really cheap, and I don't bother with primer for a bench etc.

    Sent from my 5007U using Tapatalk
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  3. #3
    Join Date
    May 2009
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    melb
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    Default

    Is this the best thing to use to remove it? 3M clean and strip?

    https://www.blackwoods.com.au/abrasi...5mm/p/05342529

    I saw on youtube you can use vinegar too for smaller parts

    In regards to the steel you can buy that is painted blue - is that 'undercoat' - with that I only need to put primer on the areas where the blue paint has been stripped?

    I would like a nice finish its going inside the house

  4. #4
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    Default

    I use a Flexovit disc identical to the one you linked, I get them from Bunnings generally, cheaper than Blackwoods.
    If you’re building furniture, I’d suggest giving serious consideration to having it blasted. The results will be way more consistent.
    If you’re building with blue painted steel, strip it all with oven cleaner. It’s an industrial paint that doesn’t provide particularly good adhesion for other paints. The blue paint serves only to stop the steel rusting in storage.
    As has been mentioned, for furniture use quality paint. I tend to use Automotive enamel from a crash repair supplier and apply it with a HVLP gun if I’m painting, which is rare these days because I tend to favour powder coat now it’s evolved to an almost limitless palette.

  5. #5
    Join Date
    Apr 2019
    Location
    Adelaide
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    589

    Default

    Definitely remove the rubbish blue paint. More shiny is more better. I would buy the strip n clean disks from smith and arrow. Good product.

  6. #6
    Join Date
    Sep 2010
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    Lebrina
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    Default

    I don't know where people get the idea that the blue primer must or even should be removed prior to painting, as there is no good reason to remove sound paint. If your blue factory primed steel has been laying around outside and is rusted, then that's a different matter. Standard industry practice is to run over the steel with a random orbital sander and 80 to 120 grit discs, then to etch prime followed by 2 pack high build undercoat before the final colour is applied. The etch primer could be deleted, but it does improve adhesion and the 2 pack high build could be substituted for a conventional single pack steel primer. In industry nobody removes the blue undercoat as it would be a time consuming, $$$ burning undertaking that provides no positive benefit. As for sand blasting, nobody does that without a really good reason as it is damn expensive and adds its own challenges when it comes time to paint. The same goes for the tube that the OP is using. Sand it with 80 to 120 grit, wipe it with wax and grease remover prime it and top coat.
    I have had good results from the Metalshield range of paints, although I do prefer proper spraying enamel or 2 pack.
    No point making life harder than it needs to be.

  7. #7
    Join Date
    Nov 2007
    Location
    melbourne australia
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    3,228

    Default

    Quote Originally Posted by Karl Robbers View Post
    Standard industry practice is to run over the steel with a random orbital sander and 80 to 120 grit discs, then to etch prime followed by 2 pack high build undercoat before the final colour is applied.
    What's the point in etch priming a painted surface?

    From the Dulux website: https://www.duluxprotectivecoatings....ch_primers.pdf

    "Etch primers work by acid etching the metal surface. Therefore they have little effect on previously painted surfaces (including precoated sheet steel such as Colorbond
    ®). In fact, the phosphoric acid present in the etch primer may interfere with the adhesion of subsequent coatings, causing delamination."
    Chris

  8. #8
    Join Date
    Nov 2004
    Location
    Bungama SA
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    52
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    960

    Default

    Quote Originally Posted by Karl Robbers View Post
    I don't know where people get the idea that the blue primer must or even should be removed prior to painting, as there is no good reason to remove sound paint. If your blue factory primed steel has been laying around outside and is rusted, then that's a different matter. Standard industry practice is to run over the steel with a random orbital sander and 80 to 120 grit discs, then to etch prime followed by 2 pack high build undercoat before the final colour is applied. The etch primer could be deleted, but it does improve adhesion and the 2 pack high build could be substituted for a conventional single pack steel primer. In industry nobody removes the blue undercoat as it would be a time consuming, $$$ burning undertaking that provides no positive benefit. As for sand blasting, nobody does that without a really good reason as it is damn expensive and adds its own challenges when it comes time to paint. The same goes for the tube that the OP is using. Sand it with 80 to 120 grit, wipe it with wax and grease remover prime it and top coat.
    I have had good results from the Metalshield range of paints, although I do prefer proper spraying enamel or 2 pack.
    No point making life harder than it needs to be.

    Yes remove the cheap primer if your doing good quality paint over top especially for outdoor use, I would not trust a cheap as they can find primer under nice paint... made that mistake before ended up doubling the cost
    ....................................................................

  9. #9
    Join Date
    Dec 2013
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    56
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    Quote Originally Posted by jack620 View Post
    What's the point in etch priming a painted surface?

    From the Dulux website: https://www.duluxprotectivecoatings....ch_primers.pdf

    "Etch primers work by acid etching the metal surface. Therefore they have little effect on previously painted surfaces (including precoated sheet steel such as Colorbond
    Newby painting/preping  steel). In fact, the phosphoric acid present in the etch primer may interfere with the adhesion of subsequent coatings, causing delamination."
    I was thinking the same.
    Also with sandblasting it's the best sticking surface I've ever painted in my life with no problems ever.

    He has never blasted anything of mine because of distance, but my brother in-law is a blaster painter for 25 years, may I need to let him know he is not needed these days for general blasting and painting.

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  10. #10
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    Default

    Quote Originally Posted by Karl Robbers View Post
    I don't know where people get the idea that the blue primer must or even should be removed prior to painting, as there is no good reason to remove sound paint......

    ....No point making life harder than it needs to be.
    Depends on your application, if you’re making Ag implements that get buried in the dirt then probably doesn’t matter, if you’re charging people a couple of grand for a piece of furniture then the surface finish becomes somewhat more important.

    A couple of warranty jobs because I used the blue paint as ‘primer’ was enough to convince me to sand blast everything prior to painting, angry customers make life harder than it needs to be.

  11. #11
    Join Date
    Apr 2019
    Location
    Adelaide
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    Default

    Cheap paint = cheap finish!!

  12. #12
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    Nov 2007
    Location
    melbourne australia
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    3,228

    Default

    This stuff is good for machinery/workshop applications: http://www.ppgcpc.com.au/images/uplo...20-01-2017.pdf
    Chris

  13. #13
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    etch primer on bare metal is to act as the bonding media between the metal and the colour paint coat. It also helps with rust. Sometimes you get the bubbles under the paint if there is no etch primer or the worse, the whole patch of paint would come off.

  14. #14
    Join Date
    Nov 2007
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    melbourne australia
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    Quote Originally Posted by jackaroo View Post
    etch primer on bare metal is to act as the bonding media between the metal and the colour paint coat.
    I think most of us understand that. The previous posts are in response to someone suggesting etch primer should be applied over the blue paint that some steel tube comes coated with.
    Chris

  15. #15
    Join Date
    Aug 2011
    Location
    SA
    Posts
    10

    Default

    qwertyu, if you want the paint to last then you should remove the mill scale. It can be hard to remove. Soak in vinegar overnight the wash it off (pressure clean is best). Scotch-Brite's clean and strip are excellent but I haven't used them direct on heavy mill scale.
    As for White knight you get what you pay for (I've used it but won't again)

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