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Thread: Newby painting/preping steel
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20th Jun 2021, 07:27 PM #1Intermediate Member
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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
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20th Jun 2021, 08:16 PM #2
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.
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20th Jun 2021, 10:18 PM #3Intermediate Member
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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
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20th Jun 2021, 10:59 PM #4Most Valued Member
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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.
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21st Jun 2021, 02:37 PM #5Golden Member
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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.
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21st Jun 2021, 07:58 PM #6Most Valued Member
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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.
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21st Jun 2021, 08:31 PM #7Most Valued Member
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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
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21st Jun 2021, 09:50 PM #8....................................................................
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21st Jun 2021, 09:54 PM #9
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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21st Jun 2021, 10:56 PM #10Most Valued Member
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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.
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22nd Jun 2021, 12:07 AM #11Golden Member
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Cheap paint = cheap finish!!
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22nd Jun 2021, 07:40 AM #12Most Valued Member
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This stuff is good for machinery/workshop applications: http://www.ppgcpc.com.au/images/uplo...20-01-2017.pdf
Chris
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22nd Jun 2021, 03:05 PM #13Golden Member
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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.
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22nd Jun 2021, 05:08 PM #14Most Valued Member
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24th Jun 2021, 12:37 AM #15Novice
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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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