SR ROLLA

Phosphoric Acid Metal Prep

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I've been stripping my car back and am just about at the point where I can start putting paint back on it. I found a bit of light surface rust under the old paint, so I have ended up with some large areas of bare metal. The plan is to use phosphoric acid to prep the metal, then etch prime over that. The first few (smaller) areas which I used the acid on came up a really clean and smooth matte silver. On the larger areas I have been getting a lot of streaking, some white, some yellow.

Is it normal for it too look like that? is it a case of not enough acid? Or too much? not long enough on before rinsing off? Or too long? not washing off properly? This is the first time I've used it and I'm struggling to find good reference online for how it should look.

This is one of the panels (The previous re-painter was a big fan of aggressive wire brushing it seems):
o2usdyny.mii.jpg

Once this is sorted is it sufficient to just scotchbrite and wipe down with wax and grease remover before spraying? I had Por-15 suggested to me, but reading through some of the posts on here the general consensus seems to be that it's pretty shit and not worth bothering with, so straight to an etch primer?

Cheers for any advice, pretty new to this but have already learned a lot getting to this stage. Keen to get the car all one colour again.

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Hard to tell but looks like you let it dry on there, gotta keep it wet. I use the acid to convert surface rust but don’t bother leaving the acid finish for paint. Once you do the acid I usually sand/scotch brite the fuck out of it until it’s white and then wax and grease. Go get some 2 part epoxy primer, etch primer is shit.

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Once cleaned and sanded, spray Brunox onto the bare steel .

It's a rust converter and epoxy primer in one.  After two-three coats a day apart and another 24 hours to cure, you can sand, two pack prime etc.

http://www.pacer.co.nz/product-group/1561-brunox-epoxy-rust-killer-aero/category/301-brunox

Watch attached video on how it works.

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Take care spraying epoxy - get the right protective gear. When I started spraying I stuck with single stage paints for safety reasons.

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Yeah have to be careful. If you look into it most epoxy primer isn't too bad, its the urethane top coats that have max isocyanate and will murder you. 3M face mask with the correct filters and some eye protection and you will live, its only primer so do it outside in the driveway for extra safe points.

In straya you can buy phosphoric acid at Bunnings in the paint thinners section under the name ranex, its expensive but convenient.

Problem with single stage solvent cured paint is its million years old technology. Nothing beats a good 2 part epoxy primer for adhesion to metal, same for top coats urethane lasts for a zillion years and is low upkeep.

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My thinking on not using better, 2 part paint products while still very much a beginner was partly because of the increased toxicity, and the need for a higher level of protective gear, ventilation etc. Also, I thought it's illegal to spray those paints in suburb home garage type places? Not sure where I heard that though…

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For cleaning with phosphoric acid its easiest to do small sections at a time, as mentioned here

The stuff from Resene had the highest phosphoric acid content that I could find otherwise Bunnings etc in the paint section as mentioned.

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Is all this hardcore acid actually better than the non-toxic alternatives?

I've done test patches and the rust is gone quick, and that's with stuff that isn't acid / doesn't give of fumes etc.

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40 minutes ago, slopez said:

For cleaning with phosphoric acid its easiest to do small sections at a time, as mentioned here

The stuff from Resene had the highest phosphoric acid content that I could find otherwise Bunnings etc in the paint section as mentioned.

This stuff also has a high concentration and works wonders on rust.

https://www.mitre10.co.nz/shop/quik-rust-remover-500ml/p/239274

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I've used Kephos 253. 

It's phosphoric acid Bourne in a solution of xylene. Dries fast etc. But wear a respirator.  Otherwise it will blow your head off. (Even usng it outdoors it'll make you high as fuck)

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5 hours ago, SR ROLLA said:

My thinking on not using better, 2 part paint products while still very much a beginner was partly because of the increased toxicity, and the need for a higher level of protective gear, ventilation etc. Also, I thought it's illegal to spray those paints in suburb home garage type places? Not sure where I heard that though…

It is illegal to be painting cars at home. Fumes are meant to be vented and filtered before reaching the outside.

I had a go at a neighbor for painting a car outside his house,my 2 kids under 3yrs old were in their splash pool 20ft away. It's not a good thing to be doing. If you would wear a mask to paint,why expose others to the toxic fumes and no fucks given?

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You would have to look into the laws in your area, ie here in Brisbane the law is vauge and some spray painting at home is allowed as long as it is not commercial. You have to look it up, It was legal to spray my car in the driveway and I asked/told the neighbours about it.

I mean guys reseal roofs with spray in open atmosphere, I have seen the exterior of homes spray painted. Case by case for your council.

Bling phosphoric acid is not hard core, I buy the bunnings shit and dilute it a little further depending on the job. It doesn't sting the skin and fuck all fumes unless you boxed yourself in with a bath of it working. You can do the same thing with citric acid or vinegar for sure but the phosphoric seems to be just the right zing for panels where it takes 15-30min instead of 4 hours, when I was soaking shit in citric acid baths it takes 24-48h to work. Unsure about anything else as using acid is the gold standard as far as I have learned.

As for spraying safety I had looked it up a millon times but looked again. Modern 2 part epoxy primers are only considered mild irritants and only fuck you up over long term exposure without correct PPE which can give you allergic type reactions, they do not cure with isocyanates. They are just as shitty as exposure to single stage solvent curing paints basically so wear a mask and its all good. Its the polyurethane ( urethane primer, single stage top coats,clears etc) that cure with isocyantate and are considered extra death spec which gets absorbed through the skin and can build up toxicity.

 

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3 hours ago, Benno said:

I'd choose the Brunox instead, as once it's chemically converted it, the epoxy seals over as a base for two pack primers.

It's pretty much the only product Repair Certifiers are approving to kill/cure rust with the exception of sandblasting, and then the  bare metal is sprayed with Brunox once blasted.

Got one vehicle in compliance at the mo with a few small spots, and this is what they are using.

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1 hour ago, Spencer said:

Bling phosphoric acid is not hard core, I buy the bunnings shit and dilute it a little further depending on the job.

I'm only talking hardcore relative to other products you can buy that don't contain acid. Most of them claim to be safe on skin (I still glove up because why not). But acid is certainly not great for your skin.

This was ~2 minutes with a soft brush to put it on, cloth to wipe it off. It's left a zinc phosphate layer on the metal and all the rust is gone. Deeply pitted metal will take longer of course. Deeply pitted vertical surfaces are a nightmare. It's great for heard to reach places though as you just brush it in and presol it when done.

/many ways to skin a cat

 

4x3khaaz.r0i.jpg

 

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Phosphoric is great stuff, I've got a shell in bare steel with it on it and the panel shows little sign of oxidation after a few years....

My tips?  Dilute it 3-1, apply it by soaking a rag and wipe it on, have another rag to wipe off the excess.  Then after dry, wipe with thinners and a rag.  Stopped having all of those yellowing/oxidation problems after doing that. 

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