View original topic: Rust Look
Rhino1966 Mon May 03, 2021 10:00 am

I heard there is something that you put on bare metal to give it a rust look. The longer you leave it on the bigger effect then you rinse it off to stop the reaction. Does anyone know what this stuff is?

viiking Tue May 04, 2021 4:20 pm

I assume the metal is old metal without a zinc coating like we have on new car metal. To get rusting on the zinc coated metal you just have to use more acid to remove it first.

Any acid should give you rust staining. The acid cleans the surface leaving a reactive surface that flash rusts with water or humidity. With safety protections of respirator, goggles and rubber gloves, you could use diluted pool acid (Muriatic - HCl) or use the safer Citric Acid (food acid - available usually from home beer making suppliers) or plain old vinegar. Obviously if you are concerned with your safety in doing this, use the safer methods but remember any chemical is a potential problem. Even water is fatal if you drink enough of it. True!

You could use Ospho (phosphoric) but it tends to leave a phosphate coating that slows (but doesn't completely stop, the rusting process) in other words it takes a while to get rusting to reoccur).

Once you get to the level of rusting you want you need to stop further rusting you need to neutralise any residual acid using bicarbonate of soda or an alkali of your choice.

However, rusting will continue with exposure to air and humidity. Once you get the level of rusting you want, you will have to seal the metal to prevent air getting to the metal which causes the rusting with a coating that people use when they have patina. Some clear coat, some use lanolin or WD40 or some of the other proprietary sealers. If you want to create lines or streaks, just cover the area you don't want to rust with a light oil on the surface to keep the acid off the surface.

Before you go and do large sections of the car, I would suggest you do a small section and see if you get the result you want. In humid air, rust staining should start in a few days.

There's plenty of info on the web if you type in rusting steel with Muriatic acid. Some formulas add hydrogen peroxide but that is not necessary in my opinion.

Rhino1966 Tue May 18, 2021 5:14 am

Thanks for the reply. I am stripping all the paint off using a sander and grinder so there should be nothing but bare metal. Using the pool acid what ratio do you think I should dilute it to? Also never dealing with it does it come in powder or liquid? And do I just rinse it off?

Rhino1966 Tue May 18, 2021 5:17 am

Just re-reading the post. The acid just removes any residue so the metal rust easily naturally? It doesn't actually cause the rust?

viiking Tue May 18, 2021 4:24 pm

OK. If you don't know whether the pool acid comes liquid or powder then I think you need to go down a safer route.

Just go to the supermarket and buy some vinegar. I think you can buy it in those gallon jugs. (I'm not in the US so not familiar with brands). Once you sand off the paint to the bare metal, just paint on the vinegar. Leave it for a few days. The more humid it is the quicker the reaction should be. So if you have some rainy weather, the rust will start quicker.

The acid itself removes any "oxide" layer and makes the steel very reactive to start rusting again. That is, it starts rusting naturally. Look up "flash rust" and you can see it is the bane of all car builders after rust converting steel. In your case you only want a thin, relatively uniform layer of rust to start on the surface.

For example the reason that aluminium does not "rust" is that when you remove the outer coating of aluminium it re-forms the oxide layer and in the case of aluminium this is very stable and does not continue to "rust".

finster Wed Jun 09, 2021 11:24 am

there is also rust paint which will protect the real metal of your car but when sprayed with activator will give a rusty effect...

Rhino1966 Thu Jun 10, 2021 2:29 am

Thanks for the info. I am looking for something different without spending $4000 on a paint job.

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