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Fri Dec 22, 2023 9:47 am

I've been experimenting with muriatic acid for removing rust for some time now. Initially, I'd brush the product on the surface repeatedly to keep it wet and it seemed pretty effective.

I was recently turned on to a new technique of using paper towels or toilet paper soaked in acid. The toilet paper will actually cling to a vertical surface. 24 hours or less will get off strong surface rust. I thought I'd share it here as I'm amazed with the results.

Fri Dec 22, 2023 9:52 am

The door skins were treated for less than 24 hrs. I didn't soak the bottom since it's getting replaced.

Fri Dec 22, 2023 9:59 am

Another technique I've been using is diluting the acid with water and dunking the parts. I put a couple of gallons in this covered garbage can and filled it up about halfway with water. I soaked a rusty wheel for about a week and it came out looking like new metal (except for the pitting).

These 356 parts were mostly surface rusted, so nothing heavy, but this was overnight in the diluted mixture which has been in the garbage can for a few months now:

Clearly, half of the part was submerged.

Fri Dec 22, 2023 10:08 am

If you do try this technique, use common sense and read the bottle for safety instructions. DO NOT use the acid indoors. I learned this when I was using it on a 356 for the first time. I came back the next day and every hammer, dolly and ferrous surface in my shop was surface rusted. I'd recommend not spraying it. I just use a chip brush and mottle it around. Save the mushed up remains in a plastic bag and use them again and again. Rinse with water. Spray on your favorite phosphoric acid based prep product, (Ospho, Metal Prep, etc...) and you're done. A gallon of the acid is about $10 and goes a long way.

Try it, you'll like it!

Fri Dec 22, 2023 10:30 am

Amazing

Fri Dec 22, 2023 11:39 am

You will need to neutralize the acid after you apply it onto the metal.

Fri Dec 22, 2023 4:06 pm

Does it harm original paint? Or is it only for surfaces where saving paint is not an issue?

Fri Dec 22, 2023 5:47 pm

It will lift some paint if left on long enough. The original primer on the inside of the door frames completely came off overnight, while enamel painted surfaces tend to be more durable. The wheel I left in for a week had some paint loss, but not completely. I wish!

The beauty of this process is that you can isolate where you want to remove the rust by only placing the TP where you want it.

Fri Dec 22, 2023 5:51 pm

heimlich wrote: You will need to neutralize the acid after you apply it onto the metal.

That would defeat the purpose. The acid is what's dissolving the rust. Water rinse followed by phosphoric acid to keep rust at bay.

If you're talking about prior to paint, that's understandable, but there is a lot of prep to go on this panel before paint will touch it.

Fri Dec 22, 2023 6:01 pm

the before and after pictures for rust removal are impressive!

Fri Dec 22, 2023 7:16 pm

Bulli Klinik wrote: heimlich wrote: You will need to neutralize the acid after you apply it onto the metal.

That would defeat the purpose. The acid is what's dissolving the rust. Water rinse followed by phosphoric acid to keep rust at bay.

If you're talking about prior to paint, that's understandable, but there is a lot of prep to go on this panel before paint will touch it.
And therefore netralizing the MA :wink:

Some colors may do OK, others (reds and oranges for example) might bleach or yellow. Test a small sample first.

Fri Dec 22, 2023 9:20 pm

Bulli Klinik wrote: heimlich wrote: You will need to neutralize the acid after you apply it onto the metal.

That would defeat the purpose. The acid is what's dissolving the rust. Water rinse followed by phosphoric acid to keep rust at bay.

If you're talking about prior to paint, that's understandable, but there is a lot of prep to go on this panel before paint will touch it.

I should have been more detailed in my response to you. You apply it to the metal, let it do its thing, and then you neutralize it. If you don't it will continue eating away. I've always used full strength muratic which is a little diluted already but you've diluted it even more so maybe it is not so bad.

Fri Dec 22, 2023 9:54 pm

Be very careful when using this, it is very volatile. This can be very dangerous if you haven't been trained in using acids. Never add water to acid. But you can add acid to water. Get it wrong and it will explode.

Fri Dec 22, 2023 11:06 pm

I just mix it. Your results; explosions, etc.. may vary.

Sat Dec 23, 2023 4:07 am

I used muriatic acid on the small pulley in the photo and it worked so well I used it on the vw crank pulley I thought was shot. This was around 2020. When I did this I think it was submerged overnight.

Sat Dec 23, 2023 7:22 am

wow, good to know, rust is evil

Sat Dec 23, 2023 8:49 am

I'm glad you had similar results.

Just to clarify, I'm using Kleen Strip brand MA, available at the Home Depot. Apparently this has 90% less fuming that standard MA. I didn't see any specification as to the percentage of active ingredients, so I'm unsure if there are stronger versions out there. This one has been working fine, but if someone finds a cheaper source, feel free to inform us. I'd like to buy it in a 5 gallon container to use in the garbage can.

I also use Kleen Strips version of phosphoric acid as a final wash, mainly because it's readily available at the hardware stores. I'm all ears for any other suggestions.

If any chemical engineers would like to chime in to enlighten us on some details of what's happening and better ways, please do.

Sat Dec 23, 2023 9:15 am

Bulli Klinik wrote: This one has been working fine, but if someone finds a cheaper source, feel free to inform us. I'd like to buy it in a 5 gallon container to use in the garbage can.

I remember it being 10% HCL. You might look at pool cleaning places. I've heard they use it.

Pickling steel is part of the process you are using.

Sat Dec 23, 2023 9:28 am

I did the same technique on a heavily rusted hood only with paper towels; worked well. After rinsing, I brushed on some Ospho (mostly phosporic acid) to stop flash rust. Do it outdoors like others said.

Sat Dec 23, 2023 9:55 am

I use Phosphoric Acid-only.
You can buy it at metal supply stores or sometimes online depending on your state. Muractic is too volatile.
Phosphoric acid won't hurt paint, it attacks only rust. You may need to brush it a bit between soaking or spraying.
If you need to remove hard-core stuck and rotted/hard rubber (like window frames) use simple green for about 3 days (soak) it peels off like butter-it can even soften it up if used wisely.

I've done many pop-outs this way before prepping to blasting, but doing it this way, blasting is optional, sanding is a must either method, either acid. Muractic is just too nasty.