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Muriatic acid mistake!

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mariner3302

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#1
First off, if you are thinking of using muriatic acid on cast iron, STOP. Yep, STOP and don't do it. I read online and saw a video that demonstrated it as effective and a safe method of cleaning and derusting. And to that end it does work. EXCEPT (and after it was on already), I found gobs of sites and threads saying don't use it on cast iron. One said that he left it in a soak tank for a day or so and it actually softened the cast iron so much he could remove some with a fingernail. I used it to take some flash rust off the legs on my 1937 South Bend 11" lathe. Only after applying it with a spray bottle did I read that it gets in the grain and continues eating cast iron for years if not completely neutralized and/or removed. So I scrubbed the legs with Soda Ash because it was handy and a green scratchpad. The legs are all white now from the soda ash (about 50/50) rinse and scrub. The worst is I am now worried about painting the legs.
So the question is, will soda blasting neutralize muriatic acid on cast iron or would media blasting with black diamond be enough? The legs are almost all back to metal except a couple spots where the black original fillers were applied.
 

markba633csi

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#2
After neutralizing you should be OK, HCL is nasty stuff, don't store it near your good tooling the vapor rusts everything
Mark
 

mariner3302

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#3
Yeah, read about a guy who had some in his shop and rusted everything exposed to air! I threw that stuff out and it makes me think it could have been responsible for some things rusting lightly in the shop.
 

markba633csi

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#4
It used to be sold in very thin poly bottles and strong (36.5%) and I had some in my garage. One of the bottles had a tiny crack in the plastic and over time I started seeing rust on my tools- Fortunately I caught it in time- I store it outside now- one of my mikes seized totally and got ruined
M
Ironically it's very good at removing rust when in liquid form
 

Cadillac

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#6
One thing to also remember that I found out the wrong way is. Is Cleaning outside calipers or layout pointers with a spring steel hoop on top. DONT CLEAN SPRING STEEL WITH VINEGAR! I recently got some dividers from a garage sale really nice made in Germany. Had minor rust figured a little soak in vinegar which I’ve done a lot with great results. Just never spring steel. Well ten mins. Soaking I went to brush and found the divider in pieces. Hoop was broke in pieces and arms were just laying there. S.O.B! At least it was only two dollars but a lesson well learned! I would never use muratic acid for steel just for the fact that it rust just as bad afterward as before cleaning and it stinks. Only use that for etching concrete.
 

Tozguy

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#7
To the original question on neutralizing acid soaked cast iron I would imagine a generous spray of some caustic oven cleaner on the part will neutralize the acid in the pores of the CI. Sodium hydroxide (lye) has long been used to clean steel and cast iron (BUT NOT ALUMINUM) car parts. Do a test on a small area first as there may be a strong reaction at first. Once all the acid is neutralized I would wash with water and dry quickly. Use a good rust preventing primer before painting.
 
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machinejack

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#10
Had a 1 gal plastic jug of sulfuric acid under the bench. Over time it ate thru the jug and now I have a 1 foot crater under the bench clean thru the 4" concrete. Nasty stuff these acids.
 

Tozguy

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#11
Also beware of silicone caulking tubes, the ones that smell vinegar (acetic acid).
If stored close to steel they will promote rust over time. I store my silicone tubes in heavy plastic bags.
 

cathead

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#12
HCL = hydrochloric acid, the name of the acid component in muriatic acid.
HCl is hydrochloric acid. The first letter in an element is capitalized and the second letter of that same element is in lower case, thus: Cl.
 

BtoVin83

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#13
The rusting will not stop by neutralizing, it's the chlorine that is the culprit. There are products to pull the chlorine out of the steel. We had a customer store bleach in a bare steel tank one time, after multiple cleanings and neutralization it would start rusting again. Eventually it had huge holes rusted through the tank.
 

mariner3302

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#15
I'll never let that crap near my shop again, that is a fact! I guess I need to powerwash it off the garage floor now. What a mess it will make. All because I thought I could save 10 minutes, argh...
 

pontiac428

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#16
Don't curse the tool for the manner in which it is used. Strong acids and bases in high concentrations do attack metals. The idea is to select and control the strength and contact time for the desired effect. Before trying to use a blast furnace to cook a hamburger patty, consider if it is the right tool for the job. If you want to give a rusted part a quick (and carefully observed) dunk in a tank of diluted HCl, it will do the job nicely. Just like your hamburger patty, you remove it from the grill just before it cooks to the pink color you like, because the meat continues to cook after it comes away from the heat. The acid will continue with a secondary reaction on an iron part when exposed to oxygen in the air that further affects your part. Neutralizing with baking soda followed by a rinse does just fine. At this point, oil, paint, or preserve your part. It will look nice!

I want to kill the rumors about never using lye (NaOH) on alloy. I use it all the time on cylinder heads after tear-down. Lye reacts with oil and water to make soap (saponification reaction), removing otherwise difficult to clean oil and coke from the heat-cycled metal. I use oven cleaner for convenience, assisted by brushes, green scotch-brite, and good gloves (any type of impermeable rubber is okay for acids and bases). Contact time is kept short and the part is rinsed often to ensure I'm not over-doing it. The resulting finish on aluminum is the same hard oxide that forms on exposure to air. I use this prep method on all kinds of aluminum parts to remove oxidation deposits, scale, grease, and coked oil. No neutralization necessary, just rinse.

These processes require supervision. You can't just drop parts in a full-concentration tank and walk away while the bubbles do the work for you, or you'll find out the hard way just how strong these commodity chemicals really are!

Another safety note, don't store your strong acids in the same place as oil-based chems... If they come into contact, the acids will quickly oxidize the hydrocarbons in the oil, which is a fancy way of saying it could cause a hot chemical fire.
 

mariner3302

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#17
Very true, Pontiac! Thanks I initially thought that what I was doing was correct and safe but I was wrong. I see now that I was nowhere near prepared or informed on it's proper use which was totally my fault. I'm glad I only put it on the legs and took it off after about 10 minutes. After scrubbing the legs down with the soda ashh solution, I media blasted them, washed with soap and water and rinse. Now there is a bit of flash rust that I intend to cover with a rust converting paint. Probably Rustoleum Rust Reformer or, if not available, I'll go to Sherwin Williams who mixed the paint I will be using on the lathe.
 

Tozguy

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#18
Another lesson I am taking from your experience mariner is to beware of what can show up on utube. It is not always good stuff to imitate.

As to cleaning aluminum alloys with NaOH, check the chemistry involved and decide if it suits your purpose. It is not a rumor that lye reacts with aluminum. Lye could possibly react more readily with the aluminum than with the fouling that you want to remove. Beware of anyone who tells you different. I for one have been there done that and now avoid it like the plaque.

Using acids or alkalies is a last resort for me because of the disposal problem when done and because of the other viable options that are available.
 

mariner3302

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#19
From a close friend of mine who is a chemist:

Of all the acids with which I’ve worked I dislike HCl most. The fumes not only take your breath away, but they hang around for what seems to be an indefinite period. The fumes deposit on “everything” and continue fuming albeit not in a copious cloud. This is the source of the rust and it will continue to rust if painted over, which you already know.

We used a scrubber to clean metal, which was nothing more than rollers with metal bristles un a water wash. We used caustic baths that contained wetting agents and corrosion inhibitors to remove surface oils and dirt. Phosphoric acid isn’t as aggressive on metal as HCl or nitric acids, but the benefit is that it polishes the surface of the metal. It requires longer treatment (soaking) but it leaves a smooth finish.
I’m guessing the HCl was 25 – 35%. I’m not sure how it was applied (concentrated or diluted), nor do I know how it was neutralized or for how long. Your description indicates you scrubbed it with a scotch pad. The metal “softens” due to the microscopic rust pockets in the pores. I’m not familiar with the terms “soda blasting” or “media blasting”. A better choice for removing rust would have been a salt vinegar bath or a commercially available rust remover such as Metal Rescue, but the damage has been done, so how to clean it up.

How long did you soak the leg in the acid and for how long did you neutralize it? Did you neutralize immediately after removing it from the acid (after rinsing) or did it dry out first with neutralization following later? Neutralization should be 1 – 2 times longer than the acid dip. Rinsing should take a while to ensure the removal of residual acid (unreacted) and neutralization salts. A second base dip and rinse couldn’t hurt. The part should have been thoroughly dried and then put before a fan. We would use drying followed by placement in a forced air dryer and subsequent placement in a desiccator. Without the desiccation, the part should receive a base protective coat to prevent rust. If you aren’t going to paint it, use an oil to coat the part for rust prevention. This could be removed with a caustic bath.

So, try a wire cup brush on the legs. Check with the guys at Lowes or on the website for which gauge wire is best. If your neutralization period was shorter than your acid dip, repeat neutralization, then dry and coat.

A photo of the leg would help as there are other scrubbing techniques.

Long answer, but I hope it helps. Sometimes it is easier to buy ready-made products for “consumer” metalworking because they have the wetting agents and corrosion inhibitors in the formulations.

I replied:
I used heavy duty Easy-Off and aircraft paint stripper to get the grime and paint off. Then I sprayed them with the Muriatic Acid undiluted from a spray bottle. 31.0-35.0% Source: http://www.jasco-help.com/uploads/general/Jasco_Muriatic_Acid_GJMA220_MSDS.pdf It was on for about 10 minutes when I read that it could soften and basically melt the cast iron. I rinsed the acid off for a minute of two. Then I mixed about 2 cups of soda ash to 2 cups of water then scrubbed the legs with a green scotchbrite with copious solution. I kept stirring the solution to keep it from separating. I let the solution sit overnight. The next day there was a white powder on the concrete floor of the shop. I rinsed that off and then blasted the legs with a coal slag type of sand.

After that I scrubbed them down with a soapy water solution then rinsed them off. That was Saturday. They have been hanging since. I was going to primer them with a rust remover/converter then top coat with 2 coats of a Sherwin-Williams enamel.

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MrWhoopee

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#21
When I was in high school, one of my classmates poured liquid drain cleaner (concentrated lye solution) thru an aluminum funnel. He lost his eye.

Drano (non-liquid) contains aluminum "swarf", which reacts vigorously with the lye once you pour warm water down the drain. The bubbling action is caused by the release of hydrogen in the reaction. Don't light a match.
 

NortonDommi

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#22
A 100% effective and safe way to derust Cast Iron is degrease with a detergent and pressure wash then soak in a 1:40 mix of Molasses/water.
Pressure wash after soak and repeat if necessary. After rinse treat with a Tannin base rust converter and inside you will have about a year to paint or you can oil with a fish oil which can be painted at any time.
Soaking can take a while but no damage to sound iron will occur. Bigger items can have soaked rags wrapped on them and then wrapped in plastic 'cling film'. With tape I've used this on old vehicles using duct tape.
 
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