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topic 7072

Info Requested on Muriatic Acid


Q. I have a large number of antique lock sets that have been subjected to many coats of paint of various types. Some have considerable rusting, I am trying to restore these to salable or usable condition.

I was informed by a firm that soaking in Muriatic Acid [linked by editor to product info at Amazon] would do the job as opposed to sulphuric acid.

Can you help? True or false and what proportions of water and acid?

William B. Ball
Antique Lock & Key - Calgary, Alberta, Canada


A. Muriatic acid is diluted hydrochloric acid and will do the job fine. Read the warnings and directions on the container of acid and be careful using it. I'm not going to guess what concentration is best. You can find a material safety data sheet (MSDS) on this chemical at which gives this info for free.

The acid attacks the finish and the base metal. However, once the base metal is exposed, the acid will promote rusting. Rinse off your part once the acid has done it's job, then apply whatever type of finish immediately afterwards. Hydrochloric acid is actually used in metal finishing as a cleaning/etching agent right before the finish is applied. You may want to try this out on something similar but less valuable first.

You might also want to try a product called "CLR [linked by editor to product info at Amazon]" which is designed to dissolve calcium, lime, and rust deposits. This might be cheaper and/or provide better results.

tim neveau
Tim Neveau
Rochester Hills, Michigan


A. Sir,

Muriatic Acid, approximately 31% hydrochloric acid by weight, is too strong to use directly on an assembly. If used directly on a single part, a brush may be used to wipe away the dissolved rust so that the acid may attack the layers below. The acid will remove rust many time faster than clean metal however, in an assembly, you might do serious damage to small parts with strait muriatic acid. If you must, "soak" an assembly. Dilute muriatic acid 20 to 1 and soak for 24 hours. After soaking, rinse thoroughly with hot water and brush if possible. Never never never use sulfuric acid. The last process should be lots of soap and hot water with a brush if possible. Dry with forced hot air, I use my wife's hair dryer, and apply a surface protectant.

Note; Muriatic Acid causes very painful burns that are not noticeable until the damage is done. Wear protective Protective Gloves [linked by editor to product info at Amazon] and eye protection (goggles [linked by editor to product info at Amazon]). Also, use in a well ventilated area as the fumes are harmful.

Norman B. Czerski
- Eagle River, Alaska


Q. Most I know about making sulfuric acid is you can get it out of lithium batteries - but that is not exactly something you really want to do and is expensive. Regarding the stuff I read about hydrochloric acid..yes its muriatic acid and there is no need to make it, it is a pain though to try to buy it these days, its not as commonly sold as it used to be in the hardware stores and getting it online is also not easy. However, I found a website and ordered HCl 37%, reagents.. anyone expand on that for me? is that stronger or weaker than the grade of muriatic acid from hardware store..

student - NY, New York

Ed. note: You can get Muriatic Acid [linked by editor to product info at Amazon] by clicking on the link, but it's still available in stores as well. It's about 28 percent HCl. Consumers can get reagent grade Sulfuric Acid on-line in 2-ounce bottles (it doesn't say what strength), or in larger bottles (probably of low purity) as ACID drain cleaner [linked by editor to product info at Amazon -- never mix with lye/caustic type!].

As previously noted, consumers would be much better off working with commercial household products than using these dangerous acids, which were designed for professional use by trained personnel, for purposes they weren't intended.

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