Removing Magnesium from SS Propeller

Posted By: Jack T

Removing Magnesium from SS Propeller - 04/14/19 08:25 PM

Because our boat is on fresh water all summer, I use magnesium sacrificial anodes. I also have a stainless steel propeller. Over the summer, the propeller gains some surface roughness that I presume is magnesium. To remove the "extra" metal, a well formed fingernail does an excellent job of removing it. However, in some locations, the build-up is heavier, and removing it this way will not work.

Because it is SS prop, standard steel tools and abrasives should not be used to make the cleaning faster. I have tried a number of #M abrasive sheets, but they do a poor job of lifting the magnesium. Yesterday, I bought some bronze wool cleaning pads. They work well, except around the hub which has a heavier deposit. In the past, I have used Dremel cleaners that are basically made from 3M type material. They have done a pretty good job, but were slow. They are also quite expensive individually and last year, I used about 10 of them.

I have also tried solvents like paint thinner and lacquer thinner, but no progress. I even tried a bottle of chrome wheel cleaner (acid) and the edge of some Plexiglas to no avail. I am thinking a brass wool pad might work, but haven't tried it yet, because they are not readily available in the local stores. And, not available in a form that can be mounted to an electric drill.

So, what recommendation can you guy make that will get this prop cleaned up in a shorter time?
Posted By: Frantically Relaxing

Re: Removing Magnesium from SS Propeller - 04/15/19 06:54 PM

go to Home Depot, buy a bottle of The Works toilet cleaner (about $2), it should say that it's 10% Hydrochloric acid... put on some rubber gloves and dab a bit on the deposits. If it starts smoking, it'll work. If not, take it to the bathroom wink

BUT, if it does work, put a small drop on the prop somewhere inconspicuous and wait a couple of minutes to see if it darkens the stainless. I used it several times on the Chap's DP props, never did squat to them other than quickly remove the calcium, but SOME SS will darken- like rub and grab rails, kitchen sinks...

It's funny stuff, it'll eat 6061 aluminum but won't touch 5052. You can cut it down to 7% or so with water and should still work fine, and pretty sure it'll eat magnesium, and pretty quickly...once it stops smoking, the acid has been neutralized, add more. After 5 or 6 doses rinse everything and the area with water. When fresh stops smoking, deposit are gone smile

Many seem to be wary of muriatic acid, but I love the stuff. FWIW, I don't know how many times I've used MA cleaning my hulls and drives on the harbor's and my own lawn, and neither theirs nor our lawn has ever shown any effects whatsover. Even working on my cement driveway it never seems to 'clean up' the cement, probably because I DO rinse often.. .
Posted By: Jack T

Re: Removing Magnesium from SS Propeller - 04/15/19 10:11 PM

Thanks for responding, FR. I just finished using stainless steel "wool." Not fast, and had to finish off some spots with the Dremel that I couldn't get into with the SS pad. Some very fine scratches showed up after I was done-and some burn marks from pressing the Dremel too hard that the 3M tool got hot and turned some spots black. You know, they showed up, and I immediately went to the dark spots and made more--dummy, you should have figured that out.

When I was all done, I used some white polishing compound and it seemed to take care of some of the "imperfections." Not professional, but I save myself $60 to have a professorial polish the prop to a mirror finish. Not real critical, though, because the magnesium will show up again after the boat sits in the water all summer.

FR, I will try to remember what you said next year and try it out.

BTW, if anyone else has a possible solution, please let me know.
Posted By: Frantically Relaxing

Re: Removing Magnesium from SS Propeller - 04/16/19 03:54 AM

this is what the stuff will do to an aluminum Michigan Wheel prop if you're dumb enough to soak it in a bucket of 10% MA-- and forget you did facepalm
--this was soaking for about 1/2 hour, and was just a'boilin' when I finally got back to it.
ya DO have to respect the stuff! bow
[Linked Image]

Posted By: Frantically Relaxing

Re: Removing Magnesium from SS Propeller - 04/16/19 04:14 AM

as for GOOD results, about 7% muriatic acid (3:1 water to 20% acid) and a pressure washer was able to change THIS:

[Linked Image]

[Linked Image]

to THIS-

[Linked Image]

The first 2 pics, the boat was only a few months old! The 'clean' pic was taken just before we sold it 4 years later. But it looked that good after every acid wash. And I NEVER used a brush- I powerwashed the vegetables off, then used a garden sprayer and a water hose to spray the acid and rinse down. A quick wipe down afterward is all the elbow grease I ever used...
Posted By: GoFirstClass

Re: Removing Magnesium from SS Propeller - 04/16/19 04:50 PM

FR, how did you apply the muriatic acid to the boat and lower unit?
Posted By: Frantically Relaxing

Re: Removing Magnesium from SS Propeller - 04/17/19 07:17 PM

The cheapest garden sprayer I can find. Do a square foot at a time, rinse well, move on...
© 2019