Propellor cleaning with acid?

[charles_reed]

My bronze prop is covered in a limescale type stuff, very hard to shift. Is there a chemical that might do it without damaging the metal? I have searched the forum but no luck.

Yes you can buy a sulfamic acid paste specifically for de-scaling metal components - I use Fernox DS3. It's quite possibly a zinc compound from your sacrificial anode - in which case not as effective as with limescale.

One could, of course use hydrochloric, nitric or sulphuric acid, but unless you know what you're doing and take reasonable precautions you can damage yourself as well as your propeller.
Muriatic acid - soon we'll be talking about spirit of salts and philosophers' stone. I knew J K Rowling was responsible for putting the clock back!!!

 

[nigelmercier]

I think that you are referring to Muriatic acid.

About 100 years ago perhaps, and still in the USA of course.

 

[AntarcticPilot]

I recently (last week!) used Hydrochloric Acid to clean the blades of my Gori folding propeller. Soaked them in about a 5% solution overnight, then wiped them down in the morning and rinsed them off. It removed the barnacle and tube-worm deposits perfectly, with absolutely no sign of any change to the metal, not that I'd expect HCl at that sort of concentration to affect the metal of a propeller. VyvCox may correct me, but my understanding is that brasses are mutual solid solutions of the various components, and so chemical action (as opposed to electro-chemical action) is unlikely to remove one component preferentially.

I didn't remove the hub from the shaft, so could not soak that. I used a sanding drum on a Dremel lookalike tool, and found that the carbonate deposits were more resistant than the dark patina on the metal! Certainly the acid did a much better job, and had less effect on the metal. In future, I'd certainly prefer the acid based approach to using abrasives.

Perhaps worth noting that the shells of marine organisms aren't simply made of calcium carbonate - they are a sort of biological composite of calcium carbonate and material like the byssus that holds shells to their attachment. Like GRP, this material is much stronger and more resistant to damage than either material on its own. Acid removes the carbonate component, making it very easy to wipe off the remainder; abrasives have to deal with an intrinsically resistant material that is designed to hold together in a high energy, highly abrasive environment. Think of a barnacle on rocks exposed to wave action!

As others have noted, brick-cleaner is a source of HCl, and outside the UK, it may also be sold as a cleaning agent under a variety of names. Others will advise better on sourcing the stuff, though - Mrs AntarcticPilot is a research chemist, and simply got me some from the lab!

As NigelMercier notes, Muriatic Acid is a very old-fashioned name for what is now known as Hydrochloric Acid. I gather "Muriatic Acid" continues in use on the Continent, but it won't be the name found on any list of contents or MSDS sheets.

 

[Hydrozoan]

Perhaps worth noting that the shells of marine organisms aren't simply made of calcium carbonate - they are a sort of biological composite of calcium carbonate and material like the byssus that holds shells to their attachment. Like GRP, this material is much stronger and more resistant to damage than either material on its own.

I get a general carbonate 'film' and the odd tube worm, and just lightly abrade and polish. Regarding the byssus threads, there's a fascinating bit about the mechanical properties of those of the common mussel here http://mollus.oxfordjournals.org/content/45/2/219.short. 50 are enough to hold the mussel in all but severe storms, and they're laid down with a prestrain of 10% to guy it in place. Oops - sorry, starting an anchor thread (which I believe is always bad news ).

 

[KellysEye]

>I think that you are referring to Muriatic acid.

That's what I used but don't get it on your hands or body anywhere although diluted it still burns if you don't wash it off quickly.

 

[Halo]

There seems to be a concensus on brick cleaner - I agree its the answer.
On the practicalities of use I simply dilute 50/50 with tap water and immerse the parts to be cleaned. The "fizz" of dissolving calcium is immediate and I watch for a few minutes until the fizing stops then remove and rinse very thoroughly. So far a few minutes has been enough to dissolve away the calcium/barnies etc. This is one time to wear eye protection and rubber gloves and get the parts out as soon as they are clean.
Please take time to neutralise the acid with chalk or similar before disposal
Martin

 

[DickB]

FWIW I have polished my Maxiprop to a mirror finish just once the first year. Each year the limescale comes off with a green scourer and a paint scraper really easily and the polished surface is easily restored with DURAGLIT. I then coat with gooey Lanoline. I'me not sure if that does any good at all but the effort is minimal each year. This is the sixth year I have done this. BTW the deposits are pretty trivial too...

cheers

 

[Twister_Ken]

I have always used some 20 year old Disclean
This is a strong HCL brick cleaner - i do not think you can get it now due to HSE requirements but i have ot from building days
does no damage at all so the modern brick cleaner from travis perkins etc certainly will not harm anything
Just wash it off with fresh water afterwards & forget polishing
Just leave it clean

NO! Paint it. I've left it clean in the past and been faced by with barnacle fest at the next lift out. Clean it, then paint it.

 

[Daydream believer]

NO! Paint it. I've left it clean in the past and been faced by with barnacle fest at the next lift out. Clean it, then paint it.

When fitting my Brunton auto prop i was advised byBruntons NOT to use antifoul paint
The reason is that in an environment where the electrolitic action is high & the paint gets chipped away then the electrolitic action will concentrate at that point & cause imbalance etc
Seems a fair comment to me

 

[Twister_Ken]

When fitting my Brunton auto prop i was advised byBruntons NOT to use antifoul paint
The reason is that in an environment where the electrolitic action is high & the paint gets chipped away then the electrolitic action will concentrate at that point & cause imbalance etc
Seems a fair comment to me

Seems a fair comment to me too, except that with three coats of primer and three coats of a/f, there has been no sign of 'chipping' on my Flexofold.

 

[Marine Reflections]

This is a fascinating subject, with chemistry, science and performance narrowed down to a measurable outcome, but props are different and are in different environments.

I would love to have test facilities and watch how a props surface reacts to different coatings.

Either the raw metal surface of the prop faces the harsh demands on its own, or a pawn is used to take the brunt.

When brand new, the prop would probably have been polished, certainly for performance. You only have to look at the race props to see that's where we currently are in that dept.

That highly polished surface will still be under attack from all kinds eroding the surfaces, pitting them, marring them.

If the surface is rough, covered in scale or just scratched up, when you stop it's an easy place for growth to settle and grow/latch on to.


The way I see it is comparable to a bus for the growth, (ok weird example I know).

Your prop is the bus, you want to drive it around but don't want any passengers, but you have to stop at some point.

When you do, there are passengers at the doors and the doors are jammed open.
You can't stop them getting on the bus and ruining your ride.

What can you do?

Take all the seats out the bus for one. Make sure there is nowhere to sit down.

Then make the entrance and all the floor as slippery as ice, with no handrails! Nothing to grab onto or nooks and crannies to hide in.

Cut an exit out the back of the bus so when you put your foot down they all slide out the back.

Effectively you are doing the same thing when painting your prop correctly, or when polishing it, correctly.

I am sure that what we currently have is not the most suitable.
Fast forward 100 years and we would probably laugh at using a metal surface on a prop and not something that replicated sharks skin for example.

I like seeing a prop shiny and polished, bronze is beautiful.