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How to un-galvanize a galvanized wash tub?

 
steward
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Hello permies, I'm trying to find/make a kettle to parch wild rice over a wood fire.  What that requires is a relatively large pot/kettle/tub that I can put on a fire, mix rice in it with a paddle and then remove from the fire to dump out the parched rice.  

I learned from a nearby elder how to parch rice last year.  He used an old wash tub that had been galvanized at one time in the past.  It was down to bare metal from the years of use.  

Does anyone know of a way to get rid of the galvanization without having to eat it slowly over the years as I wear it off into the rice?

Or alternately, anyone have an idea of another way to get either a bare metal or stainless steel kettle or pot that is big enough with a decently large opening?  The lid to a very large Webber grill would be the ideal size/shape.

I did see a guy on youtube who took a 55 gallon drum and suspended it over the fire and rotated it to parch rice. That would work but once again I'd need to get it down to bare metal somehow safely.

Thanks!!
 
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One approach that may work to strip the galvanizing layer off is media blasting. Aside from renting the equipment, you may find a local auto paint shop that will do it for you for a small fee.
 
Mike Jay
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Good idea, I'll call around and see what they'd charge.  I wonder if I need to also have the exterior blasted...
 
Mike Jay
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Just called my auto body guy and he was leery of media blasting it.  He said that once you start blasting it's hard to tell if you have all of the galvanizing off.  So you'd get a lot of it off and rough up the surface but then you may not ever know if you really got all of it off.
 
James Freyr
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I can see his concern. It may depend on if the galvanizing was an electro plating process, which is a fraction of a millimeter thick or if it was hot dipped, which can be many many millimeters thick. If it's a standard galvanized tub that I'm thinking of, I bet it's very thin and was applied using the plating process. Perhaps an aggressive blasting will do the trick.
 
James Freyr
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Maybe media blasting to remove 99.9% followed by an acid bath. Maybe?
 
Mike Jay
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That's definitely an option.  Am I right in assuming that the shiny new wash tubs at the hardware store are probably electroplated and the fuzzier looking darker grey galvanizing on a 30 year old wash tub is probably hot dipped?

I'm also calling breweries to see if any have a damaged stainless beer keg they'd sell me cheap.

Amazon has 30 quart mixing bowls but they're still a bit too small.  I wish I knew someone who worked at a school cafeteria.  I bet they'd have a way to get big mixing bowls...

My dump doesn't allow scavenging, otherwise that would be a great option.  I'll check out our Habitat for Humanity Restore this afternoon.
 
James Freyr
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Oh man a stainless steel sanke keg cut in half would be perfect. Nobody in the beer industry really uses the hoff-stevens kegs anymore, they're the ones with the hole in the side for a bung. Maybe pick up one of those for cheap, but they may also be harder to find since they were phased out with the introduction of the sanke and most have been scrapped over the years. There's millions of sanke kegs out there.

I was just thinking what do you do with the bare steel after the galvanizing is removed. That's gonna start oxidizing pretty quick. You might be right about the old tubs being dipped instead of plated.
 
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Don't know if you have access to a commercial restaurant supply house, but might want to see if you can find a mixing bowl from one of those huge Hobart floor mixers that are used in industrial kitchens.  Probably be pricey, but you would have no doubts about it being food safe.  Another option is to see if you can source a huge Wok.  I've seen them that are large enough that they would sit in/on top of a 55 gallon barrel.  
 
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Or alternately, anyone have an idea of another way to get either a bare metal or stainless steel kettle or pot that is big enough with a decently large opening?


Probably expensive, but a cast iron pot/kettle is used for many things over an outdoor fire including parched corn, so maybe would work for parched rice.
We've used a very large one for pear butter and a wooden paddle to stir.  They are used for anything from a crowd sized pot of beans to lye soap.

Here's a photo, can't tell how large in the pic, but I know they come in as big as five gallons and more?



 
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I second the cast iron.
Or maybe you could get an old copper hot water cylinder and cut one end off.
 
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How about a stainless steel steam table pan?
I get mine used at the scrap yard, but they are not ridiculous new.
 
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Zinc is used for galvanizing because it is more chemically reactive than steel and will oxidize before the steel will.  We can use this to our advantage.  You can electro deplate the zinc just like it was electroplated on to the surface.

You will need a DC power source such as a battery charger, a conductive solution, and an electrode to catch the zinc.  I assume it is the inside surface you want cleaned.  What I would do is fill the wash tube with water, add some zinc sulfate if you can get it.  Where I live, I can find it at the local garden shop as an (organic?) soil amendment.  A little battery acid will speed up the process but you may not feel comfortable adding that to a tub you will be using  prepare food.  Next you will use the battery charger to make a circuit that goes from the positive terminal of the charger to the wash tub, through the solution in the tub, to a peice of steel attached to the negative terminal of the charger.  When the charger is turned on the galvanizing will be stripped off the tub (the anode) and deposited on the piece of steel (the cathode).  This will strip the zinc first.  But, at some point all the zinc will be gone the steel will begin to corrode.  So you will want to keep a close watch on the process.

Of course you will want to wash everything when you are done.  Wood ash and lots of it will neutralize the acid you added and help protect the steel.  But, without the galvanizing it's just a matter of time before the tub begins to rust.  Steve was absolutely right about that.  If this doesn't work the most likely cause is minerals (lime) in the water you are using in which case a little acid should tip the balance...

Or you could just get a cast iron pot.
 
Mike Jay
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Thanks for the ideas folks!  I stopped by the local restaurant surplus place today and they didn't have anything that was quite right.  They did have the big industrial mixing bowls for hobart mixers but they were too pricey.  Some were aluminum and supposedly they had some stainless steel ones.

I would be all over a cast iron pot if I could find one for a good price.  I'll keep my eyes open.  Most of the time around here they have dirt and flowers in them along with a rusted out hole...

I thought about the steam table pans but they're a bit too small.  It would also be nice if the bottom was round so I could swirl the rice around well and avoid burning it in the corners.

One thing that looked tolerable at the restaurant supply place was a clam shell cover for a steam pan.  If I open it up to form a half circle and sheet metal screw the overlap in place, it would act as a pretty deep bucket.  But it would have corners that may be hard to mix rice in.  They had them for $35 so that is on the list of options.

No call back from the local brewery yet...
 
Mike Jay
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Thanks Alex, I was typing when your reply came through.  Would that method work for hot dipped galvanizing as well?

How long does it take?  Minutes or days?

How should I dispose of the solution?  I'm on a septic system out in the country...

Interesting idea......
 
Alex Riddles
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Mike,

Hot dip galvanizing is a simpler process than electro galvanizing. They just clean the steel and dip the part in a vat of molten zinc.  The zinc freezes and sticks to the cooler steel.  So, all we have is steel and zinc not some other chemical bonding agent.  That works in your favor.  Zinc is zinc.  So, deplating will work regardless of the original process.

Hot dip galvanizing typically leaves a thicker layer of zinc. So, removing it will take more time than a thin layer.  How long is a function  of how much zinc you are removing, the chemical reactivity of your solution, and the amperage is your current source.  More amps will speed of the process.  More acid will speed up the process at the cost of more cleanup.  Without knowing the detail of how you set this up it's impossible to know exactly how long.  But, as a wild guess I would think maybe a day maybe a little  more.

As for disposal,  first be sure you neutralize the acid.  That's what the wood ashes will do for you.  If you have litmus paper that will tell if it's neutral solution.  Or stick a piece of rusty steel in the solution acid will clean the surface.  In this case that's a bad thing.  Once the acid is neutralized you have zinc and  sulphur.  Personally I would dump it on the ground.  But, I have a soil test that says I need more of both. There is only a small amount of zinc in solution.  Everything you removed from  the tub will be deposited on that steel cathode.  
 
Mike Jay
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Thanks Alex!  I'll still keep an eye out for a cast iron pot or other option.  But if that fails, it's time to do some chemistry.  Yay!
 
James Freyr
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Hey Alex that's really cool. I didn't know things could be electro deplated. I'm taking that nugget of knowledge with me!
 
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You're talking about food preparation. You don't really want to screw around trying to make something work, for which it was not intended. Instead of spending money to replicate something you saw somebody else do, which really shouldn't have been done in the first place, may not be your best choice. Spend the money and do it right. Get a cast iron kettle. That's what they're for, ...food prep. They are for sale all the time on craigslist. I've seen them often for 50 to $150. Just keep looking in the towns around you until one pops up. If that doesn't work, kettles are sold all the time at antique shops. Even if it looks in poor shape, just sand paper it, wash it, put it over a slow fire and oil it (same as you could do with a cast iron pan). Then you'll have something for making mass quantities of soup, rending lard, making pop corn, and ...parching rice. Keep the cast oiled and it'll last forever. Try to use steel anything and it will rust.
 
Mike Jay
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Good points Jim.  I would only do the wash tub if I can be quite sure I've gotten it down to bare steel.  I'd keep in inside to avoid rust.  The size/shape/weight of the wash tub was perfect for the application.  

I've been watching craigslist and haven't seen any good cast iron near me (within 150 miles).  But I'll keep searching.

Thanks for the advice everyone!  I think I now know how to un-galvanize a galvanized wash tub
 
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I don't know how it's made, but every Ladakhi farming family has a pan for parching barley.

(Photo by Lisa Hornak, apologies in advance to her!)
Roasting-barley-in-Ladakh-by-Lisa-Hornak-2015.jpg
[Thumbnail for Roasting-barley-in-Ladakh-by-Lisa-Hornak-2015.jpg]
Roasting barley in Ladakh in preparation for grinding it
 
Mike Jay
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Oooh, that would be perfect.
 
Rebecca Norman
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They first heat up clean sand, then mix the grains in and stir them around, and then sift them out again afterwards.
 
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An e-bay search for cast iron cauldron brought up quite a few results assuming they're close enough.
 
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It is a simple process, I use it often.
Simply apply Hydrochloric acid to the surface you want stripped.
If the item is a thick piece, and small I will submerge it in a suitable, usually ceramic or glass container, if its bigger or thinner I will paint it on.
Concrete paths etc will be surface damaged, but often I have used it to clean old concrete surfaces.
I normally use 100% strength, but have found dilution helps for finer layers.
YOU MUSt be careful about splashing your clothes because you will have holes in them.
Contact on you skin should be avoided and read any warnings, but I suggest you simply wash it with water.
If I paint it on, I stand down wind because the fumes are bad.

Think about what you are doing, try something small and simple and you will see its effectiveness, simply wash with plenty of water when its complete.
You may get others come on and dump on me about the dangers of the process, ignore them.
I can say if you take to precautions I speak of, anyone complaining in my opinion, just wants to be a naysayer.
 
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you might be well off to get another vessel for your rice parching, go to local scrap yard might find something there for cheap, stainless steel or cast iron i would think would work well.
i have had galvanized bucket get rusted out by leaving ash from wood stove in it and it got rained on for a few months
 
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Rebecca Norman wrote:I don't know how it's made, but every Ladakhi farming family has a pan for parching barley.

(Photo by Lisa Hornak, apologies in advance to her!)[/quote
I, for some reason love the photo you posted. It's worthy of a frame on a mantle . Really cool pic.   Larry

 
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"eating zinc" is what i googled at the start of this reply.  
There are apparently many health benefits from zinc consumption.
 
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If you want to do an acid wash, hydrochloric is the safest way to go.  Hydrofluoric is much more effective, but it's a scary powerful.  The molecules of HF are so small, they can eat right past your nerve endings and you don't even know that you are getting burned.  You'll smell your skin getting eaten before you'll feel anything.  But it does an amazingly quick job of taking that zinc off—much more effective than HC.  So unless you are familiar with working with acids and have the proper safety gear, go with HC, not HF.

Be very careful when adding water to acid if you want to dilute the strength.  Its better to add acid to water.  

You can find hydrochloric acid at any Home Depot or big box store that sells pool supplies.  Its also call Muriatic acid.  Its great for cleaning oil stains off of concrete or just brightening up old tired sidewalks and driveways (it etches the concrete, so use it sparingly) and cleaning metal surfaces.  But understand that once you've taken the galvanizing layer off, it will immediately start to rust.  You can retard rust with a wax layer on the metal, but that'll wear off quickly.  When I worked in a sheet-metal fab shop, we'd use a weak HC acid solution to take that wax off if we were etching mirrored stainless or other highly polished surfaces.  

Rubber gloves and scotchbrite.  To dispose, flush it with lots and lots of water.

 
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