Electrolytic Rust Removal
Taking off rust, grease and paint with a battery charger
© Copyrighted by
I know you’re anxious to get down to the nitty gritty and find out how to take off rust; but, we’ve got to cover the important stuff, first. That is: you, your eyes, and your health.
Be careful! You’ve only got two eyes. Protect them. Although electrolytic rust removal can be done with nothing more harmful than clothes washing detergent, there are times when you may want to take the process one step further and end up with castings that look as if they just came out of the foundry. This might require the use of acid. Some electrolyte recipes call for lye, so you might use it, too. If you get acid or lye in your eyes you can be blinded. Don’t let this happen. Protect your eyes with goggles and your skin with a full face shield. It’s the smart thing to do.
Certain acids can produce some harmful vapors and you should avoid inhaling them. In particular, hydrochloric acid (muriatic acid) should be used outdoors or under a ventilating hood (not found in most shops). Always stand upwind from the acid as it reacts with the piece being de-rusted.
Rubber gloves are inexpensive. You cannot afford not to use them. Harbor Freight sells latex and Nitrile gloves in boxes of a hundred. On sale, they run about $6 or $7 per box.
You should also have a supply of fresh water for flushing off spills. Whether it’s delivered via hose or bucket, have some on hand.
Electrolytic rust removal generates hydrogen gas. Hydrogen is flammable and it has the widest explosive range of any fuel gas. Set up your de-rusting vat outdoors.
You can keep your electrical power supply (battery charger) indoors and run the cable through a door or window to your electrolysis vat. If you set your battery charger outside, protect it from rain and lawn watering. But, don’t cover it with a box or bucket. If tightly covered, it is liable to overheat and burn up.
None of this is meant to scare you. It’s just common sense. You’ll be using chemicals that can be purchased in most paint, plumbing supply shops and grocery stores.
An electrician once told me he wasn’t afraid of electricity; but, he had a lot of respect for it. It’s the same way when handling strong acids or bases (lye). You don’t need to be afraid of them, just respect them and handle them accordingly.
Be careful with what you do with discarded leaded paint, toxic solutions, acids, or bases. They can create an environmental hazard. You’re not a tree hugger and don’t care? Well, if you dump some of this stuff on your property, it might hit you in your pocketbook when it comes time to sell.
If you use electrolytic de-rusting as part of your business operations, any waste you dispose of will have to comply with environmental laws and regulations.
Household wastes are exempt from hazardous waste disposal requirements; but, common sense applies. If you have any question, contact your state’s environmental office.
I’ll go into this more, later. You’re anxious to get started, so let’s go.
Fact #1: Water is a poor conductor of electricity.
Surprised? Well, it’s the truth. You may know the dangers of electricity in your bathroom, but it doesn’t take much electricity to kill you. Electrolytic cleaning takes thousands of times more current than what will kill you.
So, we need to mix up some electrolyte that will conduct electricity. There is nothing magic about washing soda, baking soda, lye, tri-sodium-phosphate, or anything else that is used for an electrolyte in de-rusting. The big picture is this: You’re merely mixing up a solution that will conduct electricity. That’s it. Period.
Now, don’t get ahead of yourself and say, “Hey, I’ve got some rock salt. A mix of water and salt will conduct electricity.”
Fact #2: A basic solution helps prevent iron from corrosion.
You can think of a “base” as being the opposite of acid. Lye is basic. It has a pH between 7 and 14. When certain harmless substances are dissolved in water, they will also form a solution with a pH between 7 and 14 (high pH).
Washing soda (sodium carbonate) and tri-sodium phosphate (TSP) will create a high pH solution when dissolved. (They are not actually bases, but their solutions will have a pH between 7 and 14.) Lye is sometimes called for in electrolytic solutions. Lye, (sodium hydroxide) is a powerful base and is very harmful. Handle it with care! Wear protective gear!
Fact #3: An electrical current is a flow of electrons.
The electrolysis process supplies electrons to hydrogen ions in water, changing them into hydrogen gas. More current = more hydrogen. More current = faster de-rusting.
The amount of current your setup draws depends upon the following:
· Power supply voltage—More volts, more current.
· Size of workpiece—Larger workpiece, more current.
· Size of “waste” electrode—Larger waste electrode, more current.
· Workpiece/waste electrode spacing—Shorter distance, more current. Longer spacing, less.
· Strength of solution—Stronger solution, more current.
Finally, down to the nitty-gritty
Here is how to de-rust with a battery charger
1. Find a plastic container big enough to hold your item to be de-rusted. (There’s nothing magic about plastic. Again, the big picture: The important thing is that it doesn’t conduct electricity, corrode, and spring a leak.) Plastic 55-gallon drums work very well. Hint: Don’t cut out the top. Make a wooden cradle for it to lay on its side. Then, cut a foot-wide slot the entire length of the drum. You’ll be able to de-rust much larger things this way. Example: Cleaning buzz saw blades, ½ at a time.
2. Mix up a solution of Arm and Hammer Washing Soda and water. Can’t find Washing Soda at your grocery store’s detergent section? Then, use Arm and Hammer “FabriCare.” It has sodium carbonate in it. All you want to do is make an electrolyte that conducts electricity. The FabriCare is a nuisance because of all the suds it makes, but if you can stand its perfume, it will work just fine. The 2.94-pound (18 Loads) size will be just right for a five gallon bucket of solution. How much washing soda? It’s not terribly important. Use plenty. This will be discussed, later.
3. Find a “waste” electrode. A chunk of plate steel will work, but it will quickly turn your electrolyte into a rusty mess. If you can find any, graphite works very well and will not cause an environmental or toxic hazard. It will also leave your solution relatively clean. Size? It’s not terribly important; but, if it’s too small, you won’t get much current. Start out with something that’s about the size of a license plate. (But don’t use aluminum license plates! They won’t last!)
4. Hang your waste electrode in the vat of solution. Connect your battery charger’s positive (red) lead to it. Keep this connection out of the solution. If you don’t you’ll ruin your charger’s alligator clip. A 1”X 2” wooden stick laid across the top of your vat makes a handy way of supporting your waste electrode. Drill a hole in your electrode and hang it with a wire or stout nylon string.
5. Remove all aluminum, pot-metal, or “foreign” metals from your iron/steel item to be de-rusted. Aluminum and pot-metal will be ruined. In my experience, brass, copper, and bronze pieces are not seriously harmed; but, don’t take my word for it. The tin in brass will etch out of the surface and leave brass looking like copper. It is best if you remove that priceless only-one-in-existence nameplate. YMMV (Your mileage may vary.)
6. Take your piece to be de-rusted and file the rust off a spot. This will be for making good electrical contact. Then, connect your battery charger’s negative (black) lead to it.
7. Hang your workpiece in the solution. It’s best to support it with a piece of wire hanging from a stick. This keeps it out of the sludge that will eventually pile up in the bottom of your vat.
8. Make sure the waste electrode is not touching your rusty part. The distance of separation isn’t terribly important. More on that, later.
9. Set your battery charger to the 6-volt range.
10. Plug in your battery charger and turn it on.
11. Check the current draw. Six to 10-amperes is a good range to shoot for. If your ammeter doesn’t show any current, check your connections. If they’re good, move the waste electrode closer to the workpiecc. If that doesn’t work, switch your charger to the 12-volt range. If that doesn’t work, mix up a stronger solution.
12. If the current draw is too high, it can burn out your battery charger. To reduce it, you can do any of the following: Use a smaller waste electrode; pull the one you have partially out of the water; move the waste electrode further from the workpiece; add water to dilute the strength of your solution; switch to a lower voltage range.
13. Let the process work. Come back a day later and pull your (previously) rusty piece out of the solution. It should be black. If it’s still rusty, you haven’t made good electrical contact to it. This can happen in assemblies. The rust is preventing electrical contact between the parts. Note: Sometimes, if the rust was really thick to begin with, you might find a layer of red rust on top of the black crud. This is just fine. The red layer will float right off with a light wire-brushing.
14. Check your progress. Turn off your charger, pull your part out of the water, and try wire-brushing the black crud off. It actually won’t come off until you rinse it; but, give it a good brushing and then rinse it off. (Scotchbrite pads will work well in getting off the final traces of black crud.) If you’re lucky, you’ll see bare iron. If not, put it back into the vat.
15. When your part comes clean after brushing and rinsing, let the part dry or blow off the excess water.
16. Your part will probably look great for a while; but, almost before your eyes you may begin to see a reddish tinge of rust re-appear. You can get rid of this with a passivating agent, described in the following steps.
17. “Passivate” the surface with Jasco “Metal Prep,” Ospho, or any similar phosphoric acid and metals salts preparation. It’s available at most paint stores and in the paint department of some hardware stores.
18. If your part is made of cast iron, take a clean lint-free paper shop towel and immediately wipe off the excess passivating agent. If the part is steel, the reaction will be much slower. You can either wait about five minutes, then wipe off the excess; or, you can let it dry. The choice is yours.
19. You’re done!
Does this all sound too complicated? Well, take it from a person who has a bead blast cabinet and a pressure pot abrasive blaster, electrolytic de-rusting is faster, cheaper, and easier than abrasive blasting. I’ve had my electrolytic vat in almost continuous operation for the past seven years. Rather than stand at the bead blasting cabinet for days on end, my de-rusting operation keeps going while I sleep and go on vacation.
If you don’t immediately prime and paint, the passivation process is something you should do after abrasive blasting, anyhow. So, it’s not any more work to do it as suggested, here.
If you don’t passivate, you’ll notice some red rust forming soon after you are done. This is what happens: Some of the rust was converted back to pure iron, but it is in the form of very fine particles. This fine iron “dust” will almost immediately re-rust. The passivation process removes the last traces of rust and prevents re-rusting.
Some people suggest using phosphoric acid for passivation. Take my word for it, if you use phosphoric acid, you’ll eventually wind up with more rust than you started with. Been there. Done that. Use the phosphoric acid mixed with “salts” that is intended for the job. It doesn’t cost any more than straight phosphoric acid; and, it is more readily found in stores.
As mentioned, earlier, most paint departments sell compounds made of a blend of phosphoric acid and certain metal salts. Sometimes they are called “metal etch” compounds. They are all very similar, but some seem to work better than others. I prefer the “Jasco” Metal Prep brand, however, the only place I’ve found it is in a Seattle Home Depot. Local Home Depot stores don’t carry it.
“Ospho” is readily available in these parts, but in my experience it tends to remain “sticky” instead of drying completely. Ospho directions say that it can be used as a primer, but I have reservations about painting on top of a sticky surface.
To avoid the sticky surface, I apply Ospho sparingly. If the part is cast-iron I immediately wipe off the excess with a blue paper shop towel. If it’s steel, I’ll either blow off the excess with shop air; or, wait five minutes and wipe off the excess. Use eye protection and wear coveralls if you blow it off.
Another way of preventing a too-thick layer of these passivators is to apply them, let them “work” for a few minutes, then rinse off. Then, immediately blow-dry with shop air.
I have tried diluting these passivation products, but have gotten unsightly results. The end result will be a layer of white powder. The directions instruct the user to brush off the excess white powder; however, I don’t have confidence about paint sticking to it very well.
If your rusty piece is stubborn about coming clean, finish up with either hydrochloric acid (muriatic acid, available at your plumbing shop or hardware store), phosphoric acid, Rust Solv, or you can abrasive blast it.
If you use hydrochloric acid, your part will look nice for a few days, but will soon show signs of rapid rusting all over, again. You can prevent this by following up the acid cleaning with another day of electrolysis treatment. The electrolysis will help remove all traces of the troublesome chlorides.
Be careful with hydrochloric (muriatic) acid! Follow all precautions given in the introduction. As mentioned in the previous paragraph, follow the acid cleaning with another electrolysis session. Then, passivate the part with Ospho, or the like. If you don’t repeat the electrolysis after using acid, you’ll wind up with rust that is worse than before. [Have you ever seen the rust caused by salt (sodium chloride) or tractor tire fluid (calcium chloride)? Well, any remaining traces of hydrochloric acid (hydrogen chloride) will do the same thing.]
If you use hydrochloric (muriatic) acid, store your supply outdoors. Even in a closed container, it can rust everything in your shop! Been there. Done that. I keep my jug in a five gallon bucket, outdoors.
Even if you have to abrasive blast, you’ll find that by electrolytic de-rusting beforehand, the time you spend abrasive blasting will be a tiny fraction of what it usually takes. Furthermore, your grit will stay cleaner, longer, because most of the rust was removed beforehand. Without all the rust dust, visibility will be much improved in your bead blasting cabinet.
More about “waste” electrodes
Some people will suggest using stainless steel for waste electrodes. They claim that the stainless will not be affected. Not so. Been there. Done that. I have proof. It started out as a medium-gauge piece of solid material and is now a paper-thin sheet of stainless steel that looks like a lace curtain.
You will find that stainless steel waste electrodes will last much longer than ordinary mild steel. However, be prepared to deal with a poisonous waste, afterward. You’ll eventually notice that your solution will turn yellow and the stainless steel is disappearing. The yellow is caused by the presence of chromate. Hexavalent chromium is poisonous. Please don’t ruin your property by dumping it on the ground. Please don’t dump it down the drain.
I am a “householder” and not a business; however, I am careful of how I dispose of my chromate-bearing wastes. I evaporate the solution in the summer sun until is completely dry. Then, I take the dried rust/chromate sludge and deliver it to one of the special collections of hazardous waste. Your local landfill or state environmental quality office will tell you the time and place.
much better waste electrode is graphite.
The last time I was there, Pacific Recycling at
But, steel works very well, except that it makes for a very messy, rusty solution. If you have to leave your part in the vat for a long time, you’ll find that rust particles will settle out on it, making a mess that you’ll have to brush off.
As mentioned, earlier, the purpose of the “stuff” dissolved in the water is to make a solution that conducts electricity. Don’t worry about recipes for your electrolyte. It’s not like baking a cake, the ingredients are not critical.
Whatever you use for mixing your electrolyte, it never “wears out,” but contaminants may eventually make it unusable. For the most part, all you need to do is replenish the water as it evaporates and is converted to hydrogen gas. But, if the solution gets loaded with dirt, your part may be disappointingly dirty after electrolysis. At that point you may want to dispose of it and mix fresh. My electrolyte generally lasts a year, or more.
You should cover your vat with a loose-fitting screen to keep out insects, leaves, and pets. Do not cover tightly! You don’t want to accumulate an explosive volume of hydrogen gas!
There’s at least one recipe out there that calls for a heavy dose of washing soda. It would be prohibitively expensive to follow it if mixing up a 55-gallon batch. I find that one 3½ pound box of washing soda and an 18-ounce container of Red Devil lye is plenty for a 55-gallon batch.
This is a fairly “weak” solution, but with it I can easily pull maximum current on my battery chargers if I use a foot-square waste electrode.
In our dry climate, strong solutions are a pain. You’ll have to deal with a white crust at the waterline of your vat and workpiece (if it isn’t fully submerged).
Here is one such recipe for a strong solution of one gallon:
Washing soda 10-oz.
Tri-sodium-phosphate (TSP) 3.3-oz.
Water glass (sodium silicate) 1.7-oz.
Multiply it out and you’ll find it would require almost ten boxes of washing soda for a 55-gallon batch!
That said, however, the strong solution may make a more effective de-ruster. Under the white crust at the waterline where the “strength” of solution is strongest, I usually find clean, bare metal.
With a gas tank there will be these problems:
· Getting a big enough “waste” electrode inside it. A steel rod will work, but the process will take longer because it won’t have much surface area.
· Keeping the waste electrode from shorting out to the tank. I use pieces of rubber hose, wraps of rubber bands, plastic window screen, coffee can plastic lids, wood, etc. for this. Just remember that solid barriers, such as a plastic lid, may prevent the current from reaching the area underneath. That’s why plastic window screen works well.
· Preventing the accumulation of explosive hydrogen gas. This is easy. Just make sure the tank is completely full of solution.
· Getting rid of the cruddy residue. A good shaking with the tank partially filled with water and crushed gravel does a good job.
One job I had was to clean the rust off a cylinder wall. I poked a collar of plastic in the spark plug hole, then poked a steel rod through that. Then, I took a plastic lid the same size as the bore, punched a hole in it, and slid it over the rod inside the cylinder. All these precautions keep the waste electrode from shorting out to your workpiece. Most battery chargers have some kind of circuit breaker to protect them, but there’s no use of risking fire or burning up your charger. Be careful
For this technique to work, an electrical current must be able to “reach” the rusted area. But, in the wee, tiny gap between a piston and cylinder, it is unlikely to happen. Even if this area could be “wetted” with the solution, the surrounding area will “soak up” the current and create a shield that pretty well prevents large currents from getting down into the gap.
I’ve found many engines to be stuck from varnish and dried out carbon. It forms such a strong barrier to the solution that it is unlikely that electrolysis will work. That said, however, if all else fails to unstick your engine, it’s worth a try. However, be sure to dry out the engine after pulling it from the vat. You don’t want to create further rusting or corrosion by leaving water in the cracks and crevices.
You can clean many parts at once. The only thing you have to make sure of is that they are all connected together, electrically. I usually string them on a length of bare copper wire. The copper won’t be affected.
There’s no problem if one doesn’t connect up, electrically. There will be no harm done. Just file off some rust, make a good connection, and give it another day in the vat.
All but the best of paint jobs will lift off in big sheets. It will amaze you. Remember, you will probably find leaded paint on antique machinery. If you are a business, you’ll have to dispose of it as hazardous waste.
If you are a homeowner, common sense applies. Do the right thing.
Brushing off the black crud
Ordinary wire brushes work well, but they can’t get into nooks and crannies. For this, use the small wire brushes with a looped handle and are shaped like paint brushes. They are found at most welding supply places.
After wire-brushing, you may want to follow up with a rubdown with a Scotchbrite pad, followed by a rinse with water. Then, blow dry with shop air.
deposit on plastic 55-gallon drums is about $25.00 so this is what most oil
distributors charge for them. D&B
Farm and Home Supply in
As mentioned, earlier, you’ll be able to de-rust bigger items if you cut a foot-wide slot in the side. The plastic is flexible, so you can temporarily spread this slot to get much larger things into the vat. I’ve de-rusted entire engines.
Really big stuff
If you put large items, such as buzz saw blades or flywheels, into your vat, you can de-rust one side, brush off the crud, then put the other half and de-rust it. There is a “however,” though. You might wind up with a visible line at the high water mark. It’s merely a cosmetic thing and shouldn’t show after painting.
Any unused acids or passivators can be stored in plastic cottage cheese or sour cream containers. They come with a tight fitting lid. So, you shouldn’t ever have excess acid to dispose of. Whatever you do, don’t dump it on the ground or throw it down the drain. Use it until it is gone.
If you must dispose of acid, neutralize it with ordinary lime. Then, you can safely dispose of it in the garbage.
It’s a good idea to have lime on hand to neutralize any spills. Acid will cause serious etching of concrete, so keep it off your floors, driveways, or sidewalks.
My favorite setup
I cut a twelve inch wide slot the length of a plastic 55-gallon drum and laid it in a wooden cradle. I added one box of washing soda and a can of lye.
At each end of the drum I’ve fastened a large waste electrode. For small jobs, I connect both to one battery charger. For big jobs that would overload one charger, I’ll connect one charger’s positive lead (red alligator clip) to each waste electrode. Of course, you should connect all negative leads (black) to the part to be de-rusted.
What can go wrong
So, you set up your de-rusting operation and everything seems to be going just fine: The battery charger’s ammeter shows a good, healthy current, tiny bubbles are fizzing up from the part you’re de-rusting. Everything looks great!
But, a day later you take a look and there’s no current, no bubbles, and your part is just as rusty as it ever was. What’s wrong?
Nine times out of ten you’ll find that you’ve got a bad electrical connection, somewhere. If any connections to your waste electrode got down into the solution, it’s almost certain that corrosion stopped the flow of electricity. Just file or sand off the gunk, make a good connection, and things will be just fine, again.
Most battery charger alligator clips have a rather cheesy crimped connection between the wire and the clip. Eventually, there will be some corrosion there and the electrical resistance will increase. When this happens, the connection will overheat, sometimes to the point where the insulation will melt. Keep a close watch on this connection. If it starts going bad, use an awl to spread the crimp and disconnect the wire from the clip. Use sandpaper to clean things up and re-crimp. You may want to solder this connection like it should have been in the first place.
You might also want to check your waste electrode. If you used a flattened tin can like I did the first time, it will probably be gone! Yup, with great care I cut both ends out of a 3-pound coffee can, figuring I had a great waste electrode. In a day it was gone!
How long can you leave something in the vat?
You’ll read later on about a post drill that was left in the vat for three weeks. But, if your solution is really rusty, you won’t want to leave your things cooking too long. The rust will settle out on top of the thing you’re trying to de-rust. It will look worse than when it went into the vat. Actually, the rust won’t be fastened to your part; but, it can be a nuisance. Sometimes, it doesn’t want to wire-brush off.
What you’ll want to do is remove the stain with hydrochloric (muriatic) acid. It will come off rather easily.
But, the best thing is to not forget and leave your part in the vat too long. It won’t be damaged; it will just be a bit harder to clean up.
Electrolytic de-rusting isn’t the end-all, do-all. It has its place. There will be times when you can’t use it. It sometimes won’t touch the “skin” on some castings. Quite often this is a mix of sand and gunk. Pieces that have been badly scorched in a fire can also have a skin that won’t come off. Don’t worry about it. If it’s stuck that tightly, you can probably paint right over it.
That said, however, this process usually works very well on cast iron. It works less well on some steels. Why, I don’t know. Very often it won’t get down into rust pits.
You’ll hear some folks say that the process is “line of sight.” That is, only the side of the part that faces the waste electrode will be de-rusted. To a certain extent, this is true (more on that, later). But, you can say with 100-percent certainty that it cannot “reach” into “shielded” places such as gas tank interiors.
Gas tanks, carburetor bowls, and other enclosed castings present a challenge, but they can be electrolytically cleaned. Just wrap the waste electrode with plastic window screen (to prevent it from shorting out), and put it into the gas tank or whatever. Window screen, rubber bands, wooden sticks, scraps of plastic milk jug—you name it—will come in handy for these jobs. Just use them, as necessary, to prevent the waste electrode from accidentally shorting out to the workpiece.
“Line-of-sight rust” removal?
Many electrolysis instructions will tell you that the process is “line-of-sight.” That is, rust will only be removed from the side of your part that faces the waste electrode.
When I first started using this process I noticed the line-of-sight thing. In the years since, when I use electro-de-rusting, all sides of the part come clean. The only exceptions are shielded pockets or nooks and crannies.
I wondered why my experience was different from others; and, I wondered why I experienced line-of-sight then, but not now. I think I’ve discovered the answer.
When I first experimented with electro-de-rusting my container was a one gallon ice cream bucket. Then, I moved up to a five gallon bucket. Finally, I settled on using a fifty-five gallon barrel.
Aha! That’s it! The large barrel allows a large “field” of voltage to surround your entire part. Thus, all sides of your part get de-rusted all together.
Contrast this to using a small container. There is not enough space around your part to allow a large field of voltage to develop.
I can demonstrate this “voltage field” effect, easily, by moving the waste electrode from the side to the middle of the vat. By allowing a large space around the waste electrode, the back side of it became “electrically involved” in establishing a connection to the solution. The same effect occurs at the part being de-rusted.
Some success stories
Post drill #1. Found in a junkyard. It had been in a fire and was a total wreck. Hopeless. Every nut, bolt, and set screw was seized up, solidly. So, I paid 15¢ a pound for it and dropped it into my vat while I went on a three week vacation.
When I got back every fastener came off without a struggle. Except for the flywheel which suffered some scaling, every part cleaned up and looked as if it just came from the foundry.
Post drill #2. Found in an antique store. As well as being rusty, it had a half-century of hardened grease and crud one it. The whole works went into the vat for a few days.
Every speck of grease and loose paint floated to the top of the vat. This one cleaned up without dismantling. I only had to blow out all shafts and bushings with air in order to dry them out and prevent re-rusting.
Feed grinder. The burrs, shaft, and all fasteners were seized up, solidly. Into the vat it went.
Everything came unstuck. No harm was done to the babbit bearings. It cleaned up, beautifully. Try doing that with a sand blaster!
Copyright © 1998-2008, Orrin B. Iseminger
Revised -- 12/23/08