HomeDIYHow to Remove Rust with Citric Acid, an Illustrated Guide w/ Pictures
How to Remove Rust with Citric Acid, an Illustrated Guide w/ Pictures
May 15, 2019
In this article I will show you the tools and materials you need to remove rust from old tools, shovels, just about anything. I believe it to be the best method based on cleanliness, environmental, effectiveness, and safety reasons.
I think just about everyone has come across an old tool or antique that has a decent amount of rust. Sometimes there is so much rust that you think it would take hours of polishing with steel wool or sand paper to knock the rust off. In the past I’ve found reasons to not use a tool because it was so rusty, or maybe not purchased an old piece because of the rust.
I decided that the odds of my finding an old vintage number 5 hand plane for little money that was ‘ready to use’ were slim. So, I began researching different rust removal methods. I evaluated a number of different ways, from electrolysis to store-bought rust removal chemicals. Eventually I decided on citirc acid. I found it to be the cheapest way to remove rust with no safety risks, and one of the cleanest methods.
Recently I came into possession of several old vintage hand planes. This was a size that I’ve been wanting for a long time, but never been able to find a good deal on. I swung into an antique store recently and was able to score two number 5 Stanley bench planes for $20. Now, these were so rusty that most people would have thought they belonged on a shelf or mantle for decoration only, never to be used again.
There are many different ways to remove rust
Anyone researching this topic has most likely come across a variety of methods. I’ll briefly describe some different methods here, and give some pros/cons.
A simple razor scraper /sandpaper / steel wool. Any of these can knock off a lot of surface rust from metal without damaging it much. You just need to use some elbow grease. It helps if you lubricate the piece with oil (for sandpaper/steel wool), as it will reduce clogging.
Pro – cheap, clean
Con – time consuming, can’t get to corners
A grinding wheel, or angle grinder. This works quick, but will remove base metal if you aren’t careful. Also, you will need some protective equipment – face shield and dust mask.
Pro – very quick
Con – will likely remove good metal from the parts
Chemical Removal, purchased from stores. The big box stores sell various rust removal products. These are simple to use and are safe/clean. But they cost around $15 per gallon. So if you are doing many parts, or larger parts you might end up spending a bit of money, as you often use a lot more than you think. Additionally, this can make micro-pitting of the metal, giving it a dull, gray finish if left in too long.
Pro – quick, clean
Con – Expensive if doing more than a couple parts, can change finish
Citric Acid. Citric Acid can be relatively cheap, considering that 10 lb costs around $20. And you only need to use about a quarter pound for several gallons of water. But it is clean, biodegradable, safe, and has other uses as well. It can get into all nooks and crannys. The only drawback is that this can also create some micro-pitting in the metal, just like off the shelf chemical removers.
Pro – clean, quick, safe
Con – can change finish if misused.
Electrolysis. This requires some materials up front, but is a really nice way to remove rust. It utilizes electrical current to knock the rust off, and can get into every nook and cranny. You need a number of items, a car battery or charger. Some washing soda, bucket, water, etc. You will be working around electricity and water. But if using a battery, as long as you don’t spill water on the batter it should be fine. However, this method has a longer set up and cook time. This is also a method that you would want to keep children away from. Furthermore, this method will produce hydrogen gas, which is flammable. So you need to do it outdoors.
Pro – effective
Con – Messy, larger effort to set up
Why use Citric Acid over other rust removal techniques
I like Citric Acid since it is a clean way to remove rust, cheap, and I can use the citric acid for cleaning and canning. So this method becomes cheap when considering the other uses I can get from the acid powder.
I like the fact that it is non-toxic, is obviously biodegradable, water soluble. So my clean up is dumping the water, and giving the container a quick rinse. The only real drawback I have with it is that if you have any hang-nails or paper cuts on your hands, well, it is going to sting. So I just put on a pair of rubber gloves before putting my hands in it.
Citric Acid Rust Removal – Materials Required
You should gather the following materials for this process;
A bucket, tub, or container that is large enough to submerse your parts
WD-40 and some sturdy paper towels, or shop towels
Citric Acid – you really only need about 1/4 cup to 1 cup, depending on what you are doing. But buying in bulk saves some $$$ and allows you to use extra for cleaning, or future rust removal
Something to scrub the parts that won’t damage them. I used a toothbrush for most, and a stiff plastic-bristled brush for a lot too. A scouring pad or steel wool could work too. Rubber gloves can be nice to have if you have any small cuts on your hands, as the citric acid will sting.
3-in-1 oil, or mineral oil
How to Remove Rust using Citric Acid
Here is my process for removing rust using Citric Acid
Clean the parts with WD-40. WD-40 is a degreaser, so this will remove any build up of dirt and grime. It can be helpful to disassemble your parts (if necessary) so that you isolate the metal components you want to clean up. Grease, oil, dirt can act as a barrier between the citric acid solution and the metal, so you are just trying to remove that.
Fill your container with hot water. Just fill it up enough to submerge the part, or area you want to remove the rust. The hot water will make the acid dissolve quicker, and also have the rust dissolve quicker too!
Add citric acid. I generally use about a 1/2 cup to 1 cup per gallon (20 g to 40 g per liter). Stir until it is dissolved.
Submerge the parts. Just place them in the solution. I give them another scrub once in the solution to make sure there are no barriers between the solution and the rust.
Monitor the solution. Watch it to see that small bubbles are forming. The bubbles tell you that the solution is working. If after 15 minutes you don’t see any bubbles, consider adding a bit more acid.
Periodically scrub parts while they soak for 1 hour. Wait. Scrub. Wait. Depending on the level or rust, it could take an hour or two. I periodically scrub the parts to help knock off any rust. Actively monitoring the parts also will allow you make sure the ‘good’ metal on the parts don’t start getting too much pitting. So, use common sense when doing this.
Dry and oil the parts. Once you are satisfied with the rust removal, remove the parts from the bath and dry them immediately. Then, immediately after drying give them a healthy coat of 3-in-1 oil. The 3-in-1 oil will prevent flash rust from forming on the parts after removal from the bath. If you skip this step you will likely get a fresh coat of surface rust on the parts within a day.
To clean up, dump citric acid down the drain. Rinse the container to remove all the particles. But citric acid solution is completely safe and biodegradable.
Also, here is a brief video showing the overall process. It is only a couple minutes long, but you can see it all in actions.
Here are some pictures of the before/after of these handplanes. I wanted to make sure I didn’t negatively effect the finish on these, so I was mainly concerned with surface rust. But I am quite pleased with the results.
This depends on how much, and how deep the rust is. If it is just surface rust, a normal citric acid solution could remove it in 20 minutes. If the rust is deep, then it could take a couple hours. However, like most rust removal methods, it can change the finish of the ‘clean’ metal if left in the bath too long. So take good precaution, monitor it, and use good judgement. You could always polish with fine wet/dry sandpaper though.
Is citric acid biodegradable?
Yes. Totally safe for the environment.
Is citric acid safe?
It would hurt if you got it in your eyes. It will also make small cuts on your hands sting (think lemon juice).