Do you remember asking the classic question in high school chemistry class: “When am I going to use this?”
I confess that I was one of those who asked this question loudly enough that I was rewarded with an afternoon of detention. It wasn’t until years later that I realized how much simple chemistry surrounds us in our daily lives.
Let’s talk about oxalic acid, a fairly safe and affordable organic compound that you can use to remove rust from clothing or concrete, vinyl siding, or vinyl pool liners. It can also remove tough tannin stains from the bottom of boats.
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I became aware of oxalic acid decades ago when I started Ask the Builder. I was looking for the best way to clean redwood. The California Redwood Association sent me a wonderful brochure explaining a step-by-step method to make dark, dark redwood look new again using an oxalic acid solution.
Not too many years later I learned that oxalic acid can solve a different problem. A reader had written to me about removing rust from concrete. I asked a chemist friend for advice and he said, “Oh, that’s easy; use oxalic acid. I shared the tips and heard the reader say it worked well.
However, years passed before I tried it myself. Just a few weeks ago a rust problem appeared in my house. The most used toilets in our house have started to have nasty rust stains in the bowl. Then the rust spread to our white porcelain apron kitchen sink. A week later, a second toilet bowl began to develop a slight orange cast.
I contacted the company that installed our water softener and purification system. The first question the rep asked was, “When was the last time you changed the filter?”
The filter in question captures dissolved iron in our well water. It should have been changed months ago, but I forgot. I flinched when I saw the state he was in. (I’m far from perfect in housekeeping, as my lovely wife regularly reminds me.)
Once the water system was working properly again, I set up an automatic schedule reminder so that every three months I get an early morning reminder to change the filter.
Now was the time to tackle the cleaning of porcelain surfaces. I ordered a two pound bag of oxalic acid crystals. When it arrived I read the warnings and instructions. Following the instructions, I poured a tablespoon of white powder (which is almost the same as icing sugar) into the toilet bowl that had the fewest stains.
I used the toilet brush to agitate the water slightly so the oxalic acid powder dissolved. It did it in seconds in room temperature water. Within minutes, the light orange stains began to fade. I used the brush to spread some of the acid solution on the sides of the toilet bowl where two vertical spots extended from the holes in the rim of the bowl.
After a few more minutes, the bowl looked brand new. The transformation was almost unbelievable. Since we have curious cats, I made sure to never leave the toilet unattended during this process. If you have pets and need to let the oxalic acid sit longer, be sure to lower the toilet seat and close the bathroom door. Put a sign on the closed lid warning other humans that an acidic solution is in the bowl.
After that win, I went to the garage to see if oxalic acid would remove the hard rust stains left on the concrete floor from the bottom of my snowblower. I decided to increase the strength of the solution by adding two tablespoons of oxalic acid powder to 6 ounces of water. I put the plastic cup filled with water in the microwave to warm it up before adding the acid. I remembered from chemistry class that heated water would make the powder dissolve faster. I was not deceived.
I took a photo of the rust spots before I started. I then poured the acid solution into the center of the worst rust area to create a puddle. I wanted to be able to see the original rust spot on either side of the test area after this experiment is complete. Keep in mind that I didn’t scrub or do anything other than pour the solution onto the concrete.
I let the acid sit for hours, and later when I went out to use the grill to cook, I used plain water to rinse off the acid solution that was left and scraped it off . The next day a large amount of rust was gone and the concrete looked much shinier. I know I can remove all the rust with a little more effort and my concrete floor will look brand new!