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That White Crust on Your Faucet Is Actually Stone! How Sanpole Wipes Out Limescale in 5 Minutes

2026年11月11日 / Last updated : 2026年11月11日桑子研 Science

That White Crust on Your Faucet Is Actually Stone! How Sanpole Wipes Out Limescale in 5 Minutes

Ken Kuwako, your Science Trainer, here. Every day is an experiment.

Have you ever noticed those chalky white crusts clinging stubbornly around a faucet? You scrub and scrub, but they just won’t budge. Believe it or not, that stuff is basically rock. I tried a cleaning trick on the tap in my lab, and the change was so instant and satisfying that I had to share this little piece of sink-side chemistry with you.

Water Scale Is Actually Rock

Water scale (those white mineral deposits) forms when minerals like calcium, dissolved in tap water, harden into a solid. It’s less like dirt and more like stone, and it’s said to be made mostly of calcium carbonate.

Calcium carbonate is all around us. You’ll find it in chalk, eggshells, and seashells, and the stalactites hanging in limestone caves and even marble are close relatives. In a way, the crust on your faucet is a tiny stalactite, slowly growing right there in your kitchen or bathroom.

Let’s Pour Some Sanpole On It…

I took a bottle of Sanpole, a toilet bowl cleaner popular in Japan, and poured it onto the scale near the sink in my lab.

Sanpole

It reacted right away, and the scale came off so cleanly it was downright satisfying. Take a look at the video!

Why the Stain Vanished: Acid Dissolves Rock

Sanpole contains hydrochloric acid and a surfactant. When hydrochloric acid meets calcium carbonate, the acid dissolves the stone and produces calcium chloride, water, and carbon dioxide. Those tiny bubbles you see fizzing up? That’s the carbon dioxide escaping.

Here’s the key: the calcium chloride that forms dissolves easily in water. The scale started out as a rock that water couldn’t touch, but the reaction turned it into something water-soluble. That’s why, after leaving the Sanpole on for just five minutes, I could simply wipe it away with a rag and the scale came right off. The surfactant helps too, by spreading the liquid across the surface of the stain so the reaction can get to work.

An Acid and a Base, But Not Neutralization

Since an acid and a base are involved, you might guess this is a neutralization reaction, but it isn’t. Neutralization happens when hydrogen ions from an acid combine with hydroxide ions from a base to form water. What’s happening here is different: a strong acid, hydrochloric acid, is kicking the carbonate out of calcium carbonate (a type of salt).

Safety Notes

If you’d like to try this yourself, please keep the following in mind:

Never mix it with chlorine-based cleaners (the ones labeled “Do not mix”). Doing so produces toxic chlorine gas.
Don’t use it on marble or other materials made of calcium carbonate, or on metal parts. It will damage them.
Before using it, check the label to make sure it’s safe for the surface you’re cleaning.

Contact and Requests

Science is more fun when it’s close to home! This blog collects easy science experiments you can try at home, along with tips to make them work. Have a look around and search for whatever sparks your curiosity!
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『高校入試分解問題集理科』（学研）…難しい問題も小さな問題に分解することで、問題を解くことができます。そんな分解の技術が身につくように深く関わりを持って作りました。
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『きめる!共通テスト物理基礎改訂版』（学研）…　高校物理の参考書です。イラストを多くしてイメージが持てるように描きました。授業についていけない、物理が苦手、そんな生徒におすすめです。特設サイトはこちら。

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