Bathroom Buildup Is Calcium Carbonate

I would like to bring to your attention an inaccuracy that occurred in the April 24 Real Estate section, “That Crusty Bathroom Scum Is Actually a Buildup of Lime.” In it, it is stated that the scale or lime building up in bathrooms and kitchens is calcium oxide. This is incorrect. Calcium oxide is very reactive and very caustic. It reacts vigorously with water, and will dissolve without too much effort. The scale or lime that builds up in bathrooms is calcium carbonate, which is not soluble, but is also not at all dangerous. The confusion probably comes because calcium carbonate is often called limestone, while calcium oxide is often referred to as quicklime, and both are often shortened to lime.

KEITH RICKERT

Pasadena