Saturday, April 28, 2007
Things Not To Do With Hydrochloric Acid
Last Tuesday I took the day off to plaster the walls in our bedroom. My father came over to help me in the role of Main Assistant Plaster Manufacturer. He made the plaster, I smeared it on the walls. Together, we put some 150 kilos of plaster against the walls, in a layer of half a centimetre, and after a day’s work we were only half way there.
Anyway, when I had finished some of my tools were caked with hardened plaster. I started to scrub it off with water, but that’s not much use when the stuff has already hardened. So how could I get it off?
‘Ah’, I thought, ‘chalk dissolves in acid!’ That is how you get limestone caves: the chalk dissolves because of the slight acidity of ground water.
So I tried common vinegar, but the effect was not dramatic. In fact, it didn’t do squat. But then I remembered we had stronger stuff in the house: hydrochloric acid. So I filled up the sink with water, plunged my tools in and added some HCl. For the record: I did put on rubber gloves – safety first!
It worked like a dream, most of the plaster dissolved right away. Only my big plastering board was still covered in loads of hardened plaster. It has small depressions in it so the plaster won’t slide right of if you tilt it, but these were filled with hardened plaster which was very difficult to remove.
So I left it to soak for a night. The next morning, I forgot about it, so it soaked a bit further. And the next night too, because I can be very absent minded sometimes. Make that always. What was I talking about? Oh yes, the plastering board.
The board was fine, and completely plaster-free! Hooray!
It was the sink that was messed up. It’s an aluminium (or possibly stainless steel) sink, and apparently the chemical reaction between the plaster and the HCl caused the metal of the sink to darken. So now we have an etched sink, with dark spots all over. Luckily it’s an old sink, scheduled to be dumped when I install the new bathroom. But still…