How do you dissolve plaster of paris

  1. We have purchased a federation style home, which had the front painted white. During the removal process, we found that underneath several layers of paint, plaster of paris had also been applied in a random way, and is proving very hard to remove. We have tried HCL, as spirit of salts, but no luck. Also tried a caustic paste, but it still won't shift. Any product would have to be readily accessible, and relatively cheap. The house isn't that big, and it only the front of the house, but there are still alot of bricks that need plaster removed. Any ideas?
    Last edited: Jan 27, 2011
  2. jcsd
  3. Last edited: Jan 27, 2011
  4. Thanks Kracatoan, we will try it over the weekend.
  5. Can you rent a sand blaster?
  6. Borek

    Staff: Mentor

    Don't believe in acids. Muriatic perhaps, but even then I would not expect outstanding results, and it can eat through everything else first. Sadly, as far as I know scraping is the best option.
  7. Hmm, if it were up to me, I'd apply 30% Hydrogen Peroxide or Perchloric acid then follow it up with some Hydrofluoric Acid. That's asking for a pandora's box of trouble though. Also, it may require some kind of portable microwave generator for best results... :)
  8. Borek

    Staff: Mentor

    When I think about the results I think it would be easier and safer to rent a bulldozer.

    Don't forget to insure the house before trying.
  9. I am so surprised that the people on this forum, and other forums, obviously don't have a clue about the chemistry of plaster of paris. I read in so many places things like "uh, try some kind of acid..."

    So I have a lot of concentrated chemicals on hand and did lots of experiments with all kinds of acids, both dilute and concentrate, under many conditions and determined that acids do not dissolve Plaster of Paris in any way, but sometimes make it harder.

    The chemicals which dissolve plaster of paris are on the basic end of the PH scale, not acid. I first had some success with potassium cyanide, but what really worked better than anything is Sodium Bicarbonate. Makes sense. The sodium in baking soda hooks up with sulfur in the plaster, and the carbon hooks up with the calcium in the plaster.


    Don't use any acids or it will only defeat the process.

    Now what really amazes me is that the answer is so simple and safe, and surely some people must know it, but it apparently cannot be found on the internet, until now.
    Gypsy Moonlight likes this.
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