Wear a mask, gloves and glasses. Using the wire brush, remove all the salt from the walls of the house. Immediately afterwards, pour one glass of hydrochloric acid and three of water into a container and mix with a brush.
Spread the solution with the brush. Don’t be afraid if you notice a kind of foam: it is the result of the effect of the acid on the saltpeter. Let sit for 5 to 10 minutes, then scrub the wall with soap and water. Rinse and dry with a clean cloth.
After the wall is completely dry, knead the cement or putty to repair the wall. Let the material dry and then apply a moisture sealant. Let it rest for 24 hours between coats.
Finally, it’s time to repaint the wall to restore it to its original appearance.
The trick described above is not always decisive. Sometimes it may be necessary to apply it every two or three years, because saltpeter tends to reproduce.
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