I built a house from the ground up and left an unpainted (only primed white) amah by amah square. The rest of the wall is painted grey, so the square is clearly visible and looks un-finished. However, I was wondering if this is OK for zechur L’churban, or do we need to shave down the wall to expose the plaster after the fact?
According to halacha, the primed white ‘ama al ama’ is enough, as the other walls are painted gray and therefore it is clear that the ‘ama al ama’ is unfinished. However, the minhag (custom) is to scrape away all of the paint and expose the plaster.
All the best
See Mishna Berura 560:3, and Igros Moshe O:CH 3 siman 86 where Rav Moshe explains that an ‘ama al ama’ of plaster mixed with sand suffices (“אף שהוא חסרון מעט”). In addition, see Kaf Hachaim O:CH 560:8 who writes that a person can make a black ‘ama al ama’ that is not painted nicely but rather looks dirty .