Answer: We have already explained that one who eats a bread meal is obligated to wash his hands with a small amount of water before reciting Birkat Hamazon. We have also explained that women are likewise obligated to wash their hands with Mayim Acharonim based on the ruling of Maran Ha’Shulchan Aruch (Chapter 181) that “Mayim Acharonim is an obligation.”
Regarding interruption with speech after washing with Mayim Acharonim, the Gemara (Berachot 42a) states, “Immediately after hand-washing, one must recite the blessing.” We have already explained in a previous Halacha that the Rishonim disagree regarding whether the Gemara is referring to Netilat Yadayim before the meal or the hand-washing (Mayim Acharonim) following the meal. Indeed, the Rambam explains that the Gemara is referring to the prohibition to interrupt between Mayim Acharonim and Birkat Hamazon. However, it is permissible to interrupt with speech or unrelated matters between Netilat Yadayim and the “Hamotzi” blessing according to the Rambam’s opinion.
Others explain that the Gemara is referring to the original hand-washing, i.e. Netilat Yadayim, and thus, one may not interrupt with speech or other matters between Netilat Yadayim and the “Hamotzi” blessing. Maran Ha’Shulchan Aruch rules in accordance with the Rambam’s opinion in that according to the letter of the law, one may interrupt between Netilat Yadayim and the “Hamotzi” blessing (although it is preferable to take care not to speak then either, as we have explained); however, it is forbidden to interrupt between Mayim Acharonim and Birkat Hamazon.
Maran writes in his commentary on the Rambam, Kesef Mishneh, that according to the opinion of Rashi and the Rambam, the only kind of interruption forbidden between Mayim Acharonim and Birkat Hamazon is an actual interruption, such as eating or drinking; however, there is no prohibition to speak between them. Nevertheless, in his Bet Yosef (commentary on the Tur), Maran changes his mind and writes that it seems according to all opinions that the reason to prohibit interruption between Mayim Acharonim and Birkat Hamazon is because immediately upon washing with Mayim Acharonim, one is considered to have begun blessing since Mayim Acharonim is a preparation for Birkat Hamazon. Thus, even speaking is forbidden between Mayim Acharonim and Birkat Hamazon.
Halachically speaking, one must act stringently and refrain from speaking at all between Mayim Acharonim and Birkat Hamazon. If one has already spoken between Mayim Acharonim and Birkat Hamazon, one should preferably wash one’s fingers once again as Mayim Acharonim in order to place Mayim Acharonim and Birkat Hamazon immediately one after the other without any interruption between them.