Question:
When one is in the middle of washing for bread (having washed one hand already), can he say Amen?
What about after having washed both hands, and before the bracha of al netilas yadayim?
What about between the bracha and the drying?
Answer:
You can answer Amen in all the above cases. Only after blessing Hamoitzei etc before eating the bread should Amen not be said.
Sources:
O:CH 166 Mishnah Berurah 2, 167 Mishnah Berurah 35, ibid Shaarey Teshuvah 3, Kitzur Shulchan Aruch 41:2
