In one of the Betsy~Tacy books (Betsy in Spite of Herself), she mentions two such visits.
In one case, it is pre-telephone, and the minister's wife happens to come to call on the afternoon her mother had chosen to do some heavy housecleaning. Mrs. Ray sent her daughter to open the door while she washed her hands, took off her dusty apron, and took the towel off her hair, and greeted the minister's wife with perfect courtesy, then set everything at ease by talking about housework. The minister's wife was equally gracious, and the two ladies ended up having a nice, comfortable afternoon together.
Years later, Betsy is surprised dyeing Easter eggs (a rather sweaty, messy business before microwaves and instant dyes) with her little sister by her kind of snobby beau and his much snobbier sister. She excuses herself to wash her hands and take her towel/apron off, then tries to continue being gracious by having her little sister show off the eggs and make light of what messy work it can be. However, the snobby beau and sister are not particularly gracious about it, and make it clear she has made a bad impression by not being in perfect order when they showed up, unannounced (and both parties did have telephones, so no excuse there either).
Being taken unawares isn't rude in and of itself, especially in pre-telephone days. Making the most of it is the most gracious thing to do, and a properly mannered guest will work with you.