不必疊床 (불필첩상)床 can mean either "floor" (마루) or "wooden bed" (평상), but here I think it means "floor." I could not find this expression in any dictionary, so in such cases I usually go to the Korean Web site "Annals of the Joseon Dynasty" (조선왕조실록) and search there. During my search I found a record that said "There is no need to stack roofs, and there is no need to stack floors." That was when I realized that "no need to stack floors (不必疊床)" meant "There is no need to repeat something you have already built or done."
There is no need (不必) to stack (疊) floors (床).
In the case of the diary entry in the post below this one, they had already inspected a place on Ulleungdo called "Big Hwangto Cove" (大黄土邱尾 - 대황토구미), so it would have been a waste of time and resources to do it again. That was why the expression "no need to stack floors (不必疊床)" was used.
By the way, 구미 is a pure Korean word that means "cove" or "inlet," but since pure Korean words are not based on Chinese characters, the inspector who wrote the report had to choose two Chinese characters to represent the sound of the pure Korean word for "cove." He choose the Chinese characters 邱尾 (구미) not for their meaning, but for their sound. Afterall, 邱尾 means "hill tail" (언덕 꼬리), which does not have anything to do with "a cove."
I have also seen the sound for the pure Korean word for "cove" represented by the characters 龜尾 (구미), which mean "turtle tail." The Chinese characters for the City of Gumi (구미시) in North Gyeongsang Province, for example, mean "Turtle Tail City" (龜尾市), but who in their right mind would name their city "Turtle Tail"? Therefore, I think the meaning of Gumi City (구미시) is not really "Turtle Tail City," but rather "Cove City." That means it probably started at the cove of a river, and THIS Korean Wikipedia article on the City of Gumi seems to confirm that.