I'm going to split hair, in the true spirit of STW pedantry, because I'm bored. A floor made of dung is not a "turd", it is a floor.
"A turd" is a dollop of faecal matter, broadly speaking having the form it is given by the process of being expelled from the rectum. It is questionable whether it is properly applied to something too liquid to retain its shape. Using the term to describe, say, a slurry pit would be inaccurate. A slurry pit may contain matter which used to be turds, but it is not itself a turd, and it probably does not contain turds either as they will havee been broken down into an amorphous mass, losing their shape and individual identity. Using the epxression to describe a floor made of dried faecal matter is likewise inaccurate.
It remains true that you cannot polish a turd. I accept that you can polish a floor, even if it is made of dried faecal matter. Clearly, the expression "you cannot polish a floor" isn't a thing. If it was, I agree that it would be manifestly incorrect. 🙂