Is it correct to use "grounds-up" (intended meaning: "done from scratch", contracted from the expression "From the ground up"), as an adjective?
E.g.,
"This is a grounds-up implementation of the back-end server."
The correct term is "from the ground up" which calls to mind how a building is built.
See from the ground up from TFD Online.
from the ground up
starting with nothing The company was built from the ground up by two very creative people.
edit
OP refined his question in the comment, and here is my reply:
You could easily use the singular version as an adjective ("a from-the-ground-up implementation"). There would be a potential confusion, however, by merely calling something a "ground-up implementation" because that would invoke the idea of something that had been subjected to a grinding process. I'd advise using the whole phrase. But the point is never to use "grounds up".