1
general::
Phrase(s): slow but sure [and] slowly but surely
slow but unstoppable. • Bob’s progress on his novel was slow but sure. • Nancy is finishing the paint job on her house, slowly but surely.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Gradual or plodding but certain to finish, as in Slow but sure this book's getting written. This idiom was first recorded in 1562, although the idea is much older. A related phrase appears in the proverb slow and steady wins the race, which is the moral of Aesop's fable about the race between a tortoise and a hare, which stopped to nap during the race and therefore lost.
American Heritage Idioms