Having the mixture too wet is careless (6)
I believe the answer is:
sloppy
'careless' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for sloppy that I've seen before include "maudlin" , "Slipshod" , "Imprecise; wet" , "Careless; watery" , "Mawkish" .)