Fine plaster, grey, not to be considered (5)
I believe the answer is:
grout
'fine plaster' is the definition.
'grout' can be an answer for 'plaster' (I've seen this before). I'm not sure about the 'fine' bit.
'grey not to be considered' is the wordplay.
'grey' becomes 'gr' (I've seen this in other clues).
'not' becomes 'o' (I've seen this in other clues).
'to be considered' becomes 'ut' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gr'+'o'+'ut'='GROUT'
Can you help me to learn more?
(Other definitions for grout that I've seen before include "Tile fixer" , "Grub" , "Filling for joints between tiles" , "Fill the cracks" , "cement" .)