Hardened up like some white stuff (3)
I believe the answer is:
set
This might be a double definition.
'hardened up like some white' is the first definition.
'set' can be an answer for 'hardened' (I've seen this before). I'm unsure of the 'up like some white' bit.
'stuff' is the second definition.
(I know that stuff is a more specific form of cram)
Can you help me to learn more?
(Other definitions for set that I've seen before include "'Put, place or fix in position (3)'" , "number of games" , "What the Sun regularly does" , "Ancient god" , "Congeal" .)