Lay down asphalt (4)
I believe the answer is:
pave
'lay down asphalt' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pave that I've seen before include "Cover with flagstones" , "Cover with slabs" , "Put on a surface of stone slabs" , "Surface with stone etc." , "Cover with flat stones" .)