A check on waterproof road surface (7)
I believe the answer is:
macadam
'road surface' is the definition.
(I've seen this before)
'a check on waterproof' is the wordplay.
'check' becomes 'dam' (dam can mean to check or restrict water).
'on' means one lot of letters go next to another.
'waterproof' becomes 'mac' (mac is a kind of waterproof).
'a'+'dam'='adam'
'adam' after 'mac' is 'MACADAM'.
(Other definitions for macadam that I've seen before include "Road surfacing material" , "(Inventor of) road surface" , "Road-surfacing material" , "Material for roads" , "stones on the way" .)