Renovator tipped varnish to restore front of mantel (10)
I believe the answer is:
moderniser
'renovator' is the definition.
(someone modernising or renovating something)
'tipped varnish to restore front of mantel' is the wordplay.
'tipped' says the letters should be written backwards.
'varnish' becomes 'resin' (varnish is a type of resin).
'to restore' becomes 'redo'.
'front of' says to take the initial letters.
The initial letter of 'mantel' is 'm'.
'resin'+'redo'+'m'='resinredom'
'resinredom' written backwards gives 'MODERNISER'.
(Other definitions for moderniser that I've seen before include "innovator" , "One who updates" .)