if i were repairing the coving i'd cut out the damaged area with a stanley knife and fill the hole with decorators caulk to just below the surface of the coving and fill the rest with filler as thin as you can,let it dry rub it down with fine sandpaper, put another thin coat of filler on and rub down again.the trick is not to do too much sanding when you've filled with filler otherwise you start rubbing the paper off the coving.most people make the mistake of putting filler on too thick.if some of the coving is loose you can put a nail through the coving to fasten it back to the wall,BEING CAREFULL NOT TO NAIL THROUGH ANY ELECTRIC CABLES UNDER THE PLASTER.If theres a light switch or a plug socket below where you want to nail, chances are there is a cable running up the wall into the cieling, just something to be aware of.safty first.
phil holmes
August 2009