Recently had all our internal doors changed,so now need to fill the holes left by the old striker plates. Carpenter suggested Ronseal white wood filler,but neglected to mention that it was a 2 part thing where you have to mix hardener with the filler and then you have 20 mins to use it I mixed the smallest amount they suggested,which should have done 2 door frames,but by time I'd done one it had gone off !! What would you use ??.