If it's raining: Brush away any ponded water from the area of repair.
If it's dry: Get rid of any dust or dirt with a stiff bristle brush.Damp down the surface with white spirit.
Use a trowel or pallet knife to work the mastic into the repair.
For small cracks & holes: Pack the repair with a thick layer of the mastic. Make sure you cover the whole area plus about 10cm around it.
For larger cracks & voids: Use a scrim bandage to reinforce the repair. Put a thick layer of the mastic over the repair and then embed the bandage into the coating. Complete the repair by covering the whole area, plus about 25cm around it.
Clean your equipment with white spirit.