How to repair cracks in plaster
Before you start, make sure the surfaces of the external corners are clean. Measure the height of the external wall and if there are any windows, their height and length as well. These are the measurements you'll use to cut your angle bead.
When applying the adhesive you want it 2mm thick and 25mm wide, either side of the corner. Applying the adhesive is the same as applying render, just flip the hawk onto the trowel to pick up the adhesive and using your ladder, apply it from the top of the wall to the bottom.
To fix the angle bead to the corner, push it into the bed of adhesive. Use a slight up and down motion to help it sink into the adhesive. Push your straight edge, hard up against the angle bead, to make sure there aren't any hollows or bumps in the bead.
Leave it to dry for five minutes. Then use your trowel to remove the excess adhesive down the bead. Flatten off the excess by angling the trowel slightly and pushing the adhesive away from the bead. Do this on both sides of the bead from top to bottom.
Apply a 2mm thick and 25mm wide layer of adhesive around the corners of the window ledge. Follow the same process as you did on the corners. Make sure that the beads are at right angles in all of the corners of your window. Then let the adhesive dry for five minutes and use your trowel to smooth off the excess adhesive as before. Leave for 24 hours to dry completely.