Scrim can be used on internal corners to prevent the plaster from cracking but external corners require special attention due to the fact that they often receive the occasional knock or bump. In older properties it is not unusual to find wooden beading running down the corners of external corners on chimney breasts etc. Today either galvanised metal corner beading or plastic corner beading is used. This should also be used to bead reveals around windows etc. as these are areas which are prone to the occasional knock!
Here is one of the external corners of the reveal around the window. This will need beading with either galvanised steel or plastic beading to protect it from impact damage.
Fasten the beading into place using dry wall screws.
Once all beading and taping has been carried out the boards can be skimmed using skimming plaster. Plaster skimming
External angle beading