Moss is a common issue in lawns.  It will appear if you have shade issues of varying degrees.   Poor air circulation, poor drainage, compacted soils and soils with low fertility or a low or high PH balance are other factors which can cause moss.

Weak lawns and poor lawn care practices encourage moss.  Irregular mowing and mowing your grass too short are also common reasons why moss will come in your lawn. 

Applying little or no fertiliser is a further common problem leading to poor turf growth allowing moss to establish overtime.

Prevention is better than cure.  A good lawn management routine including scarification and aeration will help.  Consider your mowing regime and use a regular quality fertiliser programme to encourage vigorous grass growth and keep moss at bay.

If  you re-turf you will have a moss free lawn, however the moss spores are still in the ground and will gradually come back.   Applying a regular moss treatment will help to prevent moss from returning in the future.