After a newly cleaned drive or patio it may be that sanding is required.
All professional cleaning companies will offer this service
When sanding it is best to use good quality kiln dried sand, this is so the sand very easily will go in between the gaps.
Sanding helps in two main areas:
1 sanding helps to maintain the evenness of the area.
2 Sanding helps moss and plants coming through the gaps after the clean.