Excuse if this has been asked often before.

What is lawn sand and how is it different from the five or more varieties of
sand available in my local Homebase (Silver sand, Coarse building sand, fine
sand, play pit sand.....).

I'm just slightly worried that some sands contain additives or gravel that I
do not want. The Homebase guys were pleasant and helpful but not very sure
of their facts.

I just want to spike the lawn and brush in some sand to help the drainage.