Sorry for late reply. Real life or RL as the cool kids call it has had me quite busy this last week. Thanks for your comment.
I normal use sand which has sharp grains from rivers or glaciers. Beach sand has more round grains due to millions of years of erosion. The sand in these sculptures also has some natural clay or silt which acts like a cement holding the grains together. The sand is delivered to me loose and then I compact it into wooden boxes creating a solid mass.
I then carve the sculpture from this block. Sometimes if I want to preserve the sculpture for a long time I will spray the surface with a very dilute PVA glue and this will protect it from the wind.
In general the sculptures iare just sand and water and the spray coating is only like a fixative but doesn't add much strength. I hope this answers your question.
!ENGAGE20