Glueing sand?

I did a project similar to this. I came up with an easy, cheap hack: use sandpaper! Here it is: https://www.frugalfamilytimes.com/2012/09/inspired-by-beach-glassartwork-for-our.html?m=1

Thats a tricky one. My attempt would be to use an clear epoxy pour let it set up some and apply sand to the top layer hoping the set up will allow it to stick on top vs sink. Bondo or even caulk might be other options to think about.....

Elmers glue dries clear and is cheap. I have heard of people using hair spray but don't have any personal experience with that myself. You could try a hot glue gun but be careful not to burn yourself.

Monica: maybe you could put SANDPAPER in first!

I agree with nan stick a sheet of sandpaper in. It's so well bonded it will be easy to stick items over it

Brush glue on with a foam brush. You can also slightly water down the glue if that helps it brush better. Apply sand. Dump off onto plate. Apply sand again. Dump again. Let dry. Spray with clear coat sealant!

Are you looking for something fairly flat, with a particular all-over depth, or something shaped?

Flat

Mix equal parts white glue with sand & apply a thin layer. When slightly tacky, sprinkle on a bit more dry sand. Let dry. Shake off any loose sand & hit with a clear sealant of your choice.

All-over Depth

Mix white glue with equal parts pencil shavings and/or sawdust. Apply a thin layer, let dry, & repeat as needed. (Wood shavings are lighter than sand but will give more texture for the next layer to cling to.)

When the depth is almost right, make the last layer sand & glue, as above.

Shaped

Get your rough shape with moldable wire mesh, carved floral foam, doodles of hot glue, or even wood cuts. Tear used course sand paper into strips; you want it soft enough to work with, but to still have some grit. Glue the paper backing to your form with an appropriate adhesive.

As with the flat effect, mix your white glue & sand. Apply a thin layer over the grit side of your sandpaper. Et cetera.

Good luck with your project