Yesterday, I glued sand onto the two small boards I'm making for MoM: I covered the boards in unthinned white glue, and piled a think layer of sand on top. The whole shenanigan is situated in our 'conservatory' which becomes very hot when the sun is shining like it is presently.
Today, I removed the loose sand, and then covered the boards with thinned down white glue (milk-like cosistency), with a little wash-up liquid added.
The thinned glue seals the sand, and makes the surface very hard an durable.
Here are the boards, covered in wet glue: