Ballast from tile grout and sand - Model Railroader Magazine

Jeff:

Grout(ing) sand is typically used for interlocking paving stones as opposed to ceramic tiles. It is more commonly referred to as Paver Sand or Paving Sand.

As someone mentioned there is a lot of variation in the size of the individual granules. In fact, that is how it locks the pavers together.

Some of the grouting sand is 'polymerized' in that it has a plastic compound mixed in that will set up once the sand has been wet down. Note that it does not set hard at all, and the polymer would certainly not provide enough adhesion to hold it in place if used as ballast. In my experience the polymer would stay just stickey enough and loose enough to cause all sorts of problems with track switches and, heaven forbid, locomotive gears and motors. I would strongly recommend stearing clear of the polymerized stuff.

Others may have had different experiences, and remember we are talking paving stone sand, not the stuff used for ceramics and marble.

Dave