JJ ,
How long before the sand sets up with the Portland Cement added to it. I would imagine that it only sets up enough to keep the sand together and not spreading or running off instead of a strength type bond. Am I thinking along the right lines. I was thinking of either building a 2x4 wall or using metal angle between the channels and pouring about a six inch rail of concrete to go between the rails and fill the middle with sand to level it off even with the upright channel supports and then I would have a firm level base to lay my 2" foam board on. I am thinking this way the sand wouldn't run out. Please advised. Thanks.
Aranon