trouble with gluing sawdust

Hello everyone, I'm having trouble glueing sawdust that I colored with fabric dye. The sawdust is well dried out. I'm glueing it on a peice of 4x8 foam board. I pealed off the silver sheeting to exposed just the foam. I mix a 50/50 mix with basic elmers white glue and put two drops of dish liquied. Is there a right way of doing this. My track is laid out and properly covered. And have a nice dark brown colored for my base. The saw dust is finely ground down as well.