I have a 50x23 rink in Massachusetts. The ground is pretty sloped so the water is about 4" at the shallow end and more like 18" at the deep end. The rink freezes fine, but I had a question about the ice at the deep end.
I've noticed that at the deep end the ice looks more 'wet' (its not actually wet - just the ice is a different color), presumably because there is water underneath. Whenever we have snow, the deep edges get the most slushy. I was thinking this was because the water was wicking out, or the weight of the snow was pushing up the water around the edges. The ice also seems to melt first at the deep end.
I was wondering whether the boards being exposed to the air at the deep end is not allowing the water to completely freeze - would insulating the boards help? e.g. putting a layer of that pink house insulation against the outside of the boards?