Charlie...
I don't think there is a limit to how thick ice can get. The two variables here would be pressure and temperature. In other words as long as the ice on the surface is not melting, there would be a certain amount of pressure and the ice at the bottom would come in contact with water, and that water would begin to freeze. This would continue to happen causing the ice to get thicker and thicker. Only when the temperature got above 32 and the ice at the surface began to melt, causing less pressure on the ice below, would the thickness of the ice cease. In other words, if the temp stayed at 40 degress below zero for an entire year,the thickness of ice in a deep lake would increase a certain amount every day. Boy, I sure hope this isn't confusing and again theses are only my thoughts!