The control joints can be placed underneath the concrete during placement or tooled in. Depending on the job,cutting after the material is placed with a saw-cut control joint in concrete can be made. Because even new concrete cracks help induce cracking in a controlled manner. Without the addition of control joints,cracks would randomly appear. The expansion board is used to provided relief and the ability for concrete to move without binding. Heave and freeze-thaw are the culprits. Depending on when you concrete is poured,and the time of the season, curing fluctuates wildly. It is best to speak with a representative that can help you understand how long you will need to stay off the new concrete so that it will not harm your concrete or warranty. If in doubt, 28 days is standard under average temperatures in Canada.