 Agent Orange: Friendly fire that keeps on burning. | Inside a shed with no sunlight drying is good. As long as concrete doesn't dry, it is continuing to gain strength and will for at least 100years. Here is a graph that shows strength for time curing:
 As you can see, the slab will have about half it's strength after five or six days. 28 days is for all practical purposes going to be nearly at its max. That is if its not allowed to dry. If you let it dry, all bets are off. |