When should you drill to 20% instead of 40% of the concrete slab?
The ASTM standard says to drill down 20% into the slab, IF the slab is drying from both sides. That means there’s going to be air movement consistently on both sides of that slab. The reason for that is because that drying curve starts drying at the top surface but hits its wettest point in the middle. Then it starts to dry out again at the bottom because you have air movement and evaporation from both sides.