How old should concrete be at the time of sandblasting?
The time when sandblasting is done must be determined by considerations of scheduling, the hardness of the aggregate, the visual appearance desired and factors that affect the economics. Soft aggregates tend to abrade more if blasted after the concrete strength is high. If it is desired that the aggregate be highly revealed, sandblasting should be done during the first one to three days but not before the concrete has achieved the strength of 2000 psi. The age when the concrete is sandblasted should be determined for each job and then the same age should be used throughout the work in order to assure uniformity.