This is possible and will depend in particular on whether the curvature is natural or not and on the intensity of the curvature. A minor deviation in flatness formed naturally will have no effect, whereas a slightly more pronounced curvature or one resulting a priori from handling, will be likely to cause its surface sub-grade to fall. On the other hand, excessive curvature or torsion will lead to a refusal of grading in order to avoid an unsightly final result in our case.