A small paint run is being repaired. Technician A says to block sand the run with #600-grit wet sandpaper to quickly plane the area level. Technician B says to start by sanding with much finer sandpaper, such as #1500 grit. Who is correct?

The reasoning behind Technician A's approach is rooted in the need to efficiently level the surface of the paint run. Using #600-grit wet sandpaper is an appropriate choice for this task because it strikes a balance between effectively removing material and not being too aggressive. Starting with a coarser grit like #600 allows for quicker material removal, facilitating the smoothing process over the run to achieve an even surface. This is particularly important when addressing a defect that needs to be corrected, as the goal is to blend the repair area with the surrounding paint as seamlessly as possible.

In contrast, Technician B's suggestion of starting with a much finer grit like #1500 would not be suitable for this initial stage. Fine grits are typically used for final finishing once the majority of the defect has been addressed. Beginning with an overly fine grit would result in slower progress and may not adequately level the paint run, making it more challenging to achieve a smooth repair.

Thus, Technician A's method is correct as it aligns with the logic of addressing the immediate need to level the surface efficiently before progressing to finer sandpapers for finishing work.