This medium lapping powder can be used to lap the backs of tools or coarse grit waterstones.
Although less extreme than the coarse grit, we recommend it only be used in extreme cases of abuse of neglect. It is not recommended in the setup of new tools, for which the fine powder is a much better choice.
The heavy scratch pattern left by this silicone carbide powder can be hard to manage. We would recommend it be worked as long as possible to refine the scratch pattern, and then followed by the fine grade powder. We use this with our mild steel lapping plate, though it greatly reduces the lifespan of the plate. Only apply this powder to one side of the plate (if you are using the coarse and medium grits, use them on the same side) and dedicate the remaining side to fine lapping.
Shapton recommends that this powder be used with it's own lapping plate to flatten medium grit waterstones, though we haven't used it in this way yet.