I finally broke down and bought a DMT coarse for lapping. Amazing how heavy this thing is. It definitely does a better job than sandpaper sitting on my marble counters. It made quick work of my Coticule 7x2 and Shuobudani Type 100. The Naniwa 3/8 was a lot more work and I started to work on my C12k but it is so big and hard I am worried about wearing out the DMT. It also had a lot of surface tension on the Naniwa and PHIG and it became hard to move them on it. Any tips for overcoming the surface tension for large stones like the Naniwa or PHIG.

How long do DMT's last when used exclusively for lapping.