Some thoughts on lapping waterstones
Olivia turned me on to the Dieter Schmid's Fine Tools site some time ago and it is where I bought my Naniwa superstones. I paid more but the 20mm thick no base feature appealed to me. This site has a section on using Japanese waterstones here and they recommend soaking the stones for 6 to 10 minutes before lapping. JimR, who lives in Japan, was kind enough to call Naniwa at my request to find out if they recommended soaking the stones and they said it was optional IIRC.
What I started doing is spraying the hone liberally with water and walking away for five minutes. I come back and draw a pencil grid and lap under running water. I have found that letting the water sit on there for five minutes seems to cut my lapping time down considerably. I'm assuming it is softening the binder but I'm not sure.
I lap my synthetics before every honing session regardless of which brand of stone. I always use a pencil grid and so far so good. I find the grid is the best way to really know what is going on with my lapping. For one thing it proves to me that even if I only hone one razor and come back to the hones a week later they do change and need to be lapped if they are going to be absolutely flat.
I am going to take one of them and check it with a micrometer and make a note of the thickness before I lap and after. I will do this for awhile and see how much I am losing. My impression is that it is not very much per session.