Nightmare!
The detailing is hard as the blocks are usually grouted and your scrim just pulls on the stuff. Because the blocks are usually of an irregular shape, you would only get away with using soft rubber. I use a 6" squeegee, and then wrap with the scrim for detailing.
Time consuming, painful and knackers your tools.
See if it were possible to use your waterfed, give them 2 different prices.