While I'm no authority on 'Tufa, (I only work in concrete & cement)...my personal guideline when mixing concrete is one designed to fit my small mixer. One fairly small handfull for roughly every 50#'s of 1:2 (cement:sand) concrete mix. It actually works out to 17#'s of cement to 34#'s of sand, so I guess you could state it that way...one hand for each 17#'s of cement. Good news is, it doesn't take much to get the benefit (which, by the way is to aid in preventing early onset or shrinkage cracks...not for added stregth later)...and it's really not that critical. Just play with something in that range and then see if what you put in gets in the way of sculpting, because that's about the only downside. The fuzzy fibers can pull out large chunks of damp medium when you are working the surface.

Best of Luck

Well, I have used the fibermesh on several pots, and am having a problem. The pots I made without fibermesh are setting up nicely and have gotten real hard. the ones I made using fibermesh at the same time as the others, are all crumbly and not getting hard. I have them wrapped in plastic to cure. Was I supposed to let them air dry instead of wrapping them in plastic? Thanks for your help