Just go for it! I use straight portland cement watered down just enough to get it soaked into the cloth. For poured cement projects I use 1/3 to 1/2 cement and mix in sand and/or gravel, or perlite, or vermiculite.. I have had a few tufa projects crack so using a higher portland amount is safer in our warm southwest environment. I've never had any of my material projects crack, and frankly I find them easier to work with.
