The ratio I found was 2.5 parts CWF and 1 part water. Thins it down so you do not have to sand as much, and it smooths out nicely, and is dry enough to not warp balsa...Carpenters' Wood Filler. From Elmers. Lots of people swear by it, and for good reason. Thin it just a little bit with water. How much? People "to the consistency of peanut butter" but I think they must have different peanut butter than I do, 'cause I think it matches that description right out of the tube. So, well, a little. Just a little.
YMMV