think that is a good plan. That is what I did and I am happy with the medium I ended up with.
Here is a photo I took of my Turface after sifting (top left) and the granite I found before sifting (bottom). The smaller pieces of Turface on the right are the smaller
discarded pieces that fell through the sieve. ...My sieve might have been just a little too big, and filtered out a little too much, but I am still happy with the results.